kamenges
Member
One of the guys I work with is on an install. He is attempting to read a signal off a Red Lion RPGC 100 ppr pulse generator with an AB 1756-HSC module. He is getting more counts than he expects to get. This pulse generator has a 1 foot circumference wheel and the machine is running up to 750 FPM.
At this point we believe the issue is 'noise' on the pulse generator signal. We have an o-scope here that he is taking with him tomorrow to scope the input. However, if it is noise we are a little stuck. The 1756-HSC has a filter you can use. However, it has a fixed cut-off frequency of 70 Hz. That's too slow for us. We are in the area of 1250 pulses per second.
I'm trying to get a jump on solutions if it does turn out to be noise. Does anyone know of a fre-standing signal conditioner designed specifically for cleaning up encoder noise? BEI makes something that performs an internal quadrature decode that cleans up channel jitter. I don't have a quadrature encoder, however. That is my fall-back at this point. I'm thinking about a high pole count low pass Bessel filter but that may introduce as many issues as it solves.
Also, can anyone tell me why Rockwell would put a frequency selectable low pass filter in the 1794-VHSC but not put the same thing in the 1756-HSC? One would think the 1756- HSC, being part of the flagship platform, would have all the bells and whistles.
Thanks,
Keith
At this point we believe the issue is 'noise' on the pulse generator signal. We have an o-scope here that he is taking with him tomorrow to scope the input. However, if it is noise we are a little stuck. The 1756-HSC has a filter you can use. However, it has a fixed cut-off frequency of 70 Hz. That's too slow for us. We are in the area of 1250 pulses per second.
I'm trying to get a jump on solutions if it does turn out to be noise. Does anyone know of a fre-standing signal conditioner designed specifically for cleaning up encoder noise? BEI makes something that performs an internal quadrature decode that cleans up channel jitter. I don't have a quadrature encoder, however. That is my fall-back at this point. I'm thinking about a high pole count low pass Bessel filter but that may introduce as many issues as it solves.
Also, can anyone tell me why Rockwell would put a frequency selectable low pass filter in the 1794-VHSC but not put the same thing in the 1756-HSC? One would think the 1756- HSC, being part of the flagship platform, would have all the bells and whistles.
Thanks,
Keith