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Appendix C. Determining an SVI Positioner
Compliance Voltage in a Control System
This discussion explains how to determine compliance voltage for an SVI positioner. It applies
to the SVI II AP, SVI II ESD, SVI II APN and SVi1000.
A definition of compliance voltage is: The voltage that must be available at the control system
output in order to drive the control current through the SVI II AP and all the resistive devices in
series with it.
Measuring the voltage across the SVI II AP terminals doesn’t give the true available system
compliance voltage as the positioner self-regulates voltage as current flows through it.
Additionally, it also doesn’t confirm what system voltage is available under load conditions.
Therefore, if compliance testing needs to be done, it is best done before installation.
Use a 1K potentiometer as this is the maximum for most analog output cards and as at 20 mA
this equals 20 VDC, which is a sufficient maximum.
Compliance Test Set-Up
1.
Configure a test set-up as in Figure 36.
Figure 36 - Compliance Voltage Test Set-Up
2.
Send 4 mA to the test set-up.
3. Increase the potentiometer value until the loop current reaches 3.95.
4. Read the voltage across the potentiometer, which should be > 11 VDC. This is the available
system voltage at the minimum output.
5.
Send 20 mA to the test set-up.
6. Increase the potentiometer value until the loop current reaches 19.95 mA.
7.
Read the voltage across the potentiometer, which should be > 9 VDC. This is the available
system voltage at the maximum output.
Table 6 lists some compliance voltage readings at positioner terminals at several currents.
