Temperature control

[Emach]

Hi ya'all, I have a SAE #2 test bench with a jerry rigged stand alone pump and heater that feeds heated automatic transmission fluid (ATF) into the test chamber. We also have a water based cooling loop that feeds through the metal housing of the test chamber but doesn’t directly interact with the ATF. The issue we are running into is maintaining a target ATF temperature of 150 degrees Fahrenheit throughout the test. Where maintaining that temperature gets difficult is when we apply the clutch we see upwards of 550 degrees Fahrenheit. We can manually, continuously run the cooling loop but it has a nasty habit of dropping the clutch’s temperature too low. Currently a Chromalox 2110 controls about 360W of heaters running at 120VAC. Does anyone know of a good temperature controller that will allow me to modulate the cooling loop flow at the same time as the heater? I am willing to install a proportioning valve on the cooling circuit. The machine tests for hundreds of hours at a time, so decreasing the time for the machine to return to the temperature setpoint after an engagement would be extremely beneficial. Regards, Emach As an aside, anyone want to buy two gently used SAE #2 machines?

[DanW]

The key term is heat/cool. Controllers that do heat/cool control, like a Honeywell UDC 2500 or 3200 have two outputs, one for heating, one for cooling. When running "duplex" mode (Honeywell's term for heat/cool) the controller is typically configured so that the heating band and the cooling band do not overlap. They also typically have two sets of PID constants, so that the heating loop can be tuned independently of the cooling loop. The Honeywells have a choice of PID (modulating control) or ON/OFF for either or both loops. I happen to prefer the Honeywells because the manual has 4 pages of instructions on running a duplex autotune under various conditions.

[Emach]

Thanks for the advice Dan. I looked at Chromalox's heat/cool offering and it appears to be a Cadillac model and runs $900! Are the Honeywells a little bit cheaper?

[Mickey]

Here's another option. I have used them before, no problems. http://www.miinet.com/products/data_sheets/545.pdf