FAQ Usage Characteristics Magnets Actuation Modifications Protection Testing Level Sensing Life Glossary

Reed Switch and Reed Sensor Definitions

Ampere Turn (AT)

The product of the number of turns of wire in an electromagnetic coil winding and the current in amperes passing through the winding. This is a direct measure of a reed contact's sensitivity.

Bounce

Intermittent opening and closing of closed contacts or closing and opening of open contacts, usually implying the motion resulting from contact impact.

Breakdown Voltage

The voltage which may be applied between insulated parts of a reed contact without damage, arcing, breakdown , or causing excessive leakage.

Carry Current (in Amps)

The maximum current that can be applied to an already closed contact.

Chatter

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.

Coercivity

Demagnetization force required to reduce polarization or induction to zero.

Coil

An assembly consisting of one or more windings on a bobbin. Used to measure AT of a reed contact.

Contact

The current-carrying parts of a reed contact that engage or disengage to close or open electrical circuits.

Contact Gap

The distance between mating reed contacts when the contacts are open.

Contact Rating (in Watts)

The maximum power, a reed contact can switch.

Contact Resistance (CR)

The electrical resistance in milli-ohms of closed contacts.

Curie Temperature

Temperature at which a magnet is totally demagnetized.

Differential

The difference between operate AT and release AT. This is also expressed in % as (OAT-RAT)/OAT %.

Dwell (for Form C and D type contacts)

For form C contacts, it is the difference, in AT, between the closing of the NO contact and the opening of the NC contact, and for form D contacts, is the difference, in AT, between the opening of the NC contact and the closing of the NO contact.

Dynamic Contact Resistance (DCR)

The electrical resistance of closed contacts, when the contact is in continuous operation under load.

Form A

A normally open type of reed contact.

Form B

A normally closed type of reed contact.

Form C

A change-over type of reed contact where break happens before make.

Form D

A change-over type of reed contact where make happens before break.

Form E

A latching, or bi-stable type of contact, which stays in the last energized state, without the need for maintaining the field.

Homogenous Materials

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 plated 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.

Hysteresis

See differential.

Insulation Resistance

The electrical resistance measured between insulated terminals.

Omni-polar

This type of device fully functions with either pole of a magnet.

Operate AT (OAT)

The measured value, in AT, 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.

Operating Temperature

The temperature range over which the reed contact will meet all specified operating parameters.

Operate Time

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.

Over-drive (in AT)

The percentage of AT given above OAT, before measurement of CR.

Pull In (PI)

See Operate AT.

Re-closure (RC)

The closure which occurs after further energization of an already energized, normally closed reed contact in open condition. This is applicable to form B type reed contacts and to the un-latching operation of form E types.

Reed Switch

A reed switch is a passive device consisting of two reed contacts sealed inside a glass tube which operates when brought near a magnetic field.

Reed Sensor

A reed sensor is a device built using a reed switch with additional functionality like ability to withstand higher shock, easier mounting, additional intelligent circuitry, etc.

Release AT (RAT)

The measured value, in AT, 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.

Reed Relays and Electronics India Limited, 2008

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