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Frequency metering S7-1200

Created by: SukramB at: 7/11/2014 7:49 AM (10 Replies)

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7/11/2014 7:49 AM	Rate (0)
SukramB Posts: 4 Rating: (0)	Hi all, I am trying to set up a HSC to monitor the frequency from a pulse generator with poor success. So far I have set up the HSC in the CPU (see attached), and I am trying to move the value from %ID1000 to a variable using a MOVE instruction. Although I can see the pulses on the CPU input I get no frequency response, %ID1000 and the other variable stays firmly at 0. Do I need to do something more, like using the CTRL_HSC? The PLC is a 1214C, I am using TIA Portal v12 Basic. Attachment hsc_dump1.jpg (1113 Downloads)
SukramB Posts: 4 Rating: (0)
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7/11/2014 8:36 AM	Rate (0)
William_B Posts: 5225 Rating: (1196)	SukramB Hi all, I am trying to set up a HSC to monitor the frequency from a pulse generator with poor success. So far I have set up the HSC in the CPU (see attached), and I am trying to move the value from %ID1000 to a variable using a MOVE instruction. Although I can see the pulses on the CPU input I get no frequency response, %ID1000 and the other variable stays firmly at 0. Do I need to do something more, like using the CTRL_HSC? The PLC is a 1214C, I am using TIA Portal v12 Basic. Hi there. Please review the PDF attached. See if there is something you have missed. Make sure the Frequency Measuring Period is set at an acceptable update rate. Remember.. a count is shown of pulses captured in that period. I do not think it is needed to use HSC_CTRL instruction block. But it would not hurt calling the block. You could use the HSC as a counter and do the extraction of the frequency yourself. Please see this topic.. [LINK] Look at 6/28/2014, 3:51 PM Follow the discussion from the 2nd page for more relevant info. Hope this helps you. w Attachment Quick & Dirty_HSC for frequency indicator.pdf (1677 Downloads)
William_B Posts: 5225 Rating: (1196)
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7/11/2014 4:22 PM	Rate (0)
SukramB Posts: 4 Rating: (0)	Hi, Very helpful, thank you! Error found and corrected! Have a pleasant weekend Markus
SukramB Posts: 4 Rating: (0)
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8/4/2014 6:21 AM	Rate (0)
vasr9 Posts: 3 Rating: (0)	I am in a similar problem. Could you explain what was the error and how you fixed it? I am able to see values, but it is not the real frequency, so maybe I am missing a step.
vasr9 Posts: 3 Rating: (0)
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8/4/2014 1:55 PM	Rate (0)
SukramB Posts: 4 Rating: (0)	vanessadriana I am in a similar problem. Could you explain what was the error and how you fixed it? I am able to see values, but it is not the real frequency, so maybe I am missing a step. I am not at work at the moment, so I cannot post any screenshots to help you, but in my case, I made the following fixes: - The two channels from my speed sensor are the same but with a90 degree offset, so I had to set it up for "Single phase" since I couldn't get it working with both channels. - Doing that I forgot to physicly remove the wire from channel two, which in single phase mode is used as reset, making my readings very weird. - Finally I had to change the measuring period to 1 s, I tried with a lower value but since the frequency is quite low (the speed sensor gives 200 pulses/revoution and the wheel rotates with a maximum speed of 3 revolutions/second in this application), the readings were pending up and down in low speeds. I then moved the value from ID1000 to an INT to be able toconvert into a km/h-speed. Hope you can get something out of it, otherwise post again! Markus
SukramB Posts: 4 Rating: (0)
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8/4/2014 4:42 PM	Rate (0)
vasr9 Posts: 3 Rating: (0)	Thanks for the answer. But I am still in doubt if the readings I am getting are wrong. Please help me if I am wrong. I set up the HSC1 (as seen in the first image, sorry it's in spanish). Frequency, single phase, internal control, 1sec period I used one of the outputs to measure a known frequency (because I do not have the sensor with me available). This can be seen in the second image. As you can see, the period is 200ms, which is 5Hz. But in the readings, as you can see in the 3rd image, I am getting between 44 and 53. (I am multiplying it by 60 because I was trying to get RPM) Obviously if I divide by 10 I would get the desired value, but I don't understand why I would do that. Maybe I am missing something? Attachment Capturas.pdf (810 Downloads)
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8/4/2014 10:31 PM	Rate (0)
William_B Posts: 5225 Rating: (1196)	¡Hola! The images fills me with questions. It does not make sense that you ask for 1s sampling and get 10s sampling. The code you shown us, is the only code running on the PLC, right? Please could you force TIA to compile and rebuild all the blocks, then reload the PLC and check again. As a bonus step you could even load an empty project into the PLC before you reload the PLC with your test program. I understand you have relays for outputs, but you should be able to generate your pulse using the PWM function (hardware configuration). Just make sure you have a low frequency rate. This method should give you a consistent pulse output.. if wanted to change something in your test method. If you are willing to leave us your test program we could see if we can identify the issue by loading the code into another CPU.
William_B Posts: 5225 Rating: (1196)
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8/4/2014 10:33 PM	Rate (0)
SukramB Posts: 4 Rating: (0)	I can't see any errors in the setup, so it should work in theory? Perhaps the hardwiring between output and input is giving some problems, do you have any other form of frequency generator to try with?
SukramB Posts: 4 Rating: (0)
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8/4/2014 10:51 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 11/15/2024 Posts: 15402 Rating: (2443)	SukramB I can't see any errors in the setup, so it should work in theory? Perhaps the hardwiring between output and input is giving some problems, do you have any other form of frequency generator to try with? So many functions available with DC outputs like PTO / PWM are not available for RLY outputs. If you have relay outputs and want to measure input pulse frequency, remember your pulse amplitude must meet the "on" or "1" voltage requirement to be counted. A 10VDC pulse is likely to be ignored all the time.
	science guy
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8/5/2014 8:25 AM	Rate (0)
vasr9 Posts: 3 Rating: (0)	Well, I measured the input V and it is in 25V when the logic is in "1". So that is not the problem. On the other hand, I configured the HSC in Counting mode, and to my surprise, I also get the value multiplied by 10! This means the counter goes something like this 10, 21, 33, 42, 55, 63... and on and on with each pulse. I am not compiling nor loading any other logic into the PLC. In the following link is the project that I am uploading to the PLC https://app.box.com/s/2i0oe7ru0h2b9mez7nrr
vasr9 Posts: 3 Rating: (0)
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