a Resistor-Based Temperature
Example: Changing the Range of a 5CJ-020
Using a Multi-turn Potentiometer
Using a Potentiometer with Range Scaling Resistors
Using Higher Resistor Values for Setting Temperatuer Range
If one of our temperature controllers is set using
it generally uses a single turn potentiometer. (The on-board
of the 5C7-350 is one exception, and it uses a 25 turn potentiometer.
remote potentiometer of the related 5C7-350A is a single-turn
The potentiometer we provide generally covers a fixed temperature
You can improve the temperature settability anywhere within that range
by changing the potentiometer or adding to it.
Some of our computer compatible controllers also
have an input for an
optional 5KOhm single-turn potentiometer in order to manually adjust
set point temperature. The methods discussed below for changing the
range of the potentiometer apply to these controllers as well.
To make your calculations for an adjustment to the
circuit you will
need to know the appropriate temperature range. See the specifications
on our web site the controller you are using. Some controllers have
temperature ranges depending on the type of sensor used, for example,
5C7-461 has different ranges depending on the type of thermocouple you
use. Those ranges are specified on our web page for that controller.
The methods used to change the temperature range
of a potentiometer
are presented below in the form of a specific example.
EXAMPLE: THE RANGE OF A 5CJ-020
The Model 5CJ-020
uses a single turn 5 KOhm
potentiometer. It has the standard 270 degrees of turn from one end to
With the temperature range of 0°C to 750°C
this is a coarse
adjustment. Generally, an application for this low cost off-the-shelf
allows for such a coarse adjustment, but if you need improved
set point resolution you can use one of the following methods.
USING A MULTI-TURN POTENTIOMETER
One way to improve the adjustment resolution is to
simply replace the
single-turn potentiometer with a multi-turn potentiometer.
USING A POTENTIOMETER WITH RANGE SCALING RESISTORS
The temperature range in Fahrenheit is 32 F to
If you want a maximum temperature of 275 F we can
calculate a ratio
(275 max desired - 32) / (1382 max - 32) = 18%
5 KOhm max * 18% = 900 Ohms
So, a 1 KOhm single-turn potentiometer in series
with a 4 K Ohm fixed
resistor will come close to what we need by providing an adjustable
of 32 F to 302 F.
See the drawing below.
A 1 KOhm single turn potentiometer with 270 degrees of spin would
a temperature adjust resolution of about 1 degree Fahrenheit for each
of turn. Of course, a multi-turn 1 KOhm potentiometer would provide a
USING HIGHER RESISTOR VALUES FOR SETTING TEMPERATURE RANGE
Actually, the circuit can probably handle higher
resitances, and our
engineer would probably try using a 20 KOhm resistor with the 5 KOhm
(instead of the 4 KOhm resistance and 1 KOhm potentiometer that is in
drawing. If that works you can leave the 5 KOhm potentiometer where it
is and simply splice in the 20 KOhm fixed resistor in order to get the