I'm using a 9401 module in a 9188 chassis to measure position of a shaft in 1E6 count/rev. The signal is an emulated AQuadB out from a Kollmorgen AKD servo drive. My problem is that when the drive is enabled, the noise it makes it being picked up as extra positive counts by the 9401. The drive has RS485 outputs, but my cable length is short and well shielded, so I thought it would work okay. It's wired like this:
9401 CTR1 channel
A+: 9401 pin 20
B+: 9401 pin 23
GND: 9401 common
Cable Shield: 9401 common
Is this occuring since the encoder signal is differential, or is my grounding/shielding not correct? If I disable the encoder entirely the 9401 picks up a solid zero. Should I use some sort of converter from the RS485 to TTL?