Process Control

Topics: Control theory, Controller, Derivative Pages: 9 (2951 words) Published: December 11, 2012
PC: Process control

Process control is the basis for many solutions in the field of chemical engineering. It involves managing one or more system parameters. These parameters can be flow rate, pressure or temperature. The main aim of process control is to produce algorithms for input and output within a desirable range depending on the requirements of the specified process,

The microcontroller in this testing will be PCT40 process control apparatus software. The parameters being controlled will be the float switch, differential level switch and the pressure sensor. The float switch controls the on/off valve in this process and it controls the flow into the process vessel. The differential level is control measure for the water level. It uses the difference in conductance between air and water through two electrodes at different levels and an earth rod. This mechanism allows a switch to activate valves to turn off or on when the water level is at maximum or minimum respectively. The pressure sensor works by measuring the pressure in the vessel relative to atmospheric pressure. The aim is to produce a PID with minimal offset, oscillation or overshoot. The algorithms used to achieve this will be proportional, proportional + integral, proportional + derivative and proportional + integral + derivative (PID).

* PCT40 Process Control Apparatus software
* Level switch (Float switch)
* Lid
* Differential Level switch
* Process Vessel
* Level scale
* Level sensor

Hazard analysis
Basic PPE was worn throughout the experiment. There were no immediate hazards, as the fluid was water, at low temperature and pressure. The vessel was kept from overflowing and causing spillage by the differential level switch. The major hazard was the potential of water to leak on electrical components. Finally, other experiments happening in the lab were a latent hazard.

Procedure (Full Procedure in appendices)
1. Firstly, it was necessary for the familiarisation of the computer interface and learn about the possible algorithms. 2. Next, a run was done using the float switch with data logging set at five seconds. 3. The differential electrodes were then adjusted at 20 mm for the blue topped rod to start and 40mm for the red topped rod. 4. From a water level of 190mm a run was started of the differential level switch. 5. PID control was then controlled using a level sensor. Proportional control was measured individually first. The set point was at 200mm, with a cycle time of 10 seconds and proportional band of 10%. 6. Then runs were done at 5%, 2% and 1%.

7. The next algorithm was PID control using proportional and integral control. Step 5 was then repeated but a 2% proportional band was used with the integral time changed to 5 seconds, 20 seconds and 50 seconds. Derivative time was set at zero. 8. Proportional and derivative were the next variables to be tested. Step 5 was replicated and the proportional band was set to 2% and the derivative time was set at 1 second and 5 seconds. The integral time was set at 0. These runs were then observed and recorded. 9. Finally, self testing was applied using all three variable controls to try and achieve the optimum setting.

The first run was done using a float switch. This requires manual adjustment therefore there is no computer control algorithm. From graph 1,(all graphs mentioned will be in the appendix,) it can be seen the water level is maintained at the set point with little oscillation. It can be seen on the graph after 55 seconds the water level is sustained at 200mm. The differential switch also required manual adjustment. From graph 2 when there was a 20mm difference between the electrodes, the oscillations were large but very constant, when the difference between the electrodes was reduced, the oscillations were still quite large and the set point was not reached. The next was the...
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