Reed Switch Glossary

Alternating Current or AC is a type of flow of electric charge which periodically reverses direction. Reed Switches with special contact materials can switch up to 200W of Line Voltage loads.

The time interval from coil energization, to the closing of the reed contact. Where not otherwise stated, the functioning time of the reed contact in question is taken as its initial functioning time, not including contact bounce.

Buzzing or Aging is a process by which a batch of reed switches are operated mechanically with no load, inside a coil. Buzzing stabilizes the contact surface of a reed switch but does not degrade it as there is no connected load.

AlNiCo is a type of permanent magnet which is made from an alloy of Aluminium, Nickel, Cobalt and Iron. AlNiCo magnets are suitable for Reed Switch applications that require a high service temperature as some grades of AlNiCo magnets can work up to 550C.

Alternating Current or AC is a type of flow of electric charge which periodically reverses direction. Reed Switches with special contact materials can switch up to 200W of Line Voltage loads.

Ampere-turn or AT is the SI unit of magneto-motive force and is a direct measure of a reed contact's magnetic sensitivity. The equivalent CGS system unit is Gilbert, and 1 Ampere-turn = 4π/10 or 1.256 Gilberts. AT is also denoted as NI which denotes the product of the number of turns in the test coil N and the current I.

Ampere-turn/metre is the SI unit of coercivity. The equivalent CGS system unit is Oersted, and 1 Ampere-turn/metre = 4π/1000 or 0.0125663 Oersteds.

Annealing is a process of heating a material quickly and cooling it down slowly, in order to reduce internal stress. Annealing of Reed Blades is conducted in a controlled atmosphere to prevent oxidation and to restore the mechanical and magnetic characteristics altered during Pressing.

An Anti-ferro-magnetic material is a substance that exhibits anti-ferro-magnetism.

Anti-ferro-magnetism is a phenomenon by which a magnetic field creates parallel but opposing spins and varies with temperature.

Contact Protection or Arc Suppression is required when a reed contact is being used to switch an Inductive Load or a Capacitive Load where surge current or in-rush current is present. Additional components like resistors or capacitors may need to be added for protection from in-rush weld, chatter or Back EMF. Not using recommended methods for contact protection will lead to early failure of the Reed Contact.

Arcing is the discharge of current that jumps a gap in a circuit or between two points. When the switching voltage and/or switching current of a reed switch is at the maximum specified limits, arcing happens and degrades the contact coating, thereby reducing life.

A Reed blade, commonly known as an armature, is one of the two flattened parts that form the cantilever and current carrying parts of a reed switch. Two of these reed blades are hermetically sealed at either ends of a glass tube to form a Reed Switch.

Back Electromotive Force or Counter Electromotive Force, is the EMF that pushes against the current that induces it. In other words, it is the voltage that occurs in electric motors where there is relative motion between the armature of the motor and the magnetic field from the motor. Such Inductive loads are damaging to Reed Switches and will require Contact Protection to allay the effects of back EMF.

Bake-out is a process by which parts are exposed to heat in a controlled atmosphere to release volatile compounds as a form of cleaning or processing. Reed Blades are baked-out after deposition of contact material to improve bonding and to burn off surface organics.

A Bi-stable is an electronic circuit that has two stable states. Latching type of reed contacts are bi-stable.

A bias is a permanent magnet placed near a reed contact to oppose or aid its operation. Normally-closed reed contacts use a biasing magnet to oppose the actuating magnet. Latching reed contacts use a biasing magnet that aids and opposes the latch and unlatch operations by the actuating magnet.

Bifilar Winding or Parallel Winding, is a coil with two windings, with the wire of each winding alongside the other, matching turn for turn. The two wires are wound simultaneously with the turns of each winding being contiguous.

Contact Bounce or Chatter or Bridging, is the undesired intermittent closure of open contacts or opening of closed contacts. It may occur either when the reed contact is operated, released or when subjected to external shock or vibration. When a reed contact is actuated and the blades touch one another under the force of actuation, they are supposed to establish continuity in a single, crisp moment. Due to the mass of the moving blade and the spring-back, a reed contact will "bounce" upon closure for a small period before coming to a full rest and providing unbroken contact. Bounce time is typically less than 1 mill-second, but can be reduced progressively by using stronger magnets.

Bounce Time of a reed contact, measured in milli-seconds, is the time taken for the contact to bounce for a period of milliseconds before coming to a full rest and providing unbroken contact. This is normally in the range of 0.5 ms to 1 ms. Increasing the over-drive reduces the bounce time.

Release or Break, is defined as the opening of closed reed contacts.

A Form C or Break Before Make type of reed contact is a change-over type of contact having three leads. On actuation, the common lead makes breaks contact with the NC lead before making contact with the NO lead. This type of reed contact exhibits dwell.

Breakdown Voltage or Dielectric Strength, measured in Volts, is the voltage which may be applied across the leads of a reed contact in open condition, without causing contact damage, arcing, or causing excessive leakage. When checking the breakdown voltage for a reed switch, the second breakdown is always lower and more stable than the first. Measuring the breakdown voltage of a reed contact is a destructive test and could erode the contact.

Contact Bounce or Chatter or Bridging, is the undesired intermittent closure of open contacts or opening of closed contacts. It may occur either when the reed contact is operated, released or when subjected to external shock or vibration. When a reed contact is actuated and the blades touch one another under the force of actuation, they are supposed to establish continuity in a single, crisp moment. Due to the mass of the moving blade and the spring-back, a reed contact will "bounce" upon closure for a small period before coming to a full rest and providing unbroken contact. Bounce time is typically less than 1 mill-second, but can be reduced progressively by using stronger magnets.

Buzzing or Aging is a process by which a batch of reed switches are operated mechanically with no load, inside a coil. Buzzing stabilizes the contact surface of a reed switch but does not degrade it as there is no connected load.

Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft bluish-white metal is chemically similar to Zinc and Mercury, and is toxic. This metal is banned by the RoHS directive.

Capacitance is the ability of a system to store an electric charge, and is expressed in Farads. Reed Switch control circuits should be designed to ensure that stray capacitance does not discharge across the reed switch during the time of closure as this will degrade the contact and reduce life.

