Reed Switches Being Replaced by Optical Encoder

By Admin on Tue 05 December 2017 in Water Meter FAQ's and Information

Following changes in the the latest version of the Measuring Instrument  Directive (MID), Arad have phased out the use of reed switches to produce pulse outputs on their larger water meters and those meter used for billing with a new solid state solution - the Optical Encoder. Multijet meters, which are generally used for in-house process control retain the use of the traditional reed-switch..



The optical encoder unit is compatible with any Arad water meter that is equipped with a rotating optical disc, one semicircular half of this disc is black the other half is gold-coloured.  The optical encoder uses  an infra red LED to illuminate the disc, IR pulses reflected off the disc as it  rotates are detected by sensors and the optical encoder’s internal logic interprets these optical pulses to produce a stream of electrical pulses.



The optical encoder is protected from electromagnetic interference and from sunlight.  It incorporates a microprocessor that detects rotation direction, counts disc revolutions, and generates output pulses based on the sensor readings.


The OE output is an open drain, unlike the reed switch used in previous pulse output meters the output of the OE is sensitive to polarity, the wires are colour coded.


Typical connections to a counter



The optical encoder incorporates protection from false reading caused by vibration of the optical disc.


The Optical Encoder is powered by an internal lithium primary battery which offers long service life of typically ten years.