Section 4:
Application Notes
Supplemental application notes on the following topics are available by contacting J-KEM.
Application
Note
Subject
AN1
How to heat oil baths with your controller. (Included in Appendix)
AN2
Changing the controller’s thermocouple type.
AN3
Changing the heating outlet into a cooling outlet.
AN4
Using the controller for unattended fractional distillations.
AN5
Using the controller with inductive (motors, valves) loads.
4.1
Theory of How the Controller Works – Simply.
For the purpose of explaining how the controller
works, the example of a solution heated with a heating mantle is used. The principles are the same for all
heater types.
Power
ON
J -K EM
Scie ntific
Instruments for Science
M od el 210
120 Vac, 840 watts
120 vac
Power to heater
Thermocouple
Heating mantle
Temperature of process
from the thermocouple
Output
Power Level
1-10 ml
10-100 ml
50-500 ml
300 ml-2 L
> 2 L
Heat
Off
8 0. 0
o
C
*
Figure 2
The controller, the heating mantle and the thermocouple form a closed loop feedback system. If
the process temperature is below the set point, the controller turns the heating mantle on and then
monitors the temperature rise of the solution. If a small rise results (indicating a large volume is being
heated) the controller sets internal parameters appropriate for heating large volumes. If a large rise in
temperature results, the controller responds by loading a set of parameters appropriate for heating small
volumes. For the controller to work ideally, information needs to travel instantaneously around the
feedback loop. That means that any power the controller applies to the heating mantle must reflect itself
in an instantaneous temperature rise of the solution and the thermocouple. Unfortunately, this type of
instantaneous heat transfer from the heating mantle to the solution to the thermocouple just doesn't occur.
The delay time between when power is applied to the heating mantle and when the solution rises in
temperature; and also the converse, when power is removed from the heating mantle and the solution
temperature stops rising is the source of most controller errors. The reason for this can be seen in a
simple example.
Imagine heating a gallon of water to 80
o
C in a 5 quart pan on an electric range. Placing the pan
on the range and turning the heat to ‘high’ you’d observe a delay in heating while the range coil warmed-
up. This delay might be a little annoying, but it's really no problem. The real problem comes as the water
temperature approaches 80
o
C. If you turned the range off just as the water reached 80
o
C the temperature
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