A capacitive load is a type of load that contain little resistance or inductance and mostly capacitance, for example, single-phase motors, buried cables or power supplies. In other words, it is a type of load in which the current wave reaches its peak before the voltage. Reed Switches need to be protected when used with capacitive Loads.

Carry Current, Ampere Capacity or Ampacity of a reed contact, measured in Amperes, is the maximum current that can be applied to an already closed contact. The rated carry current of a reed contact is usually slightly higher than the operating current.

The Centimetre-Gram-Second or CGS system of units is a variant of the metric system of physical units based on the Centimeter, Gram and Second as fundamental units.

Contact Bounce or Chatter or Bridging, is the undesired intermittent closure of open contacts or opening of closed contacts. It may occur either when the reed contact is operated, released or when subjected to external shock or vibration. When a reed contact is actuated and the blades touch one another under the force of actuation, they are supposed to establish continuity in a single, crisp moment. Due to the mass of the moving blade and the spring-back, a reed contact will "bounce" upon closure for a small period before coming to a full rest and providing unbroken contact. Bounce time is typically less than 1 mill-second, but can be reduced progressively by using stronger magnets.

Close Differential is the term used to denote a reed contact with a differential of minimum 70%. Reed Switches having a close or narrow differential operate and release within a much smaller band than Reed Switches with a standard differential of say 40%. Reed Switches with a close differential or a low hysteresis are especially useful in applications such as water meter and gas meters.

Coercivity is the demagnetization force required to reduce polarization or induction to zero.

Test Coil or just Coil, is an assembly consisting of one or more windings on a bobbin and is used in the Reed Switch industry, to measure the Operate AT and Release AT of a reed contact.

Contact Dwell is the difference, in AT, between the closing of the NO contact and the opening of the NC contact for Form C contacts, and is the difference, in AT, between the opening of the NC contact and the closing of the NO contact, for Form D contacts. In other words, an increased or decreased magnetic field is required to make the armature or common reed move from the normally open contact to the normally closed one, or vice-versa.

Contact force is the force between the two reed blades of a reed switch in closed condition, actuated with an Over-drive of at least 25%. A higher contact force ensures lower contact resistance. Factors that affect contact force of a Reed Contact are the overdrive, diameter of the blade wire, flexibility of the blades and uniformity of the annealing.

Contact gap, measured in microns, is the distance between the mating reed blades of a Reed Switch in open state. Several factors affect the contact gap of a Reed Switch. Although a Reed Switch having a lower Operate AT should have a smaller gap and a Reed Switch having a higher Operate AT should have a corresponding higher gap, this is not so. Reed Switches in longer glass tubes, consequently having more flexible blades will have a larger contact gap than a smaller reed switch with a shorter glass tube, even though they may have the same Operate AT.

Contact Noise is the irregular fluctuations that accompany a transmitted electrical signal but are not part of it and tend to obscure it. After a complete reed switch closure, the end of contact bounce will be followed by dynamic noise approaching 500 micro-volts peak to peak which decays exponentially to 50 micro-volts after approximately 3 milli-seconds.

Contact Protection or Arc Suppression is required when a reed contact is being used to switch an Inductive Load or a Capacitive Load where surge current or in-rush current is present. Additional components like resistors or capacitors may need to be added for protection from in-rush weld, chatter or Back EMF. Not using recommended methods for contact protection will lead to early failure of the Reed Contact.

Contact Rating or Maximum Switching Power, in Watts, is the maximum power a reed contact can withstand. The contact rating for a reed switch application is the product of switching voltage and switching current that will pass through the reed switch.

Contact Resistance  measured in milli-ohms, is the electrical resistance of a reed contact in closed state, as measured terminal to terminal, at their associated terminals. This is usually measured with a coil at 25% overdrive. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements.

Copper is a chemical element with symbol Cu (Cuprum in Latin) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. It is used in cladding reed switches for radio frequency switching or low thermal EMF applications.

Back Electromotive Force or Counter Electromotive Force, is the EMF that pushes against the current that induces it. In other words, it is the voltage that occurs in electric motors where there is relative motion between the armature of the motor and the magnetic field from the motor. Such Inductive loads are damaging to Reed Switches and will require Contact Protection to allay the effects of back EMF.

Contact Resistance  measured in milli-ohms, is the electrical resistance of a reed contact in closed state, as measured terminal to terminal, at their associated terminals. This is usually measured with a coil at 25% overdrive. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements.

Curie Point or Curie Temperature is the temperature above which a Ferro-magnetic material loses its Ferro-magnetism and becomes Para-magnetic. The Nicken Iron alloy used in the construction of Reed Switches tends to retain less and less magnetism as the application temperature goes up, thereby reducing contact forces and leading to a shorter operating life.

Direct Current or DC is a type of flow of electric charge which is only in one direction. In Reed Switches, the DC Contact rating is usually lower than the AC contact rating.

Dynamic Contact Resistance or Incremental Resistance, measured in milli-ohms, is the average of a set contact resistances measurements of closed contacts, when the contact is in continuous operation under load. During this time, there is no actual opening of the contact, but only a change in contact resistance. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements. DCR could be a measure of the long term durability of a reed contact.

Degreasing is a surface finishing process which involves cleansing of parts using solvents in vapor form in preparation for further operations. Reed Blades are vapour degreased to clean the contact surface prior to contact material deposition.

Variable Contact Resistance or Delta Contact Resistance, measured in milli-ohms, is the difference between the lowest and the highest Static Contact Resistance reading out of a prescribed set of test cycles. This is a measure of a reed contact's contact stability. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements.

A Dia-magnetic material is a substance that exhibits Dia-magnetism.

Dia-magnetism is a phenomenon exhibited by materials such as Copper or Bismuth, that become magnetized in a magnetic field with a polarity opposite to the magnetic force. Such materials are slightly repelled by a magnet.

Breakdown Voltage or Dielectric Strength, measured in Volts, is the voltage which may be applied across the leads of a reed contact in open condition, without causing contact damage, arcing, or causing excessive leakage. When checking the breakdown voltage for a reed switch, the second breakdown is always lower and more stable than the first. Measuring the breakdown voltage of a reed contact is a destructive test and could erode the contact.

