In this process, two chemical streams are mixed together in a reactor vessel. The ensuing chemical reaction is exothermic (heat-producing) and must be cooled by a water cooling system to prevent overheating of the vessel and piping. A temperature transmitter (TT) senses the reaction product temperature and sends a 4-20 mA signal to a temperature indicating controller (TIC). The controller then sends a 4-20 mA control signal to the temperature valve (TV) to throttle cooling water flow:

reactor vessel

Suppose an instrument technician adds a temperature-indicating chart recorder (TIR) to the temperature transmitter circuit, necessitating the addition of a 250 ohm resistor to the 4-20 mA circuit to provide a 1-5 volt voltage signal which the recorder can read. Now the 4-20 mA temperature circuit has more resistance in it than it did before.

Describe in detail the effect this circuit modification will have on the performance of the cooling system.

Answer :

This circuit modification will have absolutely no effect on the performance of the system, as long as the loop-powered transmitter receives its minimum terminal voltage for proper operation.