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Flexible motor speed measurement

02 May 2013

Motor speed is usually measured by means of an internal sensor bearing or an optical encoder with fixed pulse counts, whereby a separate sensor or code disc (code wheel) is required for each pulse count. This has a negative effect on flexibility and storage, says Variohm EuroSensor, UK distributor for Contelec.

When sensor bearings are used, the electronic unit is frequently not rugged enough and so is susceptible to external causes of malfunction. There is also the time involved in servicing internal sensors and consequent loss of availability in the event of a sensor malfunction.

The use of optical encoders and encoder modules requires precision installation, which in turn demands precision bearings and extremely accurate alignment of the code disc to the optical module. However, the temperature fluctuations which are common in motor operation cause material expansion in encoder components in excess of the tolerances for optical encoders, bringing the risk of failure.

Also, if production of a particular sensors ceases and is no longer supported, users are faced with the high cost and time involved in finding an alternative.

To tackle this problem, Contelec has launched an innovative sensor concept that makes use of a slim external sensor to measure the speed of the main shaft – without any physical contact between the magnetic actuator and sensor unit. All that is needed to attach the magnetic actuator is to tap a hole in the main shaft.

The sensor unit itself is attached to the reverse of the motor or to the fan housing and aligned. The shape of the sensor has been designed to have a negligible influence on the air flow.

To simplify installation, Contelec supplies pre-configured sensors. A broad range of pulse counts may be configured by keeping always the same magnetic actuator.