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Cascade Controller On Two Temperature Transmitters


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#1 A.Kangaris

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Posted 18 September 2020 - 02:08 AM

Hi,

 

Does it make sense to use a cascade controller on two temperature transmitters? One on the inlet and one on the outlet of an electrical heater?

I have a loop system, a buffer and an electrical heater. Fluid flows from buffer to an electrical heater which is heated up and return to the same buffer.


Edited by A.Kangaris, 18 September 2020 - 02:16 AM.


#2 breizh

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Posted 18 September 2020 - 03:53 AM

Hi ,

Keep it simple   !  T out should be controlled vs heat delivered by electrical heater . 

Later , if necessary you can consider to improve your control loops .

My view 

Breizh 



#3 sgkim

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Posted 18 September 2020 - 08:34 AM

Hi, Kangaris,

 

Typical cascade control loop has two controllers - one master controller and the other slave controller.  The master controller automatically inform the set point of the slave controller.   

 

For the electric heater circulating system, heater inlet temperature is assumed to be the same as that of buffer tank,  and the heater outlet temperature as the heater .    A master inlet temperature controller with a slave outlet temperature controller could make a cascade control loop.   The inlet controller shall set the set point of the outlet controller, which control the power to the electric heating elements.   

 

But be sure to protect the electric heater elements,  since the electric heater often overheat itself.  Heater skin temperature(s) should be monitored and input power be cut-off if it exceed a limited value.

 

An "overide" protection loop for the heater controller may often be recommended which can automatically shifted (selected) to the proper  output signal after comparing various controller output signals.     Heater vendors may help for providing your system configuration.

 

 

~Stefano Kim, 200918



#4 A.Kangaris

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Posted 28 September 2020 - 10:17 AM

Hi, Kangaris,

 

Typical cascade control loop has two controllers - one master controller and the other slave controller.  The master controller automatically inform the set point of the slave controller.   

 

For the electric heater circulating system, heater inlet temperature is assumed to be the same as that of buffer tank,  and the heater outlet temperature as the heater .    A master inlet temperature controller with a slave outlet temperature controller could make a cascade control loop.   The inlet controller shall set the set point of the outlet controller, which control the power to the electric heating elements.   

 

But be sure to protect the electric heater elements,  since the electric heater often overheat itself.  Heater skin temperature(s) should be monitored and input power be cut-off if it exceed a limited value.

 

An "overide" protection loop for the heater controller may often be recommended which can automatically shifted (selected) to the proper  output signal after comparing various controller output signals.     Heater vendors may help for providing your system configuration.

 

 

~Stefano Kim, 200918

 

Thanks Stefano,

 

Does the master controller change the SP of the slave controller? Because this is not what I want. SP of the outlet temp from the buffer needs to fixed and the inlet temperature will keep rising since buffer temperature will keep increasing. 






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