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• garima singh

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VIRTUAL LAB EXPERIMENT

Experiment number: 1

Objective: To determine the control characteristics of pH controller (M7822N) of Bio-Engineering AG fermenter.

Theory: The adequate pH control action in the bioreactor is highly dependent on the several factors e.g., density, viscosity & volume of the fermentation broth, strength of acid and bases, on/off time of the pumps, pH zone (band) of control action etc. The Bio-Engineering AG, Switzerland fermenter has M7822N pH controller which allows to manipulate above parameters to arrive at optimal set point. Description of the pH Controller: The different components of the controller are described below: 1. pH/mv potentiometer – This potentiometer enables adjustment of the slope of pH electrode by means of a calibration buffer. 2. Asymmetry potentiometer – It is used to adjust the zero

mV point of the pH signal (pH 7.0). 3. Temperature potentiometer – A manual control to correct for temperature coefficient of pH electrode. 4. Set point potentiometer – It is used to set the mV or pH set point. 5. P-band potentiometer – It serves to adjust the width of the P-band amplification. A low P-band translates to strong amplification. 6. TON/TOFF Potentiometer – These two controls are primarily used to adjust the valve opening or closing time in relation to the mid-point of the P-band. Keeping both the potentiometer at the same value will ensure that opening and closing times of the corresponding values are equal in the centre of the P-band. Under this situation the transfer function of the system would be linear. These controls of the system adjust the controller to the shape of a titration curve so that even with a titration curve having steep end point the transfer behavior remains linear and control system does not begin to oscillate. The dead band of this P-controller will be characterized by a situation in which none of the two values is actuated and it represents 10 % of P-band.

Observation: The graphs obtained during the experiment

Graph no. 1

p-band=0.5, t-on=5, t-off=5.

Oscillation and offset both were observed. Did not reach the set point.

Graph no. 2

p-band= 0.5, t-on= 5, t-off=0.5

No oscillation observed. Offset can be seen, did not reach the set point. Long time to implement the control action. Graph no. 3

p-band= 1.0, t-on= 5, t-off= 5

Oscillation observed. Never reaches the set point

Graph no.4

p-band= 1.5, t-on= 0.5, t-off=5

No oscillation or offset observed. Better control action noted. Desired result obtained.

Graph no. 5

p-band= 1, t-on= 5, t-off= 5. pH calibration is done.

No oscillation observed. Takes a very long time to reach the set point.

Self-Evaluation

Name: kumari garima singh Msc microbiology 3rd semester 1911402029