Question concerning using the 'Cooling Difference' function

[Saldarya]

Hey all,

So my current settings for chiller control show a nominal temp of 78.62 and a Hysteresis value of .45 deg. This range was having my chiller turn on and off to often, so I choose to use this 'cooling difference' feature.

I set this value to .72 deg.

Based on what the manual says, this shoudl kick the chiller on at 79.34 degrees.

Problem is, it is now at 79.7 and still the chiller still is not on.

All settings were done in Celsius and then displayed in Farenhiet.

What am I missing here?

Thanks!

 

[Saldarya]

Thinking that I was making it difficult on myself, I set the cooling difference back to 0 and change the Hysterisis to .72 F. The Nominal remains 78.62. Now when the chiller turns on at 79.7, it turns off at 79.0, still not doing what I want.

So lets rephrase the question...

The nominal temp of 78.62 is fine, that is my target temp.

I want the controller to turn the chiller on at 79.5 and then turn off when it reaches the nominal temp of 78.6.

How do I set this up.

Thanks,

 

[AQD_ottawa]

set mthe hysterisis back to 0 also and then test.

 

[Saldarya]

Software will not met me set the Hysterisis lower than .15C.

Bobby

 

[AQD_ottawa]

sorry i emant to the minimum

 

[AQD_ottawa]

what temp do you have the thermostat of your chiller set to and the same question for your heater

 

[Saldarya]

Neither the Chiller or the Heater have their own thermostats. They are only controllable via a controller of some type.

Thanks for the help Michael!

 

[AQD_ottawa]

Because of the min value of hysterisis you will always have a slight varient this is to stop damaging switching to your chillers compressor.

Taking into account the .72F you are prety much within this range as expected.

 

[Matthias Gross]

Hi Bobby

if you want to reduce the switchings you only need to increase the hysteresis. For example to 1°C.
Set the nominal value as needed.

The cooling difference can be used if you want to heat AND cool your water and you want to have some degrees between where nothing happens.

 

[Saldarya]

Well, I set the Hys to .72F and the cooling to 0. The chiller comes on at 79.3 and turns off at 79.0. The nominal value is still set at 78.6. For whatever reason, the settings will not allow the chiller to get the temp back down to teh nominal temp.

I dont get it. no matter what I set things for, the variance in turning chiller on and off is .3-.4 degrees.

Again, is it possible to set this up so that it has a set point of say 78.5F, chiller turn on at say 79.25 (a .75 variance), and turn off when it reaches that set point of 78.5?

WHen I increase the Hysteresis, ti does change the temp at which the chiller turns on above the set point, but it does not get it back down to the nominal value.

Thanks for your help and patience guys, I am sure that there is something I am missing here, but it seems that it should be easy to say, "my set temp is X, and turn chiller on at Y until X is met."

Hope that makes sense.

Bobby

 

[Matthias Gross]

This behaviour is normal and described in the manual under 3.7.8

Since chiller, heater and substrate heater must work together it is necessary that the switching points of these devices are different. It must be avoided that chiller and heater work against each other.
That means that the temperature of the water will slightly be above the desired value if you only use a chiller, and it will be slighly below the desired value if you only use a heater.
If you use a chiller and you want to get exactly a specific temperature then decrease the nominal value.