Troubleshooting, Maintenance, and Canadian Codes
Module Introduction
This chapter covers the essential skills in troubleshooting, preventive and corrective maintenance, as well as the application of Canadian codes and standards that govern the instrumentation and control technician trade. For the Red Seal exam, you must not only master diagnostic techniques but also know the precise regulatory requirements that govern the installation, modification, and maintenance of instrumentation systems.
Systematic Troubleshooting
Fundamental Principles of Troubleshooting
Troubleshooting is a logical, structured approach aimed at identifying, isolating, and correcting a failure. The most recognized method is the systematic approach, which proceeds from the general to the specific.
Key troubleshooting steps:
8.Symptom analysis — gather all available information (alarms, abnormal readings, operator reports).
9.Problem reproduction — if possible, safely reproduce the failure condition.
10.System isolation — divide the system into subsystems (sensor, transmitter, controller, final element).
11.Targeted tests — measure signals at test points (4-20 mA loop, supply voltage, loop resistance).
12.Repair or replacement — perform the correction.
13.Verification and recommissioning — confirm nominal operation and document.
The Measurement Loop: Starting Point for Diagnostics
In 80% of cases, a loop problem manifests as an erroneous reading or a missing signal. The technician must verify, in order:
| Component | Test | Expected Value |
|---|
| Power supply | Terminal voltage | 24 VDC ± 10% (typical) |
| Transmitter | Current output | 4 mA (0%) to 20 mA (100%) |
| Wiring | Loop resistance | < 250 Ω (per specifications) |
| Controller | Analog input | Corresponds to received signal |
| Final element | Position / response | Full stroke or command signal |
Loop calculation example: If a 4-20 mA transmitter is powered at 24 VDC and the total loop resistance is 500 Ω, the maximum voltage drop is:
ΔV = I × R = 0.020 A × 500 Ω = 10 V
The voltage available at the transmitter is therefore 24 V − 10 V = 14 V, which is generally sufficient for a 2-wire transmitter (typical minimum voltage: 12 V). If the resistance exceeds 600 Ω, the transmitter may no longer function properly.
Temperature Sensor Troubleshooting
Thermocouples (TC):
Check the output voltage with a millivoltmeter and compare it to the reference table (type J, K, T, etc.).
Watch for the cold junction: cold junction compensation must be active in the transmitter.
Continuity test: an open TC indicates a broken wire.
Insulation test: measure resistance between the wires and the sheath (must be > 100 MΩ).
RTDs (resistance temperature detectors):
Measure resistance at room temperature and compare to the curve (Pt100: 100 Ω at 0 °C, 138.5 Ω at 100 °C).
Verify the 3-wire or 4-wire configuration: a wiring error can introduce an error of several degrees.
Insulation test between elements and the sheath.
Pressure Transmitter Troubleshooting
Check the static pressure with a reference gauge.
Verify the 4-20 mA output with a current source and a multimeter.
Test the scale response: apply 0%, 50%, 100% of full scale and verify linearity (± 0.1% typical).
Check the seal of the process connection and the manifold.
Control Valve Troubleshooting
Check the stem position (stroke) relative to the command signal.
Test the positioner: 3-15 psi or 4-20 mA input signal, output response.
Check the supply pressure (instrument air: 20 psi or 100 psi depending on the system).
Verify hysteresis and dead band: the difference between rising and falling (typically < 1%).
Dead band calculation: If a valve receives a 50% signal on the rise and 49.5% on the fall for the same position, the dead band is 0.5%.
Preventive and Corrective Maintenance
Types of Maintenance
| Type | Description | Example |
|---|
| **Preventive** | Planned, periodic, time-based | Annual transmitter calibration |
| **Predictive** | Based on actual equipment condition | Vibration analysis, thermography |
| **Corrective** | Repair after failure | Replacement of a defective sensor |
| **Proactive** | Improvement to prevent failures | Firmware upgrade |
Calibration and Adjustment
Calibration is the operation of comparing an instrument's output to a known reference and adjusting the deviation. For the exam, you must know:
5-point calibration: 0%, 25%, 50%, 75%, 100% of scale.
