We have a problem we have been running into with a recent project. We are currently using 2 Micro-E linear digital encoders with .05um resolution and 1.8MHz output freq, hooked into a NI 9411 card in a cRIO 9075. The encoders use TTL logic, wired single-ended. I created a basic FPGA VI that reads the digital signals and increments or decrements 2 separate counters (1 for each encoder). This VI is attached below. The two counters at the bottom of the loop are the problematic ones.
The count successfully increments and decrements when the encoder readhead is slid up or down the tape scale. Our problem is that our count randomly "flutters" when the encoder readhead is sitting completely stationary. Sometimes it's a flutter of only 1-10 counts, + or -. Then randomly it will shoot up hundreds or thousands of counts, then stabilize again, then flutter again, rinse, repeat.
We originally thought that the encoders, being so sensitive, were the problems, but after a series of scopes and tests with Copley equipment both differential and single-ended, we have come to the conclusion that the encoder is good and the problem lies somewhere in the National Instruments equipment or software.
We also wired a Renishaw 32768 count rotary encoder into the 9411 in the same ports as the Micro-E encoders to test the validity of the LabView code, and it worked flawlessly. Something with these Micro-E encoders and Nat
Any insight into what the problem could potentially be?