Martel Electronics 235 - Manual (Page 74)

Calibrating Loop Powered Differential Pressure
Transmitter
Figure 9 shows a typical connection for calibrating a loop powered
differential pressure transmitter with a Model 230/235. In this
configuration, you would measure milliamps and pressure
simultaneously by pressing OPT with the calibrator in the output mode.
A suitable power supply can be constructed from two 9 volt batteries in
series.
Figure 9
Application Notes
230/235 69
Pressure
Module
+ -
Vent to
Atmosphere
Hand Pump
DP
Transmitter
HI LO
Loop Power Supply
15-24 VDC