Differential of a reed contact is the difference between operate AT and the release AT. This is also expressed in % as ((Operate Ampere-turn)-(Release Ampere-turn))/(Operate Ampere-turn) %.

A Dual Inline Package is a chip or device package that contains two rows of connection pins.

Direct Current or DC is a type of flow of electric charge which is only in one direction. In Reed Switches, the DC Contact rating is usually lower than the AC contact rating.

Release Range or Drop-out Range is the range of available or possible release AT values for a reed contact. The release range of a Reed Switch is usually lesser than its operate range.

A Dual Inline Package is a chip or device package that contains two rows of connection pins.

Dwell time, during soldering, is the amount of time a component's lead is in contact with a solder wave or the tip of a hand soldering Iron. When soldering reed switches in PCBs with plated through holes, the dwell time should not be more than 2 seconds maximum to ensure that seal integrity is not damaged.

An Electro-magnet is an assembly consisting of a coil on a soft metal core such as a Soft Ferrite, that exhibits magnetism when an electric current is passed through the coil.

Electro-motive Force is a measure of the energy that causes current to flow through a circuit. It is also the potential difference in charge between two points in a circuit.

Electro-static discharge is the release of static electricity when two objects come into contact. Unlike Hall-effect sensors, Reed contacts are not ESD sensitive and can safely be used in normal production without ESD safety equipment.

Test Coil or just Coil, is an assembly consisting of one or more windings on a bobbin and is used in the Reed Switch industry, to measure the Operate AT and Release AT of a reed contact.

Electroplating or Plating is a process of depositing a thin coating of metal on a conductive surface. Reed switch leads outside the glass are plated with pure Tin for solderability, but the preferred type of deposition for the contact area of a reed switch is sputtering as it is more uniform than electroplating.

Electro-motive Force is a measure of the energy that causes current to flow through a circuit. It is also the potential difference in charge between two points in a circuit.

Potting or encapsulation is a process of filling a housing with an electronic assembly with a compound that sets after curing, for resistance to shock and vibration, and for exclusion of moisture and corrosive agents. Reed Switch based Magnet Sensors with cables are potted with a flexible two component epoxy to ensure higher shock resistance.

Electro-static discharge is the release of static electricity when two objects come into contact. Unlike Hall-effect sensors, Reed contacts are not ESD sensitive and can safely be used in normal production without ESD safety equipment.

A Ferri-magnetic material is a substance that exhibits Ferri-magnetism.

Ferri-magnetism is a phenomenon exhibited by materials such as Ferrites, having parallel but opposite alignment of neighboring atoms. The resulting opposing moments are unequal and the material tends to exhibit a form of weak Ferro-magnetism.

A Ferrite is a type of compound that exhibits magnetic properties and is made from ceramic compounds derived from Iron Oxides such as Fe2O3 or Fe3O4 as well as oxides of other metals. There are Soft Ferrites and Hard Ferrites. Ferrite magnets are suitable for reed switch applications in highly corrosive environments.

A Ferro-magnetic material is a substance that exhibits Ferro-magnetism.

Ferro-magnetism is a phenomenon exhibited by materials such as Iron, that tend to become magnetized in the presence of an external magnetic field. The reed blades in a Reed Switch are Ferro-magnetic, but due to the special annealing process that they undergo, they tend to hold only minimum residual magnetism that does not interfere with the operation of the Reed Switch.

A Ferrofluid, is a liquid that becomes strongly magnetized in the presence of a magnetic field. It is a colloid of nano-particles of ferromagnetic material and a carrier fluid. Ferrofluids are sometimes used along with magnets in Reed switch based applications.

A Float Switch or Level Switch is an assembly consisting of a reed contact and an external magnet encapsulated in a foamed float. Float Switches change state when a particular level in a tank is reached. Reed Switch based float switches are more durable than mechanical ball-based float switches, but will need contact protection if the cables are longer than 10 meters.

A Flow Sensor or a Flow Meter, is a device used to quantify the volume of fluid passing through a point in a pipe. Reed Switch based flow sensors are built with a paddle having multiple magnets or a single multi-pole magnet that continuously triggers the reed switch to generate a square wave output that can be translated to volume of fluid.

A Flow Sensor or a Flow Meter, is a device used to quantify the volume of fluid passing through a point in a pipe. Reed Switch based flow sensors are built with a paddle having multiple magnets or a single multi-pole magnet that continuously triggers the reed switch to generate a square wave output that can be translated to volume of fluid.

A flow switch is a mechanical switch that is switched on or off in response to the presence or absence of flow of fluid through it. Reed Switches are used in flow switches to detect a set value of flow. Flow Switches can be manufactured to either operate in a normally-closed or a normally-open form.

A Form A type of contact is a normally open type of reed contact having two leads. These are omni-polar devices.

A normally open or Form A type of electrical contact is one that normally does not allows electricity to flow until it is signaled to close. Form A type Reed Switches actuate or close when a magnet is brought near its vicinity and de-actuate or open when the magnet is taken away.

A normally closed or Form B type of electrical contact is one that normally allows electricity to flow until it is signaled to open. Form B type Reed Switches actuate or open when a magnet of opposite polarity, is brought near its vicinity and de-actuate or close when the magnet is taken away. Form B type Reed Switches are manufactured with an inbuilt biasing magnet.

A Form B type of contact is a normally closed type of reed contact having two leads. Biased Form B type of reed contacts will require the opposite pole magnet to open the contact. Such devices are Polarity Sensitive.

A Form C or Break Before Make type of reed contact is a change-over type of contact having three leads. On actuation, the common lead makes breaks contact with the NC lead before making contact with the NO lead. This type of reed contact exhibits dwell.

A Form D or Make Before Break type of reed contact is a change-over type of contact having three leads. On actuation, the common lead makes contact with the NO lead before breaking contact with the NC lead. This is possible only with a small quantity of Mercury in the capsule. These are no longer manufactured as such devices are not RoHS compliant.

