How to Select an Encoder

Portescap standard catalogue encoders feature only digital incremental encoders, using different technologies (optical, magnetical hall sensor, magneto-resistive). Such encoders provides digital square signal ouputs in quadrature (usually called channels A and B), so that the rotor position, the rotor speed, and the direction of rotation can be determined. Some of them also features additional output signals, such as an index ouput which provides a pulse once per revolution, in order to define a reference position; or such as complementary signals A\, B\, I\ enabling elimination of interferences when a long harness is used.

The main parameters to take into account when selecting an encoder are:

Resolution

We defined it by the number of lines (pulses) per revolution (1 line (pulse) = 4 counts)

Accuracy

The main contributor is the mechanical error, which is the maximum angle between the position measured by the encoder and the real/actual position of the rotor, expressed in mechanical degree.

Phase shift / duty cycle

It will create, for instance, noise on the measurement of the speed.

Output signals

Depending on the encoder type, you might have an index, or complementary outputs (line driver).

Maximum operating speed

This limitation is defined by the maximum frequency response of the encoder electronic itself. This might be a point of concern for high speed application / high resolution encoder. The motor speed can be derived from the count frequency using the formula: N = f x 60 / CPR where:
N = Motor speed (revolution per minutes)
f = Encoder counts frequency (Hz)
CPR = Number of counts per revolution (4 times the number of lines/pulses per revolution)

Environment

Package size of the encoder, the temperature humidity and pressure conditions which might create condensation, dusty environment, electromagnetic perturbated environment, etc; might guide you to select the most suitable type of encoder.