Standard cables in use by motors and sensors might just have a length of 30 cm up to 3 m. Sometimes this is not long enough especially if controllers are installed in a cabinet of a machine which might be placed some meters away or even in another room.

There is no general answer concerning the maximum cable length. A cable length of up to 10 m can be handled without any problems if some special measures are taken into account. Even cable lengths up to 50 or 100 m have been successfully in use if anything is installed in a perfect way and the signal quality is checked and confirmed during initial commissioning.

Special measures to think about in case of long cable lengths

Quite often the first spontaneous thought might be that the signal’s voltage drop on long wires might be the critical point. In fact this is not the truth because sensor signals often just have to fulfill the TTL specification which accepts a “High” signal already at a voltage level above 2.1V. The required signal level is specified in the “Hardware Reference” of the maxon controllers in the chapters about the encoder and hall sensor inputs.

1) Sensor’s supply voltage

Encoders typically have a tight tolerance concerning the supply voltage. In case of a 5V +/-5% specification this means that at least 4.75V has to be present at the encoder’s supply voltage input to ensure its operation. The voltage drop of long cables can get critical from the supply voltage’s point of view. If the supply voltage is not sufficient, the sensor signals will not be present, wrong, or sometimes missing. The root cause of missing pulses is often the supply voltage and not the signal level like expected. Therefore it is important to ensure that the specified supply voltage is present at the encoder’s connector. This can be improved by using thicker wire gauges inside the cable. Actually such thicker wires are just required for the supply voltage and GND wire. The voltage drop of the sensor wires is not so critical like mentioned above.

The drawback of generally thicker wires is that these make cables less flexible, heavier, and more expensive. Cables with mixed wire gauges are very special designs and even more expensive. There is a simple solution to overcome these drawbacks:

Use more than one wire for the supply and GND

Buy a cable with more wires than actually required, e.g. a cable with 10 or 12 wires instead of just 8 wires typically required by an encoder. Use 2 – 3 wires for the supply and GND. Such cables are standard, most cost-efficient, and still are more flexible than a cable with thicker wire gauges.