A Form E type of reed contact is a latching, or bi-stable type of contact having two leads. On actuation, it stays in the last energized state, without the need for maintaining the field. The state is altered by using opposite poles of a magnet or coil. Such types of reed contacts use a biasing magnet.

Kelvin Sensing or Four-terminal Sensing uses separate pairs of current-carrying and voltage-sensing electrodes to make more accurate measurements than traditional two-terminal test sockets. The advantage in using this method is that the separation of current and voltage electrodes eliminates the impedance contribution of the wiring and other resistances which is especially useful when measuring very low resistances. Testing of Reed contacts should also be conducted using Kelvin Sockets that are specially designed for Kelvin Sensing.

Gauss is the CGS unit of magnetic induction. The equivalent SI unit is Tesla, and 1 Gauss = 10^-4 Tesla. Magnet specifications usually list a Gauss value.

Gilbert is the CGS system unit of magneto-motive force. The equivalent SI unit is Ampere-turn, and 1 Gilbert = 10/4π or 0.7958 Ampere-turns. When measuring the operate AT of a reed switch using a simply power supply and a coil, it is easy to calculate the operate AT by just noting the operate current and multiplying it with the number of turns in the test coil.

Gold is a chemical element with the symbol Au (Aurum in Latin) and atomic number 79. It is a dense, soft, malleable and ductile metal with a bright yellow color and luster. Gold is sometimes used as an under-layer in reed switch contacts, but can cause some sticking. Reed Switch leads are plated with Gold to increase the shelf life.

A Hall Effect Sensor or a Hall Effect Device is a transducer which varies its output voltage in response to changes in magnetic field. Unlike reed contacts, Hall Effect Devices require amplification circuits and an external power source for operation.

A Hard Ferrite is a type of Ferrite where magnetism is inherent in the material, and does not require an external coil to stay magnetized.

A Helmholtz coil is a device for producing a region of nearly uniform magnetic field and is named after the German physicist Hermann von Helmholtz.

Hermetic describes a type of closure that is complete and airtight. Reed Switches are hermetically sealed and this prevents the switching area from effects of the atmosphere, thereby making them safe to use in explosive environments. Reed Switches are one of the few devices which continue to be used in fuel tanks for accurate measurement of volume of fuel.

Hexavalent Chromium refers to chemical compounds that contain the element Chromium in the +6 oxidation state that when inhaled, is recognized as a human carcinogen. This chemical is banned by the RoHS directive.

A homogeneous material is defined as either a raw material or a material applied during the construction of the product. For example, in reed blades sputtered with both Gold and a Ruthenium layer, the base metal (Nickel Iron alloy) and both layers are considered homogeneous materials and therefore must be considered separately.

Differential of a reed contact is the difference between operate AT and the release AT. This is also expressed in % as ((Operate Ampere-turn)-(Release Ampere-turn))/(Operate Ampere-turn) %.

Dynamic Contact Resistance or Incremental Resistance, measured in milli-ohms, is the average of a set contact resistances measurements of closed contacts, when the contact is in continuous operation under load. During this time, there is no actual opening of the contact, but only a change in contact resistance. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements. DCR could be a measure of the long term durability of a reed contact.

An inductive load is an electrical device that is made of wound or coiled wire, for example transformers, solenoid coils, motors or electro-mechanical relays that causes inrush current. In other words, it is a type of load in which the voltage wave reaches its peak before the current. Since inductive loads generate Back EMF, Contact Suppression circuits are required.

An inert gas is one which does not react with other elements. The Noble gases and Nitrogen often do not react with many substances. Reed Switches are filled with a a mixture of inert gases to exclude contaminants, prevent oxidation of the contacts, and to prevent ice formation in low temperature applications.

Inrush Current or Surge Current, measured in Amperes, refers to the maximum instantaneous input current drawn by an electrical device when first turned on. When Reed contacts are used to switch loads that have inrush current, contact protection is required.

Insulation resistance, measured in Ohms, is the DC electrical resistance measured between open terminals of a reed contact. This is generally in the 109 Ohms range for reed switches.

The Internet of Things, or IoT refers to physical objects that require an IP address, are connected to the internet, and collect and exchange information with each other via cloud services such as ifttt.com. Reed Switches and reed sensors help monitor various parameters on Internet connected devices using Apps, for example, to monitor the status of a window, or the level of water in a sump etc.

The Internet of Things, or IoT refers to physical objects that require an IP address, are connected to the internet, and collect and exchange information with each other via cloud services such as ifttt.com. Reed Switches and reed sensors help monitor various parameters on Internet connected devices using Apps, for example, to monitor the status of a window, or the level of water in a sump etc.

Irridium is a chemical element with the symbol Ir and atomic number 77. It is a very dense, hard, brittle, silvery-white transition metal and is sometimes used as a contact material in reed switches due to its resistance to arc erosion.

Kelvin Sensing or Four-terminal Sensing uses separate pairs of current-carrying and voltage-sensing electrodes to make more accurate measurements than traditional two-terminal test sockets. The advantage in using this method is that the separation of current and voltage electrodes eliminates the impedance contribution of the wiring and other resistances which is especially useful when measuring very low resistances. Testing of Reed contacts should also be conducted using Kelvin Sockets that are specially designed for Kelvin Sensing.

A Kelvin Socket or a Kelvin Clip is a special form of test socket where the jaws are insulated from each other, thereby allowing two isolated wires to connect to the device under test. It enables Kelvin Sensing which is important for measurement of very low contact resistance values of Reed contacts.

A lamp load is a type of load that generates Inrush current when lighting up, for example, tungsten filament, fluorescent or mercury-vapor lamps. Reed Switches used with lamp loads require Contact Suppression against cold filament Inrush.

A Form E type of reed contact is a latching, or bi-stable type of contact having two leads. On actuation, it stays in the last energized state, without the need for maintaining the field. The state is altered by using opposite poles of a magnet or coil. Such types of reed contacts use a biasing magnet.

Lead is a chemical element with symbol Pb (Plumbum in Latin) and atomic number 82. Lead is a soft and malleable metal, which is regarded as a heavy metal and when ingested, is poisonous. This metal is banned by the RoHS directive.

