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

surveyor wheel Surveyor's Wheels use a reed switch mounted on the rim and a ring magnet...Continue reading ->

Sensors for Window Sun-shade Shutter Control

window shutter With reed sensors mounted near the rotating shaft mechanism of these motors, and multi-pole...Continue reading ->

Reed Sensors in Automobile Power windows

Car power window The motor which drives the glass up or down has a multi-pole ring magnet...Continue reading ->

Reed sensors to control Automobile Sun-roofs

automotive sunroof An automotive sun-roof, usually made of tinted glass, is a movable panel that can...Continue reading ->

Reed switches in Petrol and Diesel Pumps

Reed switches in petrol and disel pumps Petrol and diesel pumps use reed switches to sense if the nozzle has been...Continue reading ->

Magnet sensors in Bicycle Speedometers

Reed switches in bicycle speedometer A magnet can be attached to one of the spokes in the wheels, and...Continue reading ->

Magnet Sensors in Treadmills

Reed switches in treadmill The speed of the belt is determined by positioning a reed sensor near the...Continue reading ->

Reed Switches and Reed Sensors in Digital Fishing Reels

Reed switch usage in electric fishing reel Electric fishing reels are equipped with reed sensors which generate pulse on rotation of...Continue reading ->

Reed sensors for Tamper-proofing Electricity Meters

tamper proof electricity meter To tamper proof Electricity meters, Reed Sensors are placed near the front cover of...Continue reading ->

Flow Meters for checking Lake currents

Reed switches in flow_meter Reed Switches are used in flow meters to calculate volume of liquid. Flow meters...Continue reading ->

Magnet Sensors in Anemometers

Reed switches in anemometer Spinning cup anemometers are fitted with magnets and as the wind blows, a reed...Continue reading ->

Magnet sensors in Anti-lock braking system (ABS)

Reed switches in ABS control system In ABS control, the onboard electronics needs to apply differential hydraulic pressure to each...Continue reading ->

Magnet sensors for Automobile Cruise Control

Reed switches in speedometers A multi pole ring magnet can be attached to the speedometer actuating shaft, and...Continue reading ->

Magnet sensors in Satellite dish position sensing in the DTH industry

satellite dish While tuning satellite dishes to various providers, the motor is turned until a clear...Continue reading ->

Magnet Sensors in Fluid Metering

Water meter To make an existing analog fluid meter generate digital output readings that can be...Continue reading ->

Reed switches and Reed sensors in Spirometers

Spirometer Reed Switches help measure the volume of air intake and the time in a...Continue reading ->