Martel Electronics 135 - Manual (Page 53)

Use of Transmitter Simulator
Without Separate Power Source
The Model 130/135 Calibrator can be used to calibrate 2 wire, 4 to 20
mA transmitters without the need to use a separate DC power supply.
This is useful for bench calibration during construction check-out prior
to startup. Of course, if the loop is complete and energized, you would
not use this technique but would calibrate as usual.
Figure 2 shows the proper hookup. Note that this arrangement will not
work if the transmitter is connected in a complete 4 to 20 mA loop with
the customary 250 ohm dropping resistor. Be careful when making the
connection at the transmitter, if you short the leads, the calibrator mA
output fuse might blow.
The best technique is to connect the transmitter leads first, then
connect the calibrator. You must observe polarity or the transmitter
will not work.
Select Input mA and read the transmitter output on the display. The
Output mode of the calibrator may be set to any desired mode without
affecting the loop power. Milliamps may not be output at the same
time since this would over-load the internal power supply.
Figure 2
Application Notes 130/135 49
2 Wire
Transmitter
+ -