ThSwitch on the SL1 Mainframe and then if necessary, adjust the Thermocouple
Amplifier as follows:-
Connect the output (red) socket of the SL114 to the SL1 meter input. Switch
the SL114 selector switch to 'SET ZERO' and adjust the SL1 'SET ZERO'
control until the meter indicates zero. Switch the SL114 selector switch to 'INT
CJ'. (If an external measurement system, for example a chart recorder, is also
connected to the SL114, then zero the external system also.)
Temperature Sensing is preferably carried out with the SL114 Thermocouple
Amplifier. Alternatively, the output of the thermocouple may be monitored
using the SL103 Differential Amplifier. Note that the SL114 will give a
reading temperature in degrees centigrade directly while the SL103 will result
in an output of 400pV per degree above ambient.
A chart recorder may be used to enhance the value of this experiment by
providing hard copy of results. The recorder should be connected in parallel
with the SL1 meter. Suitable control settings are 2mm/min and 5mV/cm.
Set up the equipment as shown in the diagram and switch on the SL1 and
SL20.
Turn the control of the thermostat clockwise to the 30°C mark. The lamps will
come on and the temperature will rise. Record the temperatures of switch on
and switch off after the system has passed through at least three cycles.
Rotate the thermostat controller to approximately 35°C and again record the
switching temperatures. Repeat this procedure in increments of
approximately 5°C until the thermostat controller is set to 60°C, or no further
increase in temperature is observed. Plot a graph of control position against
temperature.
When the capillary bulb contacts are closed, the heating lamp system is
completed via the power switching relay. As the heating lamps heat up the
controller, the contacts will eventually open and switch off the heating system.
On cooling down the contacts will remake to re-establish the heating cycle.
Note the temperature at which the contacts open and the temperature at
which they reclose. Compare the response and hysteresis of this switching
system with the bimetallic strip systems used earlier. Note that switching
points and heating and cooling rates will depend on ambient temperature and
ventilation effects.