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 Variable
Reluctance Pressure Transducer Troubleshooting Guide
This troubleshooting guide describes
the most common variable reluctance transducer symptoms, problems
and solutions.
Most performance problems associated
with variable reluctance sensors are the result of dirt in the
sensor cavity or improper torque on the body bolts. Dirt in the
sensor cavity can impede the movement of the sensing diaphragm.
The diaphragm moves only about two thousandths of an inch from
zero to full scale pressure. Any bit of sand or dirt can keep
the diaphragm from sensing the correct pressure. Often the output
a contaminated transducer will be linear up to a certain pressure,
but then the output stops changing. Simply disassemble the transducer
and clean the sensor cavities.
Body bolt torque is also important.
The DP15 transducer, for example, requires 115 inch-pounds of
torque on each of the four body bolts. Less torque means that
there is less clamping force on the diaphragm. This allows the
diaphragm to slip out from between the coil housings during full
scale pressure excursions. Excessive hysteresis and non-linearity
often result. The solution to this problem is easy; simply loosen
and then re-torque the bolts.
Problem: Zero
Balance Too High
Cause: Warped or Damaged
Diaphragm
Solution: Reverse diaphragm. If still out of spec replace
diaphragm.
Cause: Contaminated Pressure
Cavity
Solution: Clean & Reassemble
Cause: Body Bolts Improperly
Torqued
Solution: Loosen & Re-torque Bolts. See Torque Guidelines.
Problem: Full-Scale
Output Not in Specification
Cause: Diaphragm Incorrect
Solution: Check Diaphragm Range
Cause: Body Bolts Improperly
Torqued
Solution: Loosen & Re-torque Bolts. See Torque Guidelines.
Cause: Obstruction in Pressure
Cavity.
Solution: Disassemble & Clean. Clear ports.
Problem: Excessive
Non-Linearity
Cause: Over-ranged Diaphragm
Solution: Check Diaphragm Range. Replace if Necessary.
Cause: Obstruction of Diaphragm
Movement
Solution: Clean & Reassemble
Cause: Body Bolts Improperly
Torqued
Solution: Loosen & Re-torque Bolts. See Torque Guidelines.
Cause: Swollen or Torn
O-Rings
Solution: Check for O-Ring Compatibility With Media. Replace.
Problem: Excessive
or Erratic Zero Shift Under Line Pressure
Cause: Leak in System
Solution: Recheck all Fittings
Cause: Body Bolts Improperly
Torqued
Solution: Loosen & Re-torque Bolts. See Torque Guidelines.
Cause: Missing or Damaged
O-Rings
Solution: Replace as Necessary
Cause: Loose Bleed Screw
Solution: Tighten Bleed Screw to 25 In-Lb
Cause: Missing Bleed Screw
Gasket
Solution: Replace Gaskets as Required.
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