 In this module, we will talk about the automatic control system of pH. As we discussed in our previous module that what kind of the neutralizing agent, mean acid solution or alkali solution. What kind of they should be and what kind of their concentration should be. We cannot use the diluted, we cannot use a highly concentrated material. So, there is a limitation. So, if we have a choice and then how we have to control, automatic control system. So, in this case that pH control system consists of a pH probe and this pH probe is very sensitive to temperature because we have to use such pH probes which can withstand the sterilization temperature mean 121 degree Celsius. So, the normally when you use in a laboratory pH probes and a pH meter that cannot withstand to that high temperature. So, the pH probe used in a fermenter vessels that having a special material. Then is the alkali delivery system and then is the acid delivery system. So, the pH probe sense the actual pH inside the fermenter and then that signal to either pump 1 or pump 2, pump 1 attached with the alkali and the pump 2 can attach with the acid. So, alkali delivery system and acid delivery system. So, in this you can see that on the left side here there is the alkali and on this side is the acid and here you can see that is the pH controller and this one is a pH probe. So, this sense this pH so according to the change in pH if the pH decrease 7 to world 6, 5 and so on then that signal to the alkali but if the pH go or increase from 7 to 8 and then and then that having the signal to the acid delivery system. So, how this total delivery system can be managed. So, if we see an example for the pH control indeed all other fermenter control system designed to have a dead band. Sometime it happen if we want to set the pH at 7 and the pH goes 7.1 or the pH goes down 6.9 what happen then there will be on and off actually. So, if there is a one drop of alkali or a one drop of acid that can change 7.2 or a 6.8. So, there is a continuously on and off of the alkali and the acid delivery system. In result of that in such case when there is a continuous on and off system then that can effect the fermentation volume. So, one is a set point that what is the pH we require that is known as the set point and the upper limit that is known as the upper band and then is the lower limit. So, how we can place the upper band and the lower band in later slide you can see that how we can decide the upper band and the lower band with respect to the set point. The set point actually the pH which the fermenter is being attempt to be controlled. In this example if the fermentation is to be run at 6.5 pH then the set point is 6.5 and we want to set the 5% dead band. Dead band mean in which there will be no pump either acid or alkali will be on and off. So, that 5% is our dead band. So, by calculating that if there is a 5% just if you say 5% that is 105 divided by 100 mean 1.05. So, multiply by the set point and then the answer is 6.83 on the same way when there is a 5% minus then is a 95 so 95 or 100 that is mean 0.95. So, when you multiply this 0.95 with 6.5 the answer is 6.18. So, as concern the upper band and the lower band so 6.83 pH will be the upper band and 6.18 will be the lower band. So, if there is a set point of 6.5 and if the pH will go 6.7 then there will be a no pump on and off the same case if the pH will go 6.09 then there will be a no pump on. So, if that touch to 6.83 then there will be the on of acid pump and if this pH will touch to 6.18 then there will be the signal to that alkali pump. So, this why the calculation of the upper band and the lower band but that directly depend upon the dead band which we decide before controlling or optimizing our processes. So, as many fermentation tend to produce the acids rather than the substances that increase the pH acid addition is often not required indeed not all fermentation need the continuous pH control but in some cases when there is the our product is directly association as there are the growth of the organism is directly affected by the pH change then the pH control system should be active.