A Light Emitting Diode or LED, is a two lead semiconductor device that emits light when an electrical current is passed through it. Reed Sensors can be fitted with LEDs to indicate actuation.

A Float Switch or Level Switch is an assembly consisting of a reed contact and an external magnet encapsulated in a foamed float. Float Switches change state when a particular level in a tank is reached. Reed Switch based float switches are more durable than mechanical ball-based float switches, but will need contact protection if the cables are longer than 10 meters.

A Level Sensor is an assembly that is fitted inside a tank, consisting of a PCB with multiple reed contacts and resistors that can be actuated by a foamed float to give out a potentiometric feedback that is a direct measure of the volume of the liquid. The resistor values need to be altered for various tank shapes.

A Level Sensor is an assembly that is fitted inside a tank, consisting of a PCB with multiple reed contacts and resistors that can be actuated by a foamed float to give out a potentiometric feedback that is a direct measure of the volume of the liquid. The resistor values need to be altered for various tank shapes.

A Life Test is the process of testing a product by subjecting it to conditions in excess of its normal service parameters in an effort to uncover faults and potential modes of failure in a short amount of time. Reed Switches can be life tested for specified voltage and current levels at speeds of up to 200 Hz to predict the life cycle in the field.

A Light Emitting Diode or LED, is a two lead semiconductor device that emits light when an electrical current is passed through it. Reed Sensors can be fitted with LEDs to indicate actuation.

Line Voltage is the potential difference between line and neutral phases of a three phase Mains Electricity AC supply. Reed Switches specially coated for lines voltage applications can switch AC Mains Electricity loads directly.

Close Differential is the term used to denote a reed contact with a differential of minimum 70%. Reed Switches having a close or narrow differential operate and release within a much smaller band than Reed Switches with a standard differential of say 40%. Reed Switches with a close differential or a low hysteresis are especially useful in applications such as water meter and gas meters.

Close Differential is the term used to denote a reed contact with a differential of minimum 70%. Reed Switches having a close or narrow differential operate and release within a much smaller band than Reed Switches with a standard differential of say 40%. Reed Switches with a close differential or a low hysteresis are especially useful in applications such as water meter and gas meters.

A Magnet is a type of material, primarily of an Iron alloy, that has its component atoms so ordered that the material exhibits properties of magnetism, such as attracting other Iron-containing objects or aligning itself in an external magnetic field. Reed Switches are actuated by magnets.

Maximum Energy Product or Magnet Performance, denoted by BHmax and measured in MegaGauss-Oersteds (MGOe), is the amount of energy that a material can supply to an external magnetic circuit when operating within its demagnetization curve. In other words, it is the storage energy in a magnet and 1MGOe = 7.957KJ/m^3.

A Magnetic Proximity Sensor is a device that uses a reed switch, and is encapsulated in a housing for easy mounting or clamping and is supplied with cables. A Proximity Sensor is normally accompanied by an actuator encapsulated in an identical housing. These paired devices are tested together to ensure required operate and release distances.

Magnetic Flux or Magnetic Induction, denoted by B, is a measure of the strength of a magnetic field over a given area, and is expressed in Weber.

A Magnetic Shield or a Shunt, is a piece of metal of high magnetic permeability, that can be used to protect magnetic circuits from the effects of external magnetic fields. It can also be used to break the interaction between a reed switch and a magnet of fixed distance, by acting as a vane. Magnetic shields are also used to protect Reed Relays from stray magnetic fields.

Magnetic Field Strength or Magnetic Field Intensity, denoted by H, is the amount of magnetic flux in a unit area perpendicular to the direction of magnetic flow, and is expressed in Ampere-turns/metre.

Magnetic Flux or Magnetic Induction, denoted by B, is a measure of the strength of a magnetic field over a given area, and is expressed in Weber.

Magnetic Ordering Temperature or Neel Temperature is the temperature above which an Anti-Ferro-magnetic or Ferri-magnetic material becomes Para-magnetic. Thermal Ferrites are materials that exhibit this phenomenon.

Magnetic Permeability is the ability of a material to get magnetized in the presence of a magnetic field. The reed blades of a reed switch are made of a Nickel-Iron alloy which are magnetically permeable and this is what causes the reed blades to attract each other in the presence of a magnetic field.

Magnetic saturation exists when an increase of magnetization applied to a reed contact does not increase the magnetic flux through. In the case of a magnet actuating a Reed Switch, it is the point at which a Reed Switch attains maximum closure force and moving the magnet any closer will not matter. In the case of a Reed Switch being inside a coil, it is the overdrive beyond which the contact resistance does not drop any further.

A Magnetic Shield or a Shunt, is a piece of metal of high magnetic permeability, that can be used to protect magnetic circuits from the effects of external magnetic fields. It can also be used to break the interaction between a reed switch and a magnet of fixed distance, by acting as a vane. Magnetic shields are also used to protect Reed Relays from stray magnetic fields.

Magneto-motive force is a quantity representing the line integral of the magnetic intensity around a closed line and is expressed in Ampere-Turns.

Operate or Make, is defined as the closing of open reed contacts.

A Form D or Make Before Break type of reed contact is a change-over type of contact having three leads. On actuation, the common lead makes contact with the NO lead before breaking contact with the NC lead. This is possible only with a small quantity of Mercury in the capsule. These are no longer manufactured as such devices are not RoHS compliant.

Contact Rating or Maximum Switching Power, in Watts, is the maximum power a reed contact can withstand. The contact rating for a reed switch application is the product of switching voltage and switching current that will pass through the reed switch.

Maximum Energy Product or Magnet Performance, denoted by BHmax and measured in MegaGauss-Oersteds (MGOe), is the amount of energy that a material can supply to an external magnetic circuit when operating within its demagnetization curve. In other words, it is the storage energy in a magnet and 1MGOe = 7.957KJ/m^3.

Maxwell is the CGS system unit of magnetic flux. The equivalent SI unit is Weber, and 1 Maxwell = 10^-8 Webers.

