Switch on 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 of temperature in degrees Celsius directly while the SL103 will result
in an output of 40pV per degree above ambient.
A chart recorder may be used to enhance the value of this experiment by
providing hard copies of results. the recorder should be connected in parallel
with the SL1 meter. Suitable control settings are lOmm/min and 5mV/cm.
Set up the equipment as shown in Figure 4.1. and switch in the SL1. Set the
control knob of the Low Voltage Power Supply to approximately 3 o'clock.
Allow the system to pass through 3 cycles to attain thermal equilibrium. At a
certain temperature the bimetallic controller will open and the light will
switch off. Thereafter the system will cool down until the bimetallic element
remakes its contact to switch on the heating lamps again.
Note the temperature as indicated on the meter when the bimetallic sensing
element opens and when it closes.
Note in particular, that the operating temperature is not very codtant and
that there is a large difference in temperature between the point at which the
strip operates and the point where it remakes contact.
Note that the switching points and heating and cooling rates will depend on
ambient temperature and ventilation effects.