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Cooling - Heating - 1 probe

11/11/2008 4:46 PM	Rate (0)
inoxgan Posts: 20 Rating: (2)	I have to set up a cooling / heating on/off control with 1 pt100 and 2 thresholds. For cooling is very easy solution in the enclosed sample. when temperature rises OVER "on" threshold Q3 is set and cooling start until the temperature reaches "off" threshold. Now i am not able to setp up a circuit for heating. when the temperaturegoes below the "on" threshold Q4 is set (and the heater start) until the temperature reaches the "off" threshold. Thanks in advance for anyone who could suggest me any solution. But remember for customer "easy of use" i would like to set the "on" and "off" parameters exactly as i described and not to swap them and use off instead on and a "not" after. Thanks. again Attachment coolheat.zip (570 Downloads)
inoxgan Posts: 20 Rating: (2)
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11/12/2008 8:05 AM	Rate (0)
Solver Posts: 16 Rating: (0)	Hello Inoxgan! Here´s my proposal for the solution. I can´t see what was the difficult part, or have i misunderstod something. Reading the manual or help helps a lot. In this example I have changed the block parameters to sensor PT100. Regards Solver Attachment cooling_heating_v2.zip (598 Downloads)
Solver Posts: 16 Rating: (0)
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11/12/2008 1:18 PM	Rate (0)
inoxgan Posts: 20 Rating: (2)	Thank you Solver, but this is not the good solution for me. Probably i didn't explain myself correctly. Let me write an example so we may focus better the problem. now TempMax has "on" = 26 C and "off" = 25 At any time if the temperature of the pt100 rises over 26 the cooling is set until the temperature falls down to 25. To start cooling again i have to wait until the temperature rises again over 26 C. That's correct because i need a cooling system where i can set an "hysteresis", now TempMin has for example "on" = 10 "off" = 12 (note now off>on) At any time if the temperature is below 10 i have to start the heating until the temperature reach 12. Then i have to wait until the temperature falls again below 10 to start the heater again. So i have am heater with "hysteresis". In your example if the starting temperature is 8the heater will not start. I could set the "on" = 0. but doing so everytime the temperature is over the "off" the heater stop and as soon as the temperature is lower than off the heater is on. I have no "hysteresis". - Thanks for any help!
inoxgan Posts: 20 Rating: (2)
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11/13/2008 7:30 PM	Rate (0)
rosa Posts: 191 Rating: (58)	Hi!! try adding a not at the output of the Heating comparator block.. hope this helps Attachment temp.zip (601 Downloads)
rosa Posts: 191 Rating: (58)
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11/14/2008 12:36 AM	Rate (0)
Solver Posts: 16 Rating: (0)	Hello Inoxgan! If I have understod correct this time, Rosa suggested the solution You did not want, even if it is a working solution. Another way to solve this problem is to add a on-delay block betveen the analog treshold trigger and the output. This way You can create a hysteresis to the treshold. Set the on delay time depending on Your process and Your heating system, so that You get proper switching rate and temperature fluctuation. Normally it is not advisable to add extra dead time to control systems, but maybe it is acceptable in this case. Maybe later on we can figure out another, better, solution to Your problem. Best regards Solver Attachment cooling_heating_v3.zip (615 Downloads)
Solver Posts: 16 Rating: (0)
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