Other Information 9-6
9.5 Recommended Setup for a Current Channel using a 4ma-
20ma Transducer (e.g. measuring generator field current)
To Complete the Recommended Setup
1. Calculate the needed shunt value.
For example, suppose the resistor used with the transducer is 270 ohms (measure with an accurate
meter) and the transducer full scale is 2000A @ 20ma. In this case, the calculation would be as
follows:
4ma (270 ohms) = 1.08V, which needs to equal 0 Amps
20ma (270 ohms) = 5.40V, which needs to equal 2000 Amps
5.40V – 1.08V = 4.32V
thus 4.32V/2000A = 2.16 milliohms which is the shunt value that needs to be used in order to
display proper values.
2. In the Point Assignment Record for this analog channel, enter C(Adc) for the Channel Type. Enter
1 for the CT/PT value, enter 2000 for the Full Scale value (ABS will automatically = 5000), and
enter 2.16 milliohms for the external shunt value. Click Save in the Point Assignment window.
3. In the APP Recorder program, open OScope (File menu, Show OScope). View the analog channel
that is being setup with this transducer.
4. With no signal attached to this transducer channel, un-calibrate the offset and the slope.
5. Apply a 1.08VDC signal (representing 4ma = 0 Amps) and calibrate the DCoffset.
6. Apply a 5.40VDC signal. You should read a value of 2000A for this transducer current channel.
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