Not getting the right count from quadrature encoder

I'm using a BEI (H37C-SS-2356-ABC-28V/V-SM16)quadrature rotary encoder (A/B) connected to the high speed inputs (A phase=X0, B phase=X1) of a FX1S Mitsubishi PLC. I'm using the high speed counter C251 (always enabled with M8000=PLC in RUN) to measure the feed length of a stamping machine. The encoder has a resolution of 2356 pulses/rev, so that each pulse represents 0.001" of material fed by the 3/4" feeding rolls (Diameter=Circunference/pi=2356/3.14=750 mils).
The problem I have is that instead of getting, for example, 1000 counts in the encoder per inch I'm getting 255. The count I get every cycle is 3.92 times less than I expect (is constant every cycle), even at low speed, or at different feed rates, but I need to be able to measure 0.001", that means, 1 count.
Any idea why I am getting less pulses every time?
Any test I can do to find the problem?

It's like you got a 600 count encoder instead of a 2356 count encoder.

Is this a new application or has it worked before?

Before it has an electronic board to do the same, but it is damaged. We replaced the encoder (same part number) to check if this was the problem, but it didn't work, so we decided to use a PLC to read the encoder. Actually the 2356 in the part number indicates the resolution.

The part number indicates that this is a custom encoder. 2356 sounds like a strange number for an encoder, have you considered one of BEI's omnicoders?
http://www.beiied.com/omnicoder/index.html
With one of these any resolution up to 10,000 PPR can be programmed.

The multiplier you listed (3.92 ) also doesn't sound like it is just a counter card problem. Some counter cards will let you multiply the PPR times two or four.

gleon said:

Before it has an electronic board to do the same, but it is damaged. We replaced the encoder (same part number) to check if this was the problem, but it didn't work, so we decided to use a PLC to read the encoder. Actually the 2356 in the part number indicates the resolution.

Click to expand...

Can you put the original encoder back in service?

Perhaps the replacement encoder is mis-marked...

I'm going to disconnect mechanically the encoder from the machine and then manually rotate it to see how many counts per one revolution I get. When I tested this before installing it in the machine I just saw that I was reading the encoder and that I was getting the same values in the same positions, but I didn't pay attention to how many counts per revolution I got. If I find the old encoder I can try that too. (Hope the technicians didn't throw it away)

I've read about this omnicoders with programmable resolution. I'm using this encoder because I already had it here as a spare part for the machine, but it is a good idea to consider an omnicoder as a future spare part for the one I already have (if I can read the right value someday).