Exercise AA
169
Procedure
SAFETY NOTE: During this exercise the apparatus may reach temperatures hot
enough to cause burns or scalds. Do not touch the process vessel during the
exercise, or remove the coil or sensors from within the vessel. Allow the apparatus to
cool before draining the water or disconnecting any of the tubes from the process
vessel.
Select ‘Configure...’ from the Sample menu. Set data logging to Automatic at 30
second intervals with Continuous duration.
Open valve SOL 1.
In the software, select the Pump Control button for the gear pump controller. Enter a
Set Point value for the temperature of 30 degrees centigrade for water exiting the coil
(measured by T3). If the temperature of the local mains water supply is close to 30
°C then a higher set point value may be used instead. A value of at least 10 °C
higher than the mains water temperature is recommended.
Set the PID values for the controller. Suggested values are 100% for Proportional
Band, 0s for Integral Time Constant and 0s for Derivative Time Constant.
Set the Mode of Operation to Automatic. Apply the setting and close the controller
window. The gear pump should begin to operate.
Select the Heater Control button situated beneath the small process vessel on the
software screen.
Enter a Set Point value for the temperature of 50 degrees centigrade for water exiting
the coil (measured by T3). A value of at least 20°C higher than the process fluid
temperature Set Point (T3, set in the pump controller) is recommended, so the Set
Point should be modified if the local mains water temperature is close to 30°C.
Set the values for the controller in the appropriate boxes in the software. Set the
Proportional Band to 0%, Integral Time Constant to 0s and Differential Time Constant
to 0s. This configures the controller as an On/Off controller with a fixed hysteresis of
0.5% of full range.
Set a Cycle Time of 60 seconds, and Mode of Operation to Automatic. The controller
is now configured for Time Proportional Control of the heater.
Select the
icon to begin data logging.
Log the sensor outputs as the temperature in the process vessel reaches the Set
Point and stabilises. Continue logging for a further 5 minutes (or until the temperature
T3 stabilises), then select the
icon to stop logging.
In the software, select the
icon to create a new results sheet.
Temperature Set Point for Water Bath
Investigate the effect of changing the set point temperature of the heater controller:
Create a new results sheet by selecting the
icon.
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