Armfield Instruction Manual
166
Disturbances
It is possible to introduce a disturbance by changing the flow rate through the coil:
Select the
icon to begin data logging.
In the software, select the Pump Control and change the Set Point value to 100%.
Select Apply and close the controller window.
Open the Heater Control again.
Maintain the temperature at the exit of the coil at 30°C (or the chosen Set Point) as
the increased process fluid flow rate. Note the control actions required to maintain
the temperature.
Select the
icon to finish data logging.
Create a new results sheet by selecting the
icon.
Holding Tube
The system may be modified by the addition of a holding tube after the process fluid
exits the coil. A suitable tube has been provided with the PCT40 base unit.
In the Pump Control, set the Mode of Operation to Manual and the Manual Output to
0%.
In the Heater Control, set the Mode of Operation to Manual and the Manual Output to
0%.
Disconnect the flexible drain tube from the exit to the coil, and connect the holding
tube. Connect the other end of the holding tube to the fitting for temperature sensor
T4, situated behind the large process vessel.
Repeat the investigations of process fluid flow rate and water bath temperature
described earlier in this exercise, but this time controlling the exit temperature for the
holding tube, T4. The pump controller should be reset to use T4 as the process
variable instead of T3 (select T3 from the drop-down selection box). Remember to
create a new results sheet for each set of results.
If laboratory time permits then the investigations of disturbances may also be
repeated.
Results
For easy identification or results, it is suggested that each results sheet is renamed
with a descriptive title (e.g. ‘Disturbances’, etc.). The entire workbook should be
saved with a suitable filename for future reference (e.g. PCT40 Exercise Z).
Each set of data should be plotted on a graph of temperature T3 against time
(without the holding tube) or T4 against time (with the holding tube).
Write up your experiment, commenting on the heating and cooling characteristics of
a continuous indirect heating process and the actions required for manual control of
the process. Give examples of situations in which indirect heating would be more
suitable than direct heating, and contrast the characteristics of this heating method
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