Encoders are specified backwards when the mechanical shaft is ordered first and the signal is left as encoder, 1000 pulses. Write the electrical interface the drive can read, then the mechanics, then the washdown or the oil.
Electrical interface
Incremental outputs may be open collector, push-pull, or differential line driver. Differential is the one that survives a long cable and a noisy cabinet. Absolute encoders speak a protocol the drive must list by name. A protocol that is close is not the protocol. Supply voltage is 5 V or 10-30 V on many industrial parts. Pick the one the drive provides. Add the cable length, because the output type and the cable are one decision.
- Incremental resolution, or absolute protocol and bits.
- Output type and supply voltage.
- Shaft, hollow bore, or ring, with the diameter.
- Connector pinout or a flying lead with colors defined.
- IP rating and temperature if it is outside the cabinet.
| Need | Specify | Failure if omitted |
|---|---|---|
| Position at power-up | Absolute, protocol named | A homing move you cannot do |
| Long cable | Differential outputs | Counted noise |
| Drive input | Voltage and the levels the drive lists | A burnt encoder or no counts |
Sample check
Confirm the label resolution and the supply. Power it from the drive supply you will use, not from a random bench voltage. Turn the shaft and see counts in the drive, including direction. Confirm the connector key. Do not describe this as a safety function unless the encoder and the drive are specified as one. A standard incremental encoder is a motion sensor, not a guard.
What to lock on the order
Draw the encoder with its supply voltage, output type, and counts or protocol on the electrical sheet, and the bore or shaft on the mechanical sheet, with the same part number on both. Cable length and whether the cable is flexing belong on the electrical sheet too. A drag-chain cable is a different part from a static pigtail. Ask the drive maker which inputs are enabled in the parameter set you will ship, and buy the encoder that matches those inputs. Differential signals and a single-ended input can be made to work and then fail in noise. Specify the connector so the spare is plug compatible. At incoming inspection, power the encoder from the drive, confirm direction, and confirm the marker pulse if you use one. Label the sample with the drive parameter file name. A later drive firmware change that expects a different count is a controlled revision, not a warehouse swap.
Questions buyers actually ask
Incremental or absolute?
Incremental tells you motion after you find a reference. Absolute tells you position at power-up. Buy absolute when the machine cannot rehome.
What is a pulse count?
It is the resolution per revolution, and quadrature multiplies how the drive counts it. Write the counts the drive expects.
Does the connector matter?
Yes. Pinout and supply voltage are field mistakes. A 5 V encoder on 24 V is destroyed, not slightly inaccurate.