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Compensated setpoint

Created by: Jerid at: 10/14/2017 8:28 PM (9 Replies)

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10/14/2017 8:28 PM	Rate (0)
Jerid Posts: 3 Rating: (0)	Hi I need some help with compensated setpoint. I have PT100 sensor in exhaust air duct. From that value i need to get setpoint for supply air duct. Example, if exhaust temperature is 24, supply needs to be 18, and if exhaust is 18, supply 24, like linear curve. is this possible, and what program modules i need?
Jerid Posts: 3 Rating: (0)
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10/14/2017 8:42 PM	Rate (0)
ixo65 Grandmaster Joined: 12/18/2014 Last visit: 9/16/2025 Posts: 35964 Rating: (4502)	Too little information. How should the setpoint be passed on, with which signal? And to which control device? 0 - 10 V? 0 / 4-20mA?

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10/14/2017 8:43 PM	Rate (0)
Diniz_ Bronze Member Joined: 7/2/2016 Last visit: 7/6/2025 Posts: 120 Rating: (29)	Hi Jerid, you need a ratio control strategy, you can probably do this with math blocks on LOGO! ill try some examples for you.
	hope this help, if it was helpful please rate the post! ---- BR, Diniz Carvalho
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10/14/2017 8:46 PM	Rate (0)
Jerid Posts: 3 Rating: (0)	Hi Setpoint will be passed to PI control. PI control controls 2way valve.
Jerid Posts: 3 Rating: (0)
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10/14/2017 8:51 PM	Rate (0)
ixo65 Grandmaster Joined: 12/18/2014 Last visit: 9/16/2025 Posts: 35964 Rating: (4502)	These are still not enough information. For a PI controller, you can only set the setpoint for one point. So, where is the setpoint? In the middle between 18 °C and 24 °C?

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10/14/2017 8:59 PM	Rate (0)
Jerid Posts: 3 Rating: (0)	example, if exhaust air temperature is 23.5 , supply air temperature needs to be 18.5 but if exhaust air temperature is 22, supply needs to be 19... so its like X and Y, only you can change both axels. Linear curve there some picture attached Attachment air temperature.jpg (228 Downloads)
Jerid Posts: 3 Rating: (0)
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10/14/2017 9:20 PM	Rate (0)
ixo65 Grandmaster Joined: 12/18/2014 Last visit: 9/16/2025 Posts: 35964 Rating: (4502)	What you want is 3-point step-control. If you want to control a 2-way valve, you need 2 digital signals: Set value greater than the actual value, then close (or open). Set value smaller than the actual value, then open (or close). Setpoint equal to actual value, then do nothing. PI controllers only pass an analog value to an analog output.

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10/14/2017 11:21 PM	Rate (0)
Diniz_ Bronze Member Joined: 7/2/2016 Last visit: 7/6/2025 Posts: 120 Rating: (29)	Jerid, i dont know it is the better way, but works. please evaluate if works for you. i hope this help... if was helpful please rate this post, thanks! Attachment 3 - RATIO LOGO!.zip (261 Downloads)
	hope this help, if it was helpful please rate the post! ---- BR, Diniz Carvalho
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10/15/2017 6:55 AM	Rate (1)
ixo65 Grandmaster Joined: 12/18/2014 Last visit: 9/16/2025 Posts: 35964 Rating: (4502)	Here is an example for the calculation of the setpoint for the temperature of the supply air duct. Attachment Setpoint_calculation.zip (272 Downloads)
	Last edited by: ixo65 at: 10/15/2017 6:56:31 AM attachment
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This contribution was helpful to 1 thankful Users Diniz_

10/15/2017 9:10 AM	Rate (0)
Diniz_ Bronze Member Joined: 7/2/2016 Last visit: 7/6/2025 Posts: 120 Rating: (29)	i think we have two good solutions for two different applications 1 for generates a remote setpoint to a PID controller (PI = for logo!) with a proportional valve, and another to control on/off valve(s), the point is how is your field actuator?
	Last edited by: Diniz [7] at: 10/15/2017 9:11:07 AM hope this help, if it was helpful please rate the post! ---- BR, Diniz Carvalho
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