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Which parameters must be checked to match encoder card to an existing encoder ?

Published date: 12 March 2019

Here is the list of criteria that must be checked.

1. Encoder mechanical speed range. Check encoder max speed if it is equal or greater than max operational speed of shaft encoder is conencted to
2. Max output frequency from encoder must cover operating speed range of its shaft with respect to number or pulses per revolution. E.g. Motor shaft will be operated at speed range 0-1500rpm that gives 0-25 turns per second. Considering encoder with 1024 pulses per revolution, encoder signals must be able to carry frequency 25*1024=25.6 kHz. Typical values that encoders can manage are 200-300kHz
3. MAx frequency of signals that encoder card must be able to process. Use the same calculation as above. Ecnoder card as well must be able to process this frequency.
4. Interface. Each encoder has interface that defines the level of output signals. The most often is RS422 (also called TTL or line driver) . Other possible are HTL (usually push-pull or open collector), SINCOS, SSI, ENDAT, RESOLVER. Note that our VSDs (ATV930, 340) depending on option card used, suport RS422, HTL, SINCOS, SSI, ENdat. The best to check which signals are provided by encoder and if there is adequate input on encoder card. Not all signals are necessary. for example, for TTL and HTL at least A and B signals are needed. 

5. Supply voltage. Check encoder datasheet which supply voltage is needed. Ususally encoder manaufacturer offers wide range of supply voltage. Typical supply voltage delivered by our drives or option cards are 5V, 12V, 15V, 24V
6. Consumption in supply voltage by encoder. Check encoder datasheet if its consumption is less than max current the ATV or option card can deliver. 
7. Current drawn by encoder card in the signal. This can also be limitation, for example our RS422 card VW3A3420 has input impedance 121 Ohms, that means for high signal level (5V in RS422, 12 or 24V for HTL depending on suply voltage used) it consumes 41mA (RS422). VW3A3434 has input impedance 2kOhm, so current drawn at 12V suply is 6mA, at 15V is consumption 7.5mA, at 24V 12mA
8. Number of pulses (RS422, HTL) or bits (SSI) or SINCOS lines (SINCOS) per revolution if it matches possible setting. Create offline configuration in Somove and check which values can be set. In general 512, 1024, 2048 are most used and are OK.


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