Tolerances: according to the accuracy class (e.g., ± 0.1% of full scale).
Traceability: standards must be certified and traceable to national standards (National Research Council of Canada, NRC).
Pressure transmitter calibration procedure:
50.Isolate the transmitter from the process (manifold in closed position).
51.Connect a reference pressure source (deadweight tester or calibrator).
52.Power the transmitter and connect a multimeter in series.
53.Apply 0% pressure and adjust the zero (output = 4 mA).
54.Apply 100% pressure and adjust the full scale (output = 20 mA).
55.Repeat until both points are within tolerance.
56.Verify intermediate points (25%, 50%, 75%).
57.Document the results on the calibration certificate.
Pneumatic System Maintenance
Filter-regulator: drain the water reservoir, replace the filter element (typically every 6 months).
Check pressure: 20 psi for conventional instruments, 100 psi for high-capacity positioners.
Leak test: apply soapy solution to fittings and observe for bubbles.
Air dryer: check the dew point (must be below −40 °C for instruments).
Electrical System Maintenance
Ground verification: measure ground resistance (must be < 1 Ω for safety systems).
Insulation test: use a megohmmeter at 500 VDC for instrumentation cables (resistance > 100 MΩ).
Visual inspection: check for corrosion, loose wires, mechanical damage.
Battery replacement: in recorders and wireless transmitters, follow manufacturer intervals.
Canadian Codes and Standards
Canadian Electrical Code (CE Code)
The Canadian Electrical Code, Part I (CSA C22.1) is the national standard for electrical installations. For the instrument technician, the following rules are essential:
Rule 8-200: Requirements for control and instrumentation circuits. Circuits must be protected against overcurrents and overvoltages.
Rules 18-100 to 18-152: Hazardous locations (area classification). Instrumentation equipment installed in a classified area must be certified for the intended use.
Rule 26-700: Wiring of instrumentation circuits. Cables must be separated from power cables (minimum distance of 300 mm or use of separate conduits).
Rule 36-100: Grounding of instruments. All metallic enclosures must be grounded in accordance with the requirements.
CSA Standards for Instrumentation
| Standard | Title | Application |
|---|
| CSA C22.2 No 0 | General Requirements | Construction of electrical equipment |
| CSA C22.2 No 142 | Process Control Equipment | Process control equipment |
| CSA C22.2 No 213 | Non-Incendive Electrical Equipment | Equipment for non-incendive areas |
| CSA B149.1 | Natural Gas and Propane Installation Code | Installation of gas detection systems |
CSA B149.1 — Natural Gas and Propane Code
This standard is crucial for instrument technicians working on gas detection systems or burners. Key points:
Section 5.4: Gas detection — detectors must be installed according to manufacturer specifications and calibrated periodically.
Section 6.8: Combustion control systems — safety valves must be tested at least once per year.
Section 8.10: Ventilation — sensors must be placed at appropriate heights according to gas density (gases heavier than air: near the floor; gases lighter: near the ceiling).
Functional Safety Standards
The CSA C22.2 No 61508 standard (adaptation of IEC 61508) concerns the functional safety of electrical, electronic, and programmable electronic systems. For the exam, you must know:
Safety Integrity Level (SIL): levels 1 to 4, defining the probability of failure.
Risk Reduction Factor (RRF): RRF = 1 / (probability of failure).
Dangerous failure: a failure that prevents the system from performing its safety function.
SIL calculation example: If a system must have a probability of failure on demand (PFD) of 0.001, the SIL level is 3 (PFD between 0.001 and 0.0001).
