Armfield Instruction Manual
126
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.
Check that the temperature reading T1 is a sensible value (usually between 5 and 30
degrees Celsius depending on mains water temperature).
Select ‘Configure’ from the Sample menu, and set sampling to Automatic at intervals
of 30 seconds, with duration as Continuous.
The heating element is switched on and off manually using the switch on the
software screen. Switch on the heater, and observe the temperature T1. Check that
this rises as the heater operates. Switch off the heater again.
Heating Characteristics in Continuous Operation
The temperature in the vessel may be manually controlled by switching the power to
the heating element off and on. By switching the heater on and off using the switch
on the software screen raise the temperature of the water in the vessel to 30°C and
maintain this temperature by powering the heater off and on. Note the control actions
required to maintain a constant temperature within the water flowing through the
vessel. Record any differences between the time required for the water to rise and
fall in temperature. Note any time lag between applying a control action and
observing its effect.
(Note: if the mains water temperature is very high- approaching or exceeding 30°C-
then 40°C may be used as a Set Point value instead).
Select the
icon to begin data logging.
Maintain the temperature in the vessel, using manual control, for five minutes.
Select the
icon to finish data logging.
Create a new results sheet by selecting the
icon.
Disturbances
Within the software it is possible to introduce disturbances in the temperature inside
the process vessel by changing the flowrate of water through the vessel:
Select the
icon to begin data logging.
In the software, increase the PSV setting by 20%. Open the drain valve at the base
of the process vessel enough to balance the flow in and out of the vessel, so that the
fluid level in the vessel remains constant.
Note the control action required to maintain the temperature within the vessel at the
new flow rate.
Increase the PSV setting by a further 20%, and open the drain valve more to
maintain the fluid level within the vessel.
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