31
Logix
®
420 Digital Positioner FCD LGENIM0106-07-AQ – 10/15
flowserve.com
14 TROUBLESHOOTING
14.1 Troubleshooting Guide
Table 15: Troubleshooting Guide
Failure
Probable Cause
Corrective action
No LED is blinking.
1. Current source too low.
2. Voltage of current source is too low.
3. Incorrect wiring polarity.
1. Verify current source supplies at least 3,8 mA.
2. Verify voltage source supplies at least 10VDC.
3. Check wiring for correct polarity.
Erratic communications. 1. Current source bandwidth not limited to 25Hz.
2. Maximum cable length or cable impedance exceeded.
3. HART modem connected to PC RS-232 port not receiving
enough power
4. Interference with I.S. barrier.
5. Current source stripping (filtering) HART signal.
1. Maximum allowable current source rate of change is 924 mA per
second.
2. Check cable size, length and capacitance. See Section 7
ELECTRICAL CONNECTIONS.
3. Verify laptop battery is not low.
4. Must use HART compatible I.S. barrier.
5. Use a 250Ω resistor and a 22 µF capacitor to create a HART filter
according to the following schematic.
22 F 250
Control System
HART
Comm
Device
To Logix
Unit does not respond to
analog commands.
1. The positioner is in digital command mode.
2. An error occurred during calibration.
1. Switch to analog command mode using the procedure outlined
in Section 8.3 COMMAND SOURCE RESET, use the ValveSight
DTM, or use a handheld communicator.
2. Check Status Codes. Correct calibration error. Recalibrate.
Valve position reading is
not what is expected.
1. Stem position sensor mounting is off 180 degrees.
2. Stroke not calibrated
3. Tight shutoff (MPC-Minimum position cutoff) is active.
4. Custom characterization or soft stops are active.
1. Reposition the sensor.
2. Perform a Stroke calibration (Quick-Cal).
3. Verify Tight Shutoff settings.
4. Verify custom characterization or soft-stop limits.
Position is driven fully
open or closed and
will not respond to
command.
1. Stroke is not calibrated.
2. Inner-loop hall sensor is not connected.
3. Wrong air action was entered in software.
4. Actuator tubing is backward.
5. Electro-pneumatic converter is malfunctioning.
6. Control parameter inner-loop offset is too high/low.
1. Perform stroke calibration (Quick-Cal)
2. Verify hardware connections.
3. Check ATO (Air-to-open) and ATC (Air-to-Close) settings.
Recalibrate using Quick-Cal to apply settings.
4. Verify ATO/ATC actuator tubing.
5. Replace electro-pneumatic converter.
6. Adjust inner-loop and see if proper control resumes.
Sticking or hunting
operation of the
positioner
1. Contamination of the electro-pneumatic converter.
2. Control tuning parameters not correct.
3. Packing friction is high.
1. Check air supply for proper filtering and meeting
ISA specifications ISA-7.0.01.
2. Lower proportional gain settings.
3. Enable the stability DIP switch on the local interface and
recalibrate. If problem persists, adjust pressure control window
with handheld communicator or ValveSight and recalibrate.
LCD backlight flickering
or dim.
1. The backlight uses any residual power not used by other func-
tions of the circuitry.
1. Fluctuations in the LCD backlight are normal. No action required.
