Schneider/SoMachine - Issues with capturing prox sensor signals.

stn99nts

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Feb 2017
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Processor: Schneider M241
Software: SoMachine 4.3

I am trying to capture the RPM of a shaft using a prox sensor. The shaft has two cams on it that trigger the sensor twice per 1 shaft revolution.

I am basically recording how many times the prox pulses in the span of 3 seconds then doing some math to convert that into rotations per minute.

While I’m certain that my math is correct, I am having issues getting an accurate value once I get past 700RPM.

I am using input I0, which is considered a high-speed input, yet at 880 RPM (verified with rotation gun) it seems to get stuck at 690RPM.

I’ve tried configuring the input parameters in the devices tree in every way possible, but I still can’t get it to register proper values once I spin the machine faster than 700RPM.

Should I be using one of the HSC function blocks to capture this? I don’t really see why I would need to use HSC for anything since the input is good for a few kilohertz and I’m running no more than 15 Hz. Though I may be totally wrong in this assumption.

I should mention that we used an AB HSC card to capture these readings on a prior project and it worked fine. The customer decided to go with a Schneider processor this time around to save $$$.

Any help would be greatly appreciated. Thanks in advance.
 
What is the on/off response time of your sensor, I would suggest using only one flag for the sensor and making it larger maybe 180 degree of the rotation and doing the math for 1 pulse per revolution, Just because your high speed in put can accept a fast pulse doesn't mean your sensor can provide it. Just a Thought
 
These are the same sensors that we have used previously on the machine using the AB HSC card.

Forgive me, as I'm new to SoMachine, but where do I check the input card detection time?
 
Processor: Schneider M241
Software: SoMachine 4.3

I am trying to capture the RPM of a shaft using a prox sensor. The shaft has two cams on it that trigger the sensor twice per 1 shaft revolution.

I am basically recording how many times the prox pulses in the span of 3 seconds then doing some math to convert that into rotations per minute.

While I’m certain that my math is correct, I am having issues getting an accurate value once I get past 700RPM.

I am using input I0, which is considered a high-speed input, yet at 880 RPM (verified with rotation gun) it seems to get stuck at 690RPM.

I’ve tried configuring the input parameters in the devices tree in every way possible, but I still can’t get it to register proper values once I spin the machine faster than 700RPM.

Should I be using one of the HSC function blocks to capture this? I don’t really see why I would need to use HSC for anything since the input is good for a few kilohertz and I’m running no more than 15 Hz. Though I may be totally wrong in this assumption.

I should mention that we used an AB HSC card to capture these readings on a prior project and it worked fine. The customer decided to go with a Schneider processor this time around to save $$$.

Any help would be greatly appreciated. Thanks in advance.

By looking at the hardware manual there is an input filter setting that affects the CPU's detection of the signal.
The turn on and turn off times of those inputs are 50 microseconds (2 microseconds for HSC configured input) + filter time. I would look at that setting and lower it if it is high. I would think that downloading the hardware configuration will be required everytime that setting is changed.

The above is based on the hardware manual of an M241 CPU not an input card.
 
Last edited:
There are actually two different filters depending on the function associated with the input so if the input is configured for latch, even or HSC then bounce filter is relevant otherwise integrated filter is relevant. Again this is from the hardware manual.
Going by memory Chud is the guy who know most about these PLCS, hopefully he will see this thread.
 
What is your PLC scan time.
If you have located your input to normal scan on program side, input counting can't be faster than that.
Make program section for counting to independent POU and call it by (interrupt input) or as fast as is possible on program POU calls
 

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