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PID 3 step error in setpoint

Created by: jinga at: 6/26/2014 4:18 PM (5 Replies)

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6/26/2014 4:18 PM	Rate (0)
jinga Posts: 26 Rating: (2)	Hi! I have built a simple program to control a mixing valve using 3 step PID block, however I cannot make it work. I call this blok in a cyclic interrupt executing for 60s. I manually insert the setpoint on HMI panel (example 30°C), but each cycle it goes to 2°C! Why is that happening? I'm attaching a screenshot of the block I'm using. The outputs are two digital outputs which make the valve open or close. Valeria Attachment Immagine 1.jpg (239 Downloads)
jinga Posts: 26 Rating: (2)
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6/26/2014 4:35 PM	Rate (0)
Kelu Posts: 88 Rating: (12)	Hello, Are you sure your setpoint "MD7" isn't write anywhere else in your program or in HMI?. Make a cross reference on it.
Kelu Posts: 88 Rating: (12)
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6/26/2014 4:56 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 1/17/2025 Posts: 15541 Rating: (2465)	Try changing your MD7 to something with an even number, like MD8.
	science guy
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6/26/2014 5:29 PM	Rate (0)
jinga Posts: 26 Rating: (2)	ok, even number trick worked, but I have another problem...the outputs are always both FALSE, when set>input and when set<input...how is it possibile?
jinga Posts: 26 Rating: (2)
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6/26/2014 5:42 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 1/17/2025 Posts: 15541 Rating: (2465)	jinga ok, even number trick worked, but I have another problem...the outputs are always both FALSE, when set>input and when set<input...how is it possibile? Are you providing feedback or is that still set to 0
	science guy
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6/26/2014 6:05 PM	Rate (0)
jinga Posts: 26 Rating: (2)	huggy_d1 jinga ok, even number trick worked, but I have another problem...the outputs are always both FALSE, when set>input and when set<input...how is it possibile? Are you providing feedback or is that still set to 0 My valve does not have a feedback signal, only 2 digital signals for open/close, so I haven't set a feedback...From the sample program downloaded from support section I understood I could use PID even without feedback...am I wrong?
jinga Posts: 26 Rating: (2)
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