MP3009X TCM 4355X TRICONEX DCS Control System

The MP3009X TCM 4355X does not need to include the transmitter, as the calibrator replaces it. Note how the calibrator here acts as an active source of current instead of the passive load in the previous example. It not only provides information (i.e., regulates the current), but it also provides the energy in the circuit. The DC supply in the controller is not used for loop power because the “source” mode calibrator provides the necessary power to drive the current through the 250 ohm resistor. A very common use of the loop calibrator in “source” mode is to test a control valve for proper calibration, fast response, and to measure friction.

The circuit configuration of the MP3009X TCM 4355X is very useful to any instrumentation technician testing the response of a control valve, as it allows the signal to be finely tuned in the direct presence of the valve to monitor its motion. For example, if a control valve is suspected of having excessive friction in its moving parts, the technician can test the valve by increasing and decreasing the source current of the cyclic calibrator in small incremental steps. Large changes in current will cause the valve to overcome friction and move, but when friction exceeds the incremental force created by changing pressure, small changes will prevent the valve mechanism from moving.

The MP3009X TCM 4355X will connect to a device on the control valve called a positioner, which is a more complex device than an I/P sensor. In addition to converting the 4-20MA signal to air pressure, the positioner actively monitors the position of the valve stem to ensure it is in the correct position for any given 4-20MA command signal. Here, the technician uses a loop calibrator to verify that the control valve faithfully obeys the command signal across the entire 4-20 mA signal range. Another way to send a known current signal to an indicating instrument that provides loop power is to set up the loop calibrator so that it can simulate (or emulate) the behaviour of a Lobo-powered (2-wire) transmitter.

The analogue transmit mode of the MP3009X TCM 4355X is particularly useful for testing the transmitter cables and controller inputs to ensure that any 4-20MA signals sent by the transmitter are correctly received and displayed by the controller. This test is usually performed on a newly installed control system as part of the commissioning procedure, before the control process is initiated, in order to verify that the controller’s process variable inputs, 24 VDC power supply, and transmitter cabling are functioning correctly. A typical instrumentation technician will simulate several different current values (e.g., 4MA, 8MA, 12MA, 16MA, 20MA) with the calibrator in “analogue” mode while others monitor the controller’s PV displays and alarms to check proper functioning.