Martel Electronics 235 - Manual (Page 71)

mA/V Module
The module provides a powered 4-20 mA output signal for calibrating
the inputs to 4-20 mA controllers and indicators. This mode is used to
calibrate instruments that are not providing the loop power. Figure 6
shows the module connected to an instrument that is not providing
loop power.
Equipment configuration may require that a loop be calibrated with the
loop power supply energized. In this configuration, the calibrator’s
internal power supply would oppose the loop power supply and the
calibrator will not be able to generate the calibrating current.
The module can be connected to a powered loop with the calibrator’s
internal power supply aiding the external loop power supply as shown
in Figure 7. This connection method is a simple polarity reversal of the
standard powered milliamp configuration, sometimes called
transmitter simulate mode.
Application Notes
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