Instruments Troubleshooting – Problems, Causes, Corrective Actions

This article provides an overview of troubleshooting various instruments, detailing their problems, causes, and corrective actions.

Instruments Troubleshooting

Different instruments are listed below.

• Pressure / DP / Temperature / Level Gauges
• Air Filter Regulators
• Pressure, Flow & Level Transmitters
• Thermocouple / RTD / Temperature Transmitters
• Pressure, Level, Temperature & Proximity Switches
• Vibration / Speed Sensor
• Flame Sensors
• Igniter
• Control valves, On/Off Valves & Accessories
• I to P Converter / Valve Positioner
• Position Feedback Transmitter
• Hydraulic Servo Valves
• Solenoid Valves
• Pressure Relief / Regulating Valves
• Building & Process Fire Detection Instruments
• Manual Call Points (MCPs)
• Analyzers
• Custody Transfer metering system & Gas Chromatograph
• Instrument Junction Boxes
• Weigh Bridge
• Distributed Control System
• Programmable Logic Control System

Thermocouple / RTD / Temperature Transmitters

Problems	Causes
Showing wrong / error / high / low	Loose connection at transmitter / junction box
No power / display / output	Sensor failure / Cable open
Not working	Fuse failure / Cable damaged
Malfunctioning	Element damaged
Wrong extension cable	Incorrect cable type
Sensor not responding	Sensor disconnection
Intermittent signal	Poor contact
Temperature reading fluctuating	Environmental changes
Sensor burnout	Excessive heat
Calibration error	Incorrect calibration procedure

Pressure, Level, Temperature & Proximity Switches

Problems	Causes
Not working	Manifold leak / Choke
Malfunctioning	Loose connection at switch / junction box
No power / Indication / Output	Channel fault at DCS / PLC
Incorrect switching	Faulty switch
Delayed response	Sensor lag
False triggering	Electrical noise
Noisy operation	Mechanical wear
Switch stuck	Internal blockage
Poor repeatability	Sensor aging
Mechanical damage	Physical impact

Vibration / Speed Sensors

Problems	Causes
Not working	Micro switch failure
Showing wrong / Malfunctioning	Sensor failed
No power / Indication / Output	External cable damaged
Intermittent signal	Poor connection
Sensor overheating	Environmental conditions
Signal drift	Calibration issues
High noise levels	Electrical interference
Sensor not aligned	Improper installation
Mechanical wear	Prolonged usage
Sensor contamination	Dust and debris

Flame Sensors

Problems	Causes
No flame / No power	Sensor faulty / Defective MCB
Showing fewer counts	Calibration drift
Not indicating flame	Loose connection
Sensor overheating	Excessive ambient temperature
Intermittent flame detection	Unstable flame
Sensor fouling	Dust and soot buildup
Electrical noise interference	Poor grounding
Sensor alignment issue	Misaligned sensor
Faulty signal processing	Electronics failure
Sensor aging	Degraded sensor sensitivity

Igniters

Problems	Causes
Not working	Defective ignitor
Not retracting	Mechanical blockage
No power	Cable damaged
Weak spark	Ignitor wear
Intermittent operation	Loose connections
Ignitor overheating	Excessive usage
Ignitor misalignment	Incorrect installation
Poor ignition timing	Control circuit issues
Ignitor contamination	Dirt and debris
Ignitor coil failure	Electrical failure

Control Valves & On/Off Valves & Accessories

Problems	Causes
Not working	Defective actuator
Air leak	Seal damage
Not opening/closing	Loose connection
Not opening / closing fully	Position feedback failure
Valve hunting	Volume booster failure
Valve passing	Seat damage
Gland leak	Plug / Seat / Spring damage
No feedback	Channel/card fault
No flow/output	Tubing damage
Valve stuck	Debris blockage

I to P Converter / Valve Positioner

Problems	Causes
Not working	Loose connection
Not opening/closing	Not indicated in DCS
No output	Instrument card failure
Valve not operating	Air leak / Internal choke
Positioner drift	Calibration issues
Feedback signal error	Electrical noise
Mechanical wear	Prolonged usage
Positioner overheating	Environmental conditions
Signal interference	Electrical interference
Positioner alignment issue	Incorrect installation

Position Feedback Transmitter

Problems	Causes
Not working	Channel fault
Not indicating	Alignment problem
Coil not energizing	Cable damaged
Intermittent signal	Poor connection
Feedback drift	Sensor aging
Electrical noise	Poor grounding
Feedback signal loss	Cable disconnection
Sensor overheating	Excessive ambient temperature
Calibration error	Incorrect calibration procedure
Mechanical wear	Prolonged usage

Hydraulic Servo Valves

Problems	Causes
Not working	Coil failure
No output	No power
Valve stuck	Seal damage
Sealkits damaged	Internal filter choke
Not operating	Channel fault
Intermittent operation	Electrical noise
Valve overheating	Environmental conditions
Mechanical wear	Prolonged usage
Feedback signal error	Calibration issues
Valve misalignment	Incorrect installation

Solenoid Valves

Problems	Causes
Not working	Coil failure
Malfunctioning	Valve passing
Leak/choke	Coil not energizing
Valve stuck	Internal blockage
Noisy operation	Airflow obstructions
Intermittent operation	Loose connections
Valve overheating	Excessive usage
Electrical noise interference	Poor grounding
Valve misalignment	Incorrect installation
Mechanical wear	Prolonged usage

Hazardous Gas / Chlorine Gas / Smoke / Building & Process Fire Detection Instruments

