Grant Instruments RC - Manual (Page 10)

Recirculating Chiller
Part No 09931/Issue 8 Page 10 August 2001
3.3.1 Setting high alarm offset
After setting the required temperature, press the button until the display reads “1dHi”.
Press and release the or
↑ button to display the present value of the high alarm.
Press the
the or button again to set the new value for the high alarm.
Example: If the set temperature is 15°C and you want the high alarm
to operate if the temperature rises above 20°C , set the high
alarm offset to 5°C .
3.3.2 Setting low alarm offset
Press the button until the display reads “2dLo”. Press and release the or
button to display the present value of the low alarm. Press the or button again to set
the new value for the low alarm.
Example: If the set temperature is 15°C and you want the low alarm
to operate if the temperature falls below 5°C, set the low
alarm offset to 10°C.
3.4 Cooling
Switch on the cooler for cooling of external loads. Cooling can be controlled at 60°C or below.
However, if there is no external heat load, the RC cannot maintain an operating temperature of
above approximately 35°C with the cooler switched on.
Do not switch the cooler on if:
i) circulator has been tilted by more than 25° during the past six hours.
ii) if the cooler was switched off within the last 10 minutes.
3.5 Tuning
You will normally need to tune the controller only once, during the initial commissioning of the
process. However, if the process under control subsequently becomes unstable (because its
characteristics have changed), you can retune again at any time for the new conditions.
It is best to start tuning with the process at ambient temperature. This allows the tuner to
calculate more accurately the low cutback and high cutback values that restrict the amount of
overshoot or undershoot.
Press the button until the display reads ‘tunE', then press the or button to
select ‘on’. Press the button again to revert to the display of the actual temperature.
Self-tune is now in operation; the display will flash’tunE’ to indicate that tuning is in progress.
Set the setpoint to the value at which you will normally operate the process. The controller will
wait for one minute during which time you can change the setpoint. When the display stops
flashing ‘tunE’ tuning is complete.
3.6 Undertemperature thermostat
To protect the system from freezing when water is being used, switch the water/glycol switch to
water, a low temperature cutout will operate below + 10°C, switching the cooler off. The cooler
will switch on again when the water temperature has risen to approximately +15°C.
For operating temperatures below +10°C, we recommend that water/glycol is used and the switch
set to water/glycol.
It is possible to run the system using water at temperatures down to +5°C, with the water/glycol
switch set to water. Once the liquid temperature has reached +10°C, reduce the set temperature
in 1°C steps to +5°C.
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