A Field Engineer’s Practical Guide to Finding the Real Root Cause
For field instrumentation engineers, the most difficult part of troubleshooting is often not repairing the instrument itself, but identifying the real root cause of the failure.
Very often, operators simply report:
“The instrument is faulty.”
However, they cannot clearly explain whether the problem is:
abnormal indication,
unstable signal,
control malfunction,
or incorrect measurement.
In reality, instrument and automation system failures usually fall into a limited number of categories, and once these categories are clearly understood, troubleshooting becomes much faster and more efficient.
This article summarizes common failure symptoms, high-frequency root causes, and practical field experience, providing a reliable troubleshooting framework for engineers working on site.
1. Instrument Failure Modes
Instrument failures can generally be divided into two main types:
Early Failure
Early failures occur shortly after commissioning.
These failures are typically caused by design defects, manufacturing issues, or hidden component weaknesses.
Even though electronic components undergo aging tests and inspections, a small number of defective components may still pass quality control. These “hidden defects” often become the root cause of early failures in the field.
Wear-Out (End-of-Life) Failure
All electronic and mechanical components have a finite service life.
As operating time increases, components gradually age, degrade, or wear out.
When an instrument fails after reaching or exceeding its designed service life, this is considered normal wear-out failure. In practice, many maintenance tasks involve identifying aged components and repairing or replacing them accordingly.
2. Poor Electrical Contact
Poor contact issues are directly related to electrical connections and are among the most common field problems.
Typical causes include:
oxidation or corrosion of terminals,
contact erosion due to arcing in relays and switches,
oxidized plugs,
deformed socket springs,
poor via quality in multilayer PCBs.
Such issues may cause intermittent faults, unstable signals, or abnormal heating, making them difficult to diagnose if not carefully checked.
3. Corrosion, Leakage, and Blockage
Most primary sensing elements are exposed to high temperature, high pressure, corrosive, or crystallizing process media.
Common failure points include:
impulse lines,
valves,
flanges,
fittings,
thermowell protection tubes,
sensors and transmitters installed in harsh environments.
Over time, corrosion may cause:
seized instrument housings,
damaged enclosures,
internal circuit failures,
leakage or blockage in impulse lines.
Proper material selection, isolation measures, and corrosion-resistant designs are essential to reduce such failures.
4. Sealing and Ingress Problems
A large percentage of instrument failures are caused by insufficient sealing.
Typical issues include:
improperly sealed cable entries,
loose glands,
missing or incorrectly installed gaskets,
instrument enclosures not properly tightened after maintenance.
Poor sealing allows rainwater, condensation, dust, or corrosive gases to enter the enclosure, leading to electronic failure.
In outdoor or humid installations, instruments should be:
installed in protective enclosures,
provided with adequate IP ratings,
periodically inspected and dried if condensation occurs.
5. Solder Joint Failures
Although solder joints are generally reliable, cold solder joints, cracked joints, or joint degradation can occur.
Root causes include:
manufacturing defects,
long-term thermal cycling,
high current stress in power components.
Solder joint failures are often latent, appearing only after months or years of operation, making them particularly difficult to trace.
6. Mechanical Wear
Mechanical components fail more frequently than electronic ones.
Typical examples:
actuator and control valve mechanisms,
bearings,
gears,
lubrication drying out,
broken plastic parts,
paper chart recorder drive systems.
Any component involving movement is inherently subject to wear and requires regular inspection.
7. Overheating
Electronic components are highly sensitive to temperature.
Overheating may result from:
short circuits causing excessive current,
inadequate ventilation,
high ambient temperature,
power components operating near their limits.
Excessive heat accelerates:
electrolytic capacitor degradation,
insulation breakdown,
long-term reliability loss.
8. Power Supply Issues and Electrical Surges
Incorrect supply voltage can seriously damage instruments.
Overvoltage may overheat regulators and destroy capacitors.
Undervoltage may cause unstable operation or false signals.
Additionally, lightning-induced surges and power transients can:
damage local circuits,
cause widespread system failures in severe cases.
Proper grounding, surge protection, and power conditioning are critical preventive measures.
9. Human-Induced Failures
Human error remains a significant cause of instrument failure.
Common examples:
dropping instruments during installation,
incorrect wiring or polarity reversal,
using incorrect compensation cables,
mixing signal lines,
improper adjustment of calibration elements,
dismantling instruments without understanding internal structure,
incorrect manual/auto switch positions.
Instrument damage frequently occurs during shutdowns, overhauls, and maintenance periods.
10. Interference and EMC Issues
Many instrument faults are caused by electromagnetic interference, especially in installations with:
variable frequency drives (VFDs),
high-power electrical equipment,
poor grounding practices.
Eliminating interference often requires significant effort, careful grounding design, shielding, and proper cable routing.
11. Process and External Factors
Some failures are caused by process conditions rather than the instrument itself:
refractory brick collapse damaging thermowells,
excessive vibration causing pressure gauge pointer failure,
strong electromagnetic fields affecting sensitive electronics.
If the same model or batch of instruments repeatedly fails, product quality or application suitability should be re-evaluated.
Conclusion
In field instrumentation work, blind troubleshooting is the most costly mistake.
Many problems originate in field devices but are often misattributed to control systems or software.
By clearly identifying failure symptoms and root causes, engineers can drastically reduce downtime and avoid unnecessary replacement or rework.
When an operator says “the instrument is faulty”, how do you quickly determine where to start?
Feel free to share your experience — together we can build a more complete and practical troubleshooting reference for field engineers worldwide.