Reed Relays and
Electronics India Limited
Manufacturer of Reed Switches, Reed Sensors and Reed-based products
Reed Relays and Electronics India Limited Incorporated in 1971

Pulse Counting Type

Speedometer pulse counting
Pulse counting type application

When an application requires the volume of a fluid, or a distance, or the RPM of a machine tool measured, such an application can be classified as a pulse counting application.

The basic principle of pulse counting is to use a reed switch or a reed sensor on a fixed surface, with a multi-pole ring magnet attached or embedded to the center of the wheel or counter. The best practice is to use ring magnets with two poles for high speed applications and to use ring magnets with 4 or more poles for low speed applications, for better accuracy. When the sensing circuit is low in the range of milli-amperes, the basic reed switch does the job for up to a billion operations.

Reed Switches works so well in such applications as they have a very high operating frequency. The Reed Switches used generate a square wave that can then be translated to the actual consumption of fluid, or energy, or the measurement of wheel speeds. As the wheel rotates, the multi-pole magnet’s alternating North and South poles turn the reed switch on and off continuously and this generates the square wave pulse. This pulse output is used by control circuits to display the actual measurement. The translation of number of pulses to the actual unit of measurement is achieved initially, by conducting various trials. More information regarding magnet actuation of reed switches is available here.

For larger wheels, where the diameter of the magnet is more and the pole moves away far enough to open the reed switch, any standard reed switch with a differential of 40-50% can be used. But for very tiny wheels in water and gas meters, it is important the reed switches with a close differential or 70% minimum differential are used. This is to ensure that the reed switch opens immediately as the magnetic pole moves away, so that the reed switch does not remain closed at any point.

Reed Switches are hermetically sealed, they are immune to dust and moisture, and can safely be used in environments with extreme dirt and moisture. Pulse counting for applications can also be achieved by using active devices like Hall effect sensors, but Reed Switches and Reed Sensors, are passive, have more advantage as no power is consumed for operation, and have no leakage current across the contacts, that need to be compensated for. Some of the pulse counting applications are listed below.

Example Applications

Reed sensor in Surveyor’s Wheels for Measuring Distance

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Nov 7, 2020

Sensors for Window Sun-shade Shutter Control

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Nov 6, 2020

Reed Sensors in Automobile Power windows

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Nov 7, 2020

Reed sensors to control Automobile Sun-roofs

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Nov 7, 2020

Reed switches in Petrol and Diesel Pumps

Reed switches in petrol and disel pumps Fuel Nozzle Petrol and diesel pumping stations are explosive environments where a minor mistake could cause a great big fire. Reed Continue reading ->

Nov 7, 2020

Magnet sensors in Bicycle Speedometers

Reed switches in bicycle speedometer Bicycle Speedometer Fitness is always in, and people who exercise always need feedback on how many calories they have burnt, or how Continue reading ->

Nov 7, 2020

Magnet Sensors in Treadmills

Reed switches in treadmill Treadmill Magnet Sensors find a few applications in treadmills for speed and gradient sensing. The speed of the belt is determined by Continue reading ->

Nov 7, 2020

Reed Switches and Reed Sensors in Digital Fishing Reels

Reed switch usage in electric fishing reel Fishing Gear Digital Fishing reels are an improvement over the standard, well-proven fishing reel and rod used for winding and stowing Continue reading ->

Nov 7, 2020

Reed sensors for Tamper-proofing Electricity Meters

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Nov 6, 2020

Magnet Sensors in Anemometers

Reed switches in anemometer Anemometer An Anemometer is an instrument used to measure wind speed. Spinning cup anemometers are measure wind speeds and are part of Continue reading ->

Nov 6, 2020

Flow Meters for checking Lake currents

Reed switches in flow_meter Lake Current Meter Underwater currents in lakes and other water bodies are caused by various factors such as pressure gradients due to Continue reading ->

Nov 7, 2020

Magnet sensors in Anti-lock braking system (ABS)

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Nov 7, 2020

Magnet sensors for Automobile Cruise Control

Reed switches in speedometers Cruise Control Cruise Control automatically controls the speed of a motor vehicle by adjusting the accelerator so that the driver need Continue reading ->

Nov 7, 2020

Magnet sensors in Satellite dish position sensing in the DTH industry

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Nov 6, 2020

Magnet Sensors in Fluid Metering

Water meter Fluid Meter In most large cities, utility companies or closed communities run piped Water and Liquefied Petroleum Gas, LPG, to all Continue reading ->

Nov 7, 2020

Reed switches and Reed sensors in Spirometers

Spirometer Spirometer for Lung Function Testing A Lung function test or Pulmonary Function test, PFT for short, is a system to evaluate the Continue reading ->

Nov 6, 2020