Mercury is a chemical element with the symbol Hg (Hydrargyrum in Latin) and atomic number 80. It a is heavy, silvery metal that is liquid at room temperature and atmospheric pressure and when ingested, is poisonous. This metal is banned by the RoHS directive.

MegaGauss-Oersted is the CGS unit of the Maximum Energy product (BHmax) of a magnet.

The Metre-Kilogram-Second or MKS system of units is a physical system of units that expresses any given measurement using the three fundamental units of the Metre, Kilogramme, and/or Second. The MKS system, widely known as the Metric System, has succeeded the CGS system.

Molybdenum is a chemical element with the symbol Mo and atomic number 42. It is a silvery metal having a very high melting point. It is sometimes used as a contact material in reed switches for switching high current loads.

A normally closed or Form B type of electrical contact is one that normally allows electricity to flow until it is signaled to open. Form B type Reed Switches actuate or open when a magnet of opposite polarity, is brought near its vicinity and de-actuate or close when the magnet is taken away. Form B type Reed Switches are manufactured with an inbuilt biasing magnet.

NdFeB is a rare-earth magnet made from an alloy of Neodymium, Iron and Boron to form the Nd2Fe14B tetragonal crystalline structure. Reed switch applications that require highest magnet strength can use NdFeB magnets.

A Form B type of contact is a normally closed type of reed contact having two leads. Biased Form B type of reed contacts will require the opposite pole magnet to open the contact. Such devices are Polarity Sensitive.

A Form A type of contact is a normally open type of reed contact having two leads. These are omni-polar devices.

A normally closed or Form B type of electrical contact is one that normally allows electricity to flow until it is signaled to open. Form B type Reed Switches actuate or open when a magnet of opposite polarity, is brought near its vicinity and de-actuate or close when the magnet is taken away. Form B type Reed Switches are manufactured with an inbuilt biasing magnet.

A normally open or Form A type of electrical contact is one that normally does not allows electricity to flow until it is signaled to close. Form A type Reed Switches actuate or close when a magnet is brought near its vicinity and de-actuate or open when the magnet is taken away.

Operate AT or OAT, also known as Pull-in or PI, is the measured value in Ampere-turns, at which a reed contact closes. This is valid for the closing operation of form A, B, and E type reed contacts, and the change over operation from the normally closed contact to the normally open contact for form C and D type reed contacts.

Oersted is the CGS system unit of magnetic field strength. The equivalent SI unit is Ampere-turn/metre, and 1 Oersted = 1000/4π or 79.58 Ampere-turns/metre.

An omni-polar magnetic device fully functions with either pole of a magnet. Normally open type Reed Switches are omni-polar devices wheres biased type normally-closed Reed Switches are not and need a magnet of opposite polarity for actuation.

Operate or Make, is defined as the closing of open reed contacts.

Operate AT or OAT, also known as Pull-in or PI, is the measured value in Ampere-turns, at which a reed contact closes. This is valid for the closing operation of form A, B, and E type reed contacts, and the change over operation from the normally closed contact to the normally open contact for form C and D type reed contacts.

Operate Range or Pull-in Range is the range of available or possible operate AT values for a reed contact. The operate range of a Reed Switch is usually more than its release range.

The time interval from coil energization, to the closing of the reed contact. Where not otherwise stated, the functioning time of the reed contact in question is taken as its initial functioning time, not including contact bounce.

Operating Frequency of a reed contact, measured in Hertz, is the maximum speed at which it can be operated.

The temperature range within which a reed contact or magnet will meet all specified operating parameters.

Over-drive, stated as a percentage, is the extra Ampere-turn applied to a reed contact after closure, before measurement of Contact Resistance. This is done to fix the direction of the remanent flux. Contact Resistance of a reed contact is usually measured at 25% overdrive. Overdrive when using a magnet is achieved by moving the magnet closer than the actuation point. Using a Reed Switch in an application with a higher Over-drive gives a longer life.

Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare silvery-white metal resembling platinum and is sometimes plated below Ruthenium on reed blades to add contact thickness for close differential characteristics.

A Para-magnetic material is a substance that exhibits Para-magnetism.

Para-magnetism is a phenomenon exhibited by materials such as Aluminum or Platinum, that tend to become magnetized when a magnetic field is present, but lose it when the field is absent.

A Printed Circuit Board is a thin board made of fiberglass, composite epoxy, or other laminate material on which conductive pathways are etched or "printed", connecting the different components.

Electroplating or Plating is a process of depositing a thin coating of metal on a conductive surface. Reed switch leads outside the glass are plated with pure Tin for solderability, but the preferred type of deposition for the contact area of a reed switch is sputtering as it is more uniform than electroplating.

Polarity sensitive or Polarity dependent types of Reed contacts are those that have been biased with an internal magnet and can only be actuated by an external magnet having an opposite polarity. Form B and Form E type reed contacts are polarity sensitive.

Potting or encapsulation is a process of filling a housing with an electronic assembly with a compound that sets after curing, for resistance to shock and vibration, and for exclusion of moisture and corrosive agents. Reed Switch based Magnet Sensors with cables are potted with a flexible two component epoxy to ensure higher shock resistance.

Stamping or Pressing is a process by which metals in the shape of wires or sheets are formed using a tool or a die. Wires of Nickel-Iron alloy in different diameters are pressed using Tungsten Carbide Tools to form Reed Blades of different sizes.

A Printed Circuit Board is a thin board made of fiberglass, composite epoxy, or other laminate material on which conductive pathways are etched or "printed", connecting the different components.

A Magnetic Proximity Sensor is a device that uses a reed switch, and is encapsulated in a housing for easy mounting or clamping and is supplied with cables. A Proximity Sensor is normally accompanied by an actuator encapsulated in an identical housing. These paired devices are tested together to ensure required operate and release distances.

Operate Range or Pull-in Range is the range of available or possible operate AT values for a reed contact. The operate range of a Reed Switch is usually more than its release range.

Release AT or RAT, also known as Drop-out or DO, measured in Ampere-turns, is the point at which a reed contact opens. This is valid for the opening of form A, B, and E type reed contacts, and the change over from the closed normally open contact to the open normally closed contact for form C and D type contacts.

