Exercise O
117
On the software screen, set the PSV to 100% to allow cold water to flow through the
coil in the vessel, cooling the process fluid.
Observe the temperature T1. When the temperature has dropped to around 20 –
30°C, set the PSV back to 0%.
Create a new results sheet by selecting the
icon in the tool bar of the software.
Controller-controlled time proportioning
In the PCT40 software, select ‘Control’ to open the PID controller window.
Type in the Set Point value at which the on/off controller will operate. A
recommended starting value is 40°C for level.
Set P to 100%.
Leave I and D set to 0.
The Manual Control setting may be ignored.
Leave the Cycle Time at 10s.
Select the Automatic Control radio button and click on ‘Apply’. The valve should
begin to operate intermittently as the time proportional controller sends signals to
control it.
Select the
icon to begin data logging, and observe the temperature T1. Note the
behaviour of the heater as the temperature approaches the Set Point. When the
oscillations around the Set Point have settled, select the
icon to finish data
logging.
Disturbances
Within the software it is possible to introduce disturbances in the temperature inside
the process vessel by passing cold water through the coil inside the vessel:
Create a new results sheet by selecting the
icon in the tool bar of the software.
Select the
icon to begin data logging.
Log for two minutes (with the software taking readings every 30 seconds), then set
the PSV to 50%.
Continue logging for 15 minutes, then set the PSV to 100%.
Continue logging for a further 15 minutes, then set the PSV to 0%.
Log for a final 15 minutes, then select the
icon to finish data logging.
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