3
Next, we must increase the positioner supply pressure to 100 psi, verifying that the pressure in the regulator pressure
gauge does not vary significantly (below 3 psi). After confirmation, simply lock the lock nut to fix the screw position,
without changing the regulated pressure. Finally, we remove the calibration device and replace the cap screw..
3 COIL CALIBRATION
For the positioner coil calibration, we must use the coil control parameter (CWR), read with a HART configurator such
as the DTM, for example. As a reference, the CWR parameter will indicate 100% when the coil has maximum electrical
current (1.6 mA) and 0% when it has minimum current (0 mA). Therefore, in the positioner control (PV = SP), the ideal
is that the CWR value is close to 50% (current at 0.8 mA).
In a similar way to the pressure regulator calibration, we must remove the
calibration cap screw from the coil, on the right – Figure 2.1. Then, simply
insert the gauge calibration device and apply supply pressure to the
positioner between 40 and 100 psi.
With the positioner turned off (no power supply), we must adjust the
pressure on the device's gauge between 3 and 4 psi. To do this, just
loosen the coil lock nut and adjust the screw with the help of an allen
wrench.
Figure 3.1 – VVP10 magnetic coil location.
Figure 3.2 – Coil current adjustment using DTM.
To manually vary the current in the coil using the positioner DTM, access the Maintenance and Coil Control menu –
see Figure 3.2.
To generate manual control of coil current, we must disable PID control. Next, when generating 0% on the CWR, we
must verify that the pilot pressure generated is between 3 and 4 psi. Next, generate 100% on the CWR (1.6 mA) and
confirm that the pressure generated is greater than 12 psi. Note in Figure 3.3 that the pilot pressure is below 10 psi
with the coil generating 100% on the CWR, requiring adjustment.
Figure 3.3 – Pilot pressures for CWR 0% and 100%, respectively.
