Consider this control system, set up to maintain the temperature of a chemical reactor vessel at a constant "setpoint value." The reactor's source of heat is a steam jacket, where hot steam is admitted through a motor-operated (M) control valve (TV) according to the temperature inside the reactor sensed by the temperature transmitter (TT):
TIC
SP
T1
Reactor
M
Steam jacket
From steam supply (boiler)
To condensate return
You arrive at work one day to find the operator very upset. The last batch of product emptied from the reactor was out of spec, and the temperature displayed by the indicating controller (TIC) shows it to be 197°F. The setpoint is set at 175°F, and the controller is in the automatic mode as it should be.
Your first step is to look at the indication on the controller showing the output signal going to the motor-actuated steam valve TV. This output signal display (the "manipulated variable") shows 0%, which means "valve fully closed."
Next, you decide to check the temperature shown at the temperature indicator (TI) located near the temperature transmitter TT on the reactor. There, you see a temperature indication of 195°F.
From this information, determine what is the most likely source of the problem, and explain how you made that determination.
