Carbolite PTC 12/20/150 - Manual (Page 5)

PTC
MF11 – 3.08 5
diameter is 7.5mm - larger diameters may experience too much heat conduction and give an
incorrect calibration.
Insert the thermocouple and end plug and support the cold end to ensure that the assembly lines up
with the axis of the furnace tube.
Switch on the instrument switch and set the desired temperature on the controller. Allow the unit
to warm up and stabilise. The reference temperature may be slightly lower than the control
temperature so adjustment can be made to the control setting to bring the reference temperature to
the exact temperature if desired; allow it to stabilise.
Either the output of the thermocouple or an indicated temperature can be checked against the
reference temperature and any error noted. This error can now be used to correct any readings
taken by the thermocouple. The noted error is the calibration of the thermocouple. Remember to
include the reference thermocouple error in calculating the calibration - see the reference
thermocouple certificate.
The calibration should be made at temperatures at which the thermocouple is to be used. If it is to
be used over a range of temperatures then calibrate it at a number of points over the range (for
example at every 100°), and plot a graph of error against temperature. A curve drawn through the
points can then be used to find the error at any temperature.