A PID controller is used to control the temperature of a jacketed batch reactor by adjusting the flow rate of coolant to the jacket. The temperature controller has been tuned to provide satisfactory control at the nominal operating conditions. Would you anticipate that the temperature controller may have to be retuned for any of the following instrumentation changes? Justify your answers.
(a) The span of the temperature transmitter is reduced from 30 to 15°C.
(b) The zero of the temperature transmitter is increased from 50 to 60 °C.
(c) The control valve “trim” is changed from linear to equal percentage.
(d) The temperature of the coolant leaving the jacket is used as the controlled variable instead of the temperature in the reactor.