TC M Temperature Controller User Manual V1.08
Electron Dynamics Ltd page
5
4 LED Status
The TCM series temperature controller has two LEDs that show the status of the controller.
TEMP OK ( LED 1) ON – Temperature ok in relation to set point and user defined settings
TEMP OK (LED 1) OFF – Temperature out of range
TEMP ALARM (LED 2) ON – Indicates an alarm or inhibit (External or Internal )
TEMP ALARM (LED 2) OFF – Temperature controller working correctly
5 Thermal Issues
5.1 Sensor Selection
The TCM series of temperature has many options for different sensor types. Each sensor type has
different characteristics which will affect your choice -
Sensor type Accuraccy Resolution Range
PT100 RTD <0.1 deg <0.005 deg -260 to +850 deg C
LM35,LM50 etc <2 deg < 0.005 deg -40 to 100 deg C
There are variations in size with some types so choose a suitable size for your application.
5.2 Thermal Assembly
This is a critical component in the system design, typically there are 2 problems –
-
the heatsink is not large enough
-
the thermal conduction between components is poor
It is worth reading the extensive material available from the peltier / TEC manufacturers to find out
the requirements for this.
See www.marlow.com and www.lairdtech.com
5.2.1 Heat sink size
The size of this should be chosen using the manufacturers calculations, it will need to be large
enough to radiate the heat required, typically they have a large heat capacity but often are more
limited in there capability to dissipate the heat. This is often seen when operating under
temperature control there is a continuous rise in heatsink temperature or rise in drive current. It
should be noted that there is a point in where the system can go into thermal runaway, as the
heatsink is unable to dissipate the heat properly and the temperature of the sample and heatsink
will continuously climb.
So this should be chosen to be larger than necessary.
Also using a fan on the heatsink can improve the thermal resistance to air by as much as 3 times
so this will give a significant improvement.
5.3 Thermal Conduction
It is important to ensure that there is a good thermal path between the Sample, TEC and heatsink.
Not only does this provide good heat removal / dissipation but will improve the temperature
stability.
Also important is that the mating surfaces are reasonably flat and that just enough heatsink
To Next Page