Re-closure of a reed contact, measured in AT, is the second closure which occurs after further energization of an already energized, normally closed reed contact in open state, or after further energization of a latching type reed contact in open state. This is applicable to biased form B and form E type reed contacts.

A Reed blade, commonly known as an armature, is one of the two flattened parts that form the cantilever and current carrying parts of a reed switch. Two of these reed blades are hermetically sealed at either ends of a glass tube to form a Reed Switch.

Contact is the current-carrying parts of a reed contact that engage or disengage to close or open electrical circuits. This area is plated or sputtered with Ruthenium, Rhodium, Tungsten or other material.

A Reed Relay is a type of Relay that uses a Reed Switch within a coil. Coils can be designed to accommodate multiple Reed Switches for designing multi-pole Reed Relays. A normally open reed switch can be biased closed with a permanent magnet or with a biasing coil to produce a normally closed reed relay, but frequently a changeover reed is used for normally closed relays.

A reed sensor is a device built using a reed switch with additional functionality or features, for example, to withstand higher shock, easier PCB mounting, additional intelligent circuitry, biased contact states, etc.

A reed switch is a passive device consisting of two Reed Blades sealed inside a glass tube with an Inert Gas, which operates when brought near a magnetic field. The reeds are hermetically sealed in cantilever form so that their free ends overlap and are separated by a small air gap. The contact area of each blade can be coated with one of many types of contact materials such as Ruthenium, Rhodium, Tungsten, Silver, Irridium, Molybdenum etc. Due to the low inertia of the Reed Blades and the small gap, fast operation is achieved. The inert gas inside the sealed Reed Switch not only prevents oxidation of the contact material but also helps in making it one of the few devices that can be used in explosive environments.

Release or Break, is defined as the opening of closed reed contacts.

Release AT or RAT, also known as Drop-out or DO, measured in Ampere-turns, is the point at which a reed contact opens. This is valid for the opening of form A, B, and E type reed contacts, and the change over from the closed normally open contact to the open normally closed contact for form C and D type contacts.

Release Range or Drop-out Range is the range of available or possible release AT values for a reed contact. The release range of a Reed Switch is usually lesser than its operate range.

Release time of a reed contact, measured in milli-seconds, is the time interval from coil de-energization to the opening or change over of the reed contact. The functioning time of the reed contact in question is taken as its initial functioning time, not including contact bounce.

Remanence is the magnetization left behind in a ferromagnetic material (such as a reed blade) after an external magnetic field is removed. Reed blades are through a special annealing process to minimize remanence.

A resistive Load is a type of load that contains no inductance or capacitance, but only pure resistance, for example, incandescent light bulbs or toasters. When a resistive load is turned on, the voltage and current reach its steady-state without exceeding it first. Unlike Inductive Loads, resistive loads do not generate Back EMF but Contract Protection for cold filament Inrush current may be required.

Resonant frequency of a reed contact, measured in Hertz, is the maximum operating frequency that a reed contact can withstand, after which it chatters, or starts sympathetic vibration.

Rhodium is a chemical element with the symbol Rh and atomic number 45. It a hard silvery-white metal of the transition series. Dues to its low contact resistance and resistance to corrosion, it is used as a contact material in the production of reed switches.

Restriction of Hazardous Substances or RoHS originated in the European Union and restricts the use of specific hazardous materials found in electrical and electronic products. It is also known as the RoHS Directive or Directive 2002/95/EC.

Ruthenium is a chemical element with the symbol Ru and atomic number 44. It is a hard silvery-white metal of the transition series. Because of its high melting point and excellent wear resistance, the use as plating or sputtering material in reed switches is preferred.

Magnetic saturation exists when an increase of magnetization applied to a reed contact does not increase the magnetic flux through. In the case of a magnet actuating a Reed Switch, it is the point at which a Reed Switch attains maximum closure force and moving the magnet any closer will not matter. In the case of a Reed Switch being inside a coil, it is the overdrive beyond which the contact resistance does not drop any further.

A shielded cable is a type of electrical cable with one or more cables inside, enclosed by a conducting layer that shields the cables from external electrical noise and interference. When reed switches are tested, shielded cables should be used to connect the device up to the test equipment to ensure accurate measurements.

Shock resistance of a reed contact, is the acceleration limit and sine-wave duration in milli-seconds that an open reed contact (with no magnetic field present) or a closed reed contact (with a 100% overdrive) can withstand without changing state. The majority of normally open reed switches should withstand a shock level of 100g at right angles to the plane of the reed blades without changing state.

The International System of Units or Système International d'Unités or SI, is the modern form of the Metric System and is the world's most widely used system of measurement. It is derived from the MKS system rather than the CGS system.

Silver is a chemical element with the symbol Ag (Argentum in Latin) and atomic number 47. It is a soft, white, transition metal having the highest electrical and thermal conductivity of any metal. It is used as a contact material in reed switches when switching Lamp Loads with Inrush, due to its resistance to welding.

A Single Inline Package is a chip or device package that contains only a single row of connection pins.

A Single Pole Double Throw switch is a type of that has a single input and can connect to a dual outputs.

A Single Pole Single Throw switch is a type of switch that has a single input and can connect to a single output.

A Single Inline Package is a chip or device package that contains only a single row of connection pins.

SmCo is a rare earth magnet made from an alloy of Samarium and Cobalt to form SmCo5 or Sm2Co17 compounds. Reed Switch applications that require stronger magnets and excellent thermal stability up to temperatures of 300C can use SmCo magnets.

A Surface-mount Device is an electronic component that mounts on the surface of a printed circuit board (as opposed to "through-hole" components there the leads are inserted into holes). These types of devices allow more components per square centimeter on a Printed-circuit Board.

Surface-mount Technology is a design standard for electronic circuits where the components are mounted directly onto the the surface of a PCB as against fixing components leads into plated through-holes and soldering below.

A Soft Ferrite is a type of Ferrite where permanent magnetism is not inherent in the material, and requires an external coil to magnetize it. It exhibits magnetism as long as the coil carries current.

Soldering is the process of joining two or more metals together by melting and flowing a filler metal having a lower melting point (normally Tin) into the joint. Soldering can be used to solder components to PCB or component leads to cables. When manual soldering reed contacts, care should be taken that the solder tip dwell is less than 2 seconds.

