Other Information 9-5
9.4 Recommended Setup for MVAR Channels
(Using 4ma-12ma-20ma Transducer)
To Complete the Recommended Setup for MVAR Channels
1. Calculate the CT/PT value.
For example, suppose the resistor used with the transducer is 143 ohms and the transducer full
scale is - 400MVAR @ 4ma and +400MVAR @ 20ma. In this case, the calculation would be as
follows:
4ma (143 ohms) = 0.572V, which needs to equal -400MVAR
12ma (143 ohms) = 1.716V, which needs to equal 0 MVAR
20ma (143 ohms) = 2.860V, which needs to equal +400MVAR
2.860V – 1.716V = 1.144V as does 1.716V-0.572V=1.144V
400MVAR/1.144V = 349.650 which is the CT/PT that needs to be used in order to display
proper primary values.
2. In the Point Assignment Record for this analog channel, enter q(MVar) for the Channel Type,
enter 349.650 for the CT/PT value, and enter 5 for the Full Scale value (on the secondary
1V=1MVAR.) Click Save on the Point Assignment window.
3. In the APP Recorder, open the OScope (File menu, Show OScope). View the analog channel that
has been set up for MVAR.
4. With no signals attached to this MVAR channel un-calibrate the offset and the slope.
5. Apply a 1.716VDC signal (representing 12ma, 0MW) and calibrate the offset.
6. Apply a 0.572VDC signal and you should read a primary value of -400MVAR in the offset meter
box. The RMS meter box will read 400MVAR (no negative on RMS).
7. Apply a 2.86VDC signal. You should read a primary value of +400MVAR in the offset meter box.
The RMS meter box will read 400MVAR.
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