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S7 1200 HSC counts to pulses/sec

Created by: bennyk@37.com at: 2/3/2012 10:05 PM (4 Replies)

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2/3/2012 10:05 PM	Rate (0)
bennyk@37.com Posts: 5 Rating: (0)	Hello, I have a HSC configured to count frequency on my S71200 PLC. The max average measuring period i can have is 1 sec. I am not happy with the accuracy. I want to now count the actual number of pulses over a longer period (maybe 10sec) and convert this value to frequency (pulses per second). I expect this involves a timer etc but i am not sure where to start. Can anyone advise me on a program that can do this task? thanks
bennyk@37.com Posts: 5 Rating: (0)
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2/3/2012 10:16 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 11/5/2024 Posts: 15385 Rating: (2443)	bennyk@37.com Hello, I have a HSC configured to count frequency on my S71200 PLC. The max average measuring period i can have is 1 sec. I am not happy with the accuracy. I want to now count the actual number of pulses over a longer period (maybe 10sec) and convert this value to frequency (pulses per second). I expect this involves a timer etc but i am not sure where to start. Can anyone advise me on a program that can do this task? thanks The pulses coming into the PLC, what do they look like on an O-Scope? Do they have any type of inconsistency that may cause the HSC not to detect either an on or off state? I ask because the HSC should be considerably more accurate than using a timer and counting pulses manually. Maybe a screenshot of the hardware configuration for your HSC might help in the event it is not a noise or induced signal type problem.
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2/4/2012 1:20 PM	Rate (0)
bennyk@37.com Posts: 5 Rating: (0)	Hello, I have a HSC configured to count frequency on my S71200 PLC. The max average measuring period i can have is 1 sec. I am not happy with the accuracy. I want to now count the actual number of pulses over a longer period (maybe 10sec) and convert this value to frequency (pulses per second). I expect this involves a timer etc but i am not sure where to start. Can anyone advise me on a program that can do this task? thanks The pulses coming into the PLC, what do they look like on an O-Scope? Do they have any type of inconsistency that may cause the HSC not to detect either an on or off state? I ask because the HSC should be considerably more accurate than using a timer and counting pulses manually. Maybe a screenshot of the hardware configuration for your HSC might help in the event it is not a noise or induced signal type problem. Hello the pulse width themselves vary as the speed changes. i.e at lower speeds the width of the positive pulses are wider, as the speed increases the pulse widths reduce. the reason for this is because the pulse sensor is basically a proximity switch. therefore at lower speeds the switch is closed for a longer period thus giving a wider pulse width. I am stuck with this sensor and must use it as the signal source. I can send on a screen shot of the hardware configuration in two days when i am back. the HSC config is fairly basic. i have simply enables the HSC and selected frequency count at 1sec period. i am wondering if i change the "single phase" setting to "AB quadrature" in order to increase accuracy. However i only have one input into the PLC that has th pulse signal. I was thinking if i inreased the measring period to over 1sec (as is limited in the frequency setup) to a wider period with the count then i would increase accuracy? it is important that i increase the accuracy. at the moment the frequency measrument will measure e.g 15....16......17.....18Hz etc. i would like to measure intermediate values i.e 15.4.....16.8...17.2....18Hz etc. thanks for the reply reards Brendan
bennyk@37.com Posts: 5 Rating: (0)
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2/12/2012 11:50 AM	Rate (0)
Przemos169 Posts: 8 Rating: (0)	Hello, when you want high accuracy and measurment period greater than 1s, you can use HSC in counter mode and use "cyclic interupt", maximal period measurment is 60s. You have to only read the value from HSC in ID1000 to your main program where you change this value in to frequency. Regards Przemos169
Przemos169 Posts: 8 Rating: (0)
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2/12/2012 2:13 PM	Rate (0)
bennyk@37.com Posts: 5 Rating: (0)	Hello, Yes thanks. thats exactly what i done. I have the program up and running with a week and the accuracy seems to be very good. regards, Brendan
bennyk@37.com Posts: 5 Rating: (0)
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