Problems	Causes
No power	Power supply failure
Air leak	Seal kit / Diaphragm damage
Sensor not responding	Sensor failure
False alarms	Electrical noise
Detector malfunctioning	Calibration drift
No alarm	Battery discharged
Sensor contamination	Dust and debris
Intermittent signal	Loose connection
Detector misalignment	Incorrect installation
Sensor aging	Degraded sensor sensitivity

Pressure Relief / Regulating Valves

Problems	Causes
Not working	Diaphragm / Seat damaged
Air/gas leak	Spring / Parts damaged
No flow/output	Internal blockage
Incorrect pressure reading	Pressure gauge damaged
Valve stuck	Debris blockage
Valve passing	Seal damage
Noisy operation	Mechanical wear
Pressure fluctuation	Calibration issues
Valve overheating	Environmental conditions
Mechanical wear	Prolonged usage

Manual Call Points (MCP)

Problems	Causes
Not working	Micro switch failure
Malfunctioning	Loose connection
No alarm	No communication with repeater panel
Glass broken	Physical impact
Intermittent operation	Electrical noise
No power	Power supply failure
Faulty signal transmission	Cable damage
False alarms	Sensor aging
Mechanical wear	Prolonged usage
Misalignment	Incorrect installation

Analysers

Problems	Causes
Not working	Analyser failure
Malfunctioning	Loop cable damaged
Not matching with lab readings	Calibration drift
No local display	Sensor not clean
No indication in DCS / PLC	Channel fault
Sensor drift	Sensor aging
Electrical noise interference	Poor grounding
Intermittent signal	Loose connection
Sensor contamination	Dust and debris
Signal loss	Cable disconnection

Custody Transfer / Check Metering System & Gas Chromatograph

Problems	Causes
Not working	Sample line choke
No flow/output	Fuse / Power supply card failure
Calibration gas leak	Isolation valve problem
Carrier gas leak	Rotameter stuck
No sample gas	Valve passing problem
No carrier gas	Seal kit damaged
Red LEDs glowing	Internal filter choke
Readings not matching	Calibration disturbed
No power	Sensor not clean / failed
Showing error	Sampling probe issue

Pressure / DP / Temperature / Level Gauges

Problems	Causes
Not working	Bourdon tube damaged
Glass broken	Impact damage
Showing zero / span / error	Internal parts dislocated/damaged
Needle fallen	Poor assembly
Gauge leaking	Thermowell damaged
Needle hunting	Overtightening / Lack of cleaning
Inconsistent readings	Temperature fluctuations
Gauge vibration	No anti-vibration liquid
View glass not visible	Lack of guard for LG glass
Orientation not proper	Improper installation

Air Filter Regulator (AFR)

Problems	Causes
Not working / No air output	Diaphragm damaged
Sheath / Capillary punctured	Physical damage
Air leak	Loose fittings
Drain valve not working	Internal parts damaged/dislocated
Adjustment knob not working	Internal blockage
Pressure gauge fluctuating	Faulty gauge
Noisy operation	Airflow obstructions
Low output pressure	Regulator set too low
High output pressure	Regulator set too high
Gauge not responding	Gauge failure

Pressure, Flow & Level Transmitters

Problems	Causes
Showing wrong / error / high / low	Loose connection at transmitter / junction box
Knob / Drain valve stuck	Debris in valve
Impulse tubing leak	Tubing damaged
Fitting choke	Blockage in fitting
Diaphragm punctured	Physical damage
No power / Indication / Output	AI channel fault at DCS / PLC
Incorrect calibration	Calibration drift
Signal interference	Electrical noise
Moisture ingress	Poor sealing
Sensor drift	Sensor aging

Instrument Junction Boxes

Problems	Causes
Instruments not working	Loose connection
Not indicating / Showing error	Terminal blocks / Screws damaged
Display coming & going	Water entry
Intermittent power loss	Faulty wiring
Noisy operation	Electrical noise
Overheating	Poor ventilation
Moisture ingress	Poor sealing
Signal interference	Poor grounding
Mechanical damage	Physical impact
Loose terminals	Vibration

Distributed Control System (DCS)

Problems	Causes
Battery discharged	IO cards / CPUs failure
Red LEDs glowing	Channel fault
Reading showing stars/zeros	Loose connection
Not rebooting	Momentary malfunction
Display hanged	Defective power supply
Display coming & going	HMI / OT / SMPS fault
No display	Earthing / Grounding problem
Reading showing “—“	Communication cable problem
Parameters not updating	Software bug / Hardware problem
Time mismatch	GPS problem or time sync issue

Programmable Logic Controllers (PLC)

Problems	Causes
Showing wrong / error / high/low	IO card / CPU failure
Red LEDs glowing	Channel fault
Reading showing stars/zeros	Loose connection
Not rebooting	Battery discharged
Display hanged	Defective power supply
Display coming & going	HMI / OT / SMPS failure
No display	Earthing / Grounding problem
Reading showing “—“	Communication cable problem
Parameters not updating	Software bug / Hardware problem

Weigh Bridge

Problems	Causes
Not working	Fuse / Power card failure
Not showing reading	Load cell / Electronic card failure
Showing wrong / error / high / low	Servicing / Cleaning required
Mismatch with flow meter	Calibration setting disturbed
Intermittent readings	Loose connection
Overload indication	Load cell damaged
Signal drift	Sensor aging
No power	Power supply failure
Mechanical wear	Prolonged usage
Calibration error	Incorrect calibration procedure

Corrective Actions

Some of the correction actions to be carried out during instrument troubleshooting are shown below.

• Loop tightening
• Cleaning
• Lubrication
• Servicing
• Adjustment
• Alignment
• Calibration
• Configuration
• Rebooting
• Defective parts replacement
• cables check
• Instruments Replacement etc.

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