A Single Pole Double Throw switch is a type of that has a single input and can connect to a dual outputs.

A Single Pole Single Throw switch is a type of switch that has a single input and can connect to a single output.

Sputtering is a process that uses ions of an Inert Gas to dislodge atoms from the surface of a Target, and have them electrically deposited to form an extremely thin coating on a glass, metal, plastic, or other surface known as the substrate. Reed Blades can be sputtered using various Target materials.

Stamping or Pressing is a process by which metals in the shape of wires or sheets are formed using a tool or a die. Wires of Nickel-Iron alloy in different diameters are pressed using Tungsten Carbide Tools to form Reed Blades of different sizes.

Static contact resistance, measured in milli-ohms, is the electrical resistance of a reed contact in closed state, as measured terminal to terminal, at their associated terminals. This is usually measured with a coil at 25% overdrive. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements.

A Surface-mount Device is an electronic component that mounts on the surface of a printed circuit board (as opposed to "through-hole" components there the leads are inserted into holes). These types of devices allow more components per square centimeter on a Printed-circuit Board.

Surface-mount Technology is a design standard for electronic circuits where the components are mounted directly onto the the surface of a PCB as against fixing components leads into plated through-holes and soldering below.

Inrush Current or Surge Current, measured in Amperes, refers to the maximum instantaneous input current drawn by an electrical device when first turned on. When Reed contacts are used to switch loads that have inrush current, contact protection is required.

Switching current of a reed contact, measured in Amperes, is the maximum current a reed contact can switch. Subjecting a reed contact to a higher current can cause a weld or early failure. The switching current of a reed contact can range from as low as 1 fempto-amp up to 5A using special contact materials. When switching current of a reed contact is at its maximum specified limit, the arcing happening during operation will degrade the contact and consequently shorten the life.

Switching frequency, measured in Hertz, is the maximum frequency at which a reed contact can operate. Switching at speeds beyond this will lead to intermittent operation.

Switching voltage of a reed contact, measured in volts, is the maximum voltage a reed contact can switch. Subjecting a reed contact to a higher voltage can cause contact degradation or early failure. A higher switching voltage always results in arcing which degrades the contact and reduces the life of the reed switch. Special reed switches can switch voltages as low as 10 nano-volts up to 10 kilo-volts.

Tesla is the SI unit of magnetic flux density. The equivalent CGS system unit is Gauss, and 1 Tesla = 10^4 Gauss.

Test Coil or just Coil, is an assembly consisting of one or more windings on a bobbin and is used in the Reed Switch industry, to measure the Operate AT and Release AT of a reed contact.

Thermal EMF of a reed contact, is the electromotive force generated by a reed contact when the unit is subjected to a temperature differential. For most reed switches, this is in the region of 40 micro volts per degree Celcius.

A Thermal Ferrite is special Ferrite compound which loses its magnetic permeability and changes from being Ferri-magnetic to Para-magnetic at its Magnetic Ordering Temperature. Thermal Ferrites which operate at different temperatures can be manufactured by altering the alloy mix.

A Thermal Reed Switch is an assembly consisting of a Reed Switch, a Thermal Ferrite and two permanent magnets and this assembly works as a temperature sensor. At temperatures lower than the Thermal Ferrite's Curie Point, the magnetic flux lines between the two exterior magnets are connected and enlarged as a whole and this keeps the reed switch contact closed. When the ambient temperature crosses the Thermal Ferrite's Curie Point, the flux no longer passes between the exterior magnets, and the reed switch contact opens.

A Tilt Switch is a device used which gives out a signal at a pre-defined tilt angle. Originally, tilt switches were made of Mercury, but due to Mercury being a hazardous substance, Reed Switch based Tilt switches have been developed. A Reed Switch based Tilt Switch consists of a reed switch a moving magnet assembly in a single package, that is designed to actuate at a set angle.

Tin is a chemical element with symbol Sn (Stannum in Latin) and atomic number 50. This silvery, malleable metal is not easily oxidized in air and is used to coat other metals to prevent corrosion and can easily be soldered.

Tungsten is a chemical element with the symbol W (Wolfram in Latin) and atomic number 74. It is a hard, rare metal which is found naturally only in chemical compounds. Tungsten is used as a contact material in reed switches due to its resistance to damage by arcing, but is not be used in applications where low Contact Resistance is required.

Ultrasonic Welding is the process of joining two plastic work pieces or any other dissimilar materials by using high frequency acoustic vibrations. The work pieces are hold together under pressure. Reed Switches could be damaged by ultrasonic welding and trials are required to ensure that the harmonics of the housings and the enclosed reed switch do not interact.

Vacuum Deposition is process of deposition of a thin film or a coating made under vacuum or a low-pressure plasma environment on a substrate. This is purely a physical process rather than involving a chemical reaction. The contact area of Reed switches and related products can be vacuum deposited.

Variable Contact Resistance or Delta Contact Resistance, measured in milli-ohms, is the difference between the lowest and the highest Static Contact Resistance reading out of a prescribed set of test cycles. This is a measure of a reed contact's contact stability. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements.

Variable Contact Resistance or Delta Contact Resistance, measured in milli-ohms, is the difference between the lowest and the highest Static Contact Resistance reading out of a prescribed set of test cycles. This is a measure of a reed contact's contact stability. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements.

Vibration resistance of a reed contact, is the acceleration level and frequency range that an open reed contact (with no magnetic field present) or a closed reed contact (with a 100% overdrive) can withstand without changing state. Majority of normally open reed switches should withstand a Vibration of 20g for 11 milli-seconds without changing state, except in the region of its Resonant Frequency.

Weber is the SI unit of magnetic flux. The equivalent CGS system unit is Maxwell, and 1 Weber = 10^8 Maxwell.

Welding is the process of joining two metals or plastics by heating the surfaces to the point of melting, using a blowtorch, electric arc, or other heating sources, and uniting them by pressing. When welding reed contacts, heat sinks should be used so that the quick heating and cooling does not cause glass seal cracks.