Marking and Certification
Equipment installed in Canada must bear the following certification marks:
cUL (Underwriters Laboratories of Canada)
CSA (Canadian Standards Association)
cFM (Factory Mutual)
cETL (Intertek)
For hazardous areas, the marking must include the class, division, and group (e.g., Class I, Division 1, Group B).
Commissioning and Recommissioning Procedures
Commissioning an Instrumentation Loop
97.Mechanical verification: connections, supports, sensor orientation.
98.Electrical verification: continuity, insulation, polarity, grounding.
99.Pneumatic verification: supply pressure, line purging, no leaks.
100.Loop test: simulate the signal at the sensor and verify the reading at the controller.
101.Functionality test: verify alarms, interlocks, and sequences.
102.Documentation: complete commissioning forms, calibration certificates.
Work Permits and Lockout/Tagout
Lockout/tagout is mandatory before any intervention on equipment. The steps are:
105.Identify all energy sources (electrical, pneumatic, hydraulic, thermal).
106.Isolate and lock each source.
107.Dissipate residual energy (purge, discharge capacitors).
108.Attach a tag with the name, date, and reason.
109.Verify the absence of energy (de-energization test).
Exam trap: Lockout/tagout does not apply only to electricity — it applies to all forms of hazardous energy.
Documentation and Traceability
Types of Documents
Piping and instrumentation diagrams (P&IDs): standardized symbols for instruments and loops.
Loop diagrams: detail of wiring and connections for a specific loop.
Instrument data sheets: technical specifications (range, accuracy, materials).
Calibration certificates: calibration results with reference to standards.
Intervention reports: description of the problem, actions taken, parts replaced.
Standardized Symbols (ISA S5.1 / CSA Z242)
| Symbol | Meaning |
|---|
| PT | Pressure transmitter |
| TT | Temperature transmitter |
| FT | Flow transmitter |
| LT | Level transmitter |
| FV | Flow valve |
| PIC | Pressure indicating controller |
| TAH | Temperature alarm high |
Pitfalls to Avoid
121.Confusing thermocouple types: reference tables are different for each type (J, K, T, E, R, S, B). A type error gives a significant temperature error.
122.Forgetting cold junction compensation: when measuring a TC with a multimeter, the millivolt reading must be converted to temperature taking ambient temperature into account.
123.Neglecting loop resistance: a loop that is too long or has corroded connections can have excessive resistance, preventing the transmitter from functioning.
124.Ignoring hazardous area classification: installing non-certified equipment in a classified area is a violation of the CE Code and a major hazard.
125.Confusing CSA and provincial standards: the Red Seal is based on national standards (CE Code, CSA B149.1), not provincial codes.
126.Forgetting documentation: a calibration without a certificate is considered not performed.
127.Not verifying standard traceability: standards must have a valid calibration certificate and be traceable to the NRC.
128.Testing a valve without checking supply pressure: a positioner may appear defective when the instrument air is simply insufficient.
129.Confusing pressure scales: kPa, psi, bar, mmH₂O — an incorrect conversion can lead to a calibration error.
130.Not purging transmission lines: water or debris in pneumatic lines can cause intermittent failures.
Summary
Systematic troubleshooting follows a general-to-specific approach: symptoms → isolation → tests → repair → verification.
Calibration must be performed at 5 points with traceable standards and documented.
The Canadian Electrical Code, Part I (CE Code) governs electrical installations, including instrumentation circuits (Rules 8-200, 18-100, 26-700, 36-100).
The CSA B149.1 standard applies to gas and gas detection systems.
Functional safety (SIL) is a key concept for protection systems.
Lockout/tagout is mandatory before any intervention and covers all forms of energy.
Complete documentation (P&IDs, loop diagrams, certificates) is essential for traceability.
ISA S5.1 symbols are standardized and used in all instrumentation diagrams.
Final exam tip: read each question carefully and identify the applicable standard or rule before choosing your answer. Red Seal questions often test the ability to apply codes to practical situations, not just memorization of the rules.
