Calibration, Testing, and Commissioning

Chapter Objectives

This chapter covers the knowledge and skills required for the Red Seal exam concerning the calibration, testing, and commissioning of instruments and control systems. You will find essential definitions, standardized procedures, uncertainty calculations, Canadian regulatory requirements, and common pitfalls to avoid.

Fundamental Definitions

Calibration: An operation that establishes, under specified conditions, the relationship between the values indicated by a measuring instrument and the corresponding values of a known quantity (standard). Calibration does not modify the instrument; it documents its behaviour.

Adjustment (or trimming): The action of bringing an instrument to a state of operation corresponding to a specified accuracy. Adjustment physically modifies the instrument (zero screws, potentiometers, etc.).

Verification: Confirmation through tangible evidence that specified requirements have been met. Verification does not necessarily include calibration.

Traceability: The property of a measurement result whereby the result can be related to a national or international standard through an unbroken chain of comparisons, each having a stated uncertainty.

Measurement Uncertainty: A non-negative parameter that characterizes the dispersion of values attributed to a measurand. It is expressed in units of measurement or as a percentage of reading.

Error: The difference between the value indicated by the instrument and the true (or conventionally true) value of the measurand. Total error = systematic error + random error.

Drift: A slow, continuous variation in a metrological characteristic of an instrument over time, under constant ambient conditions.

Canadian Standards and References

Standard	Application
Canadian Electrical Code, Part I	Electrical safety requirements for installations (Rule 8-200 for grounding conductors)
CSA B149.1	Natural gas and propane code — requirements for burner systems and their controls
CSA Z432	Machinery safeguarding — applicable to safety testing
ISO 9001	Quality management systems — requirements for documented calibration procedures
ISO 10012	Measurement management systems — requirements for measurement processes
NIST SP 800-82	Industrial control system security (reference for cybersecurity during commissioning)

The Canadian Electrical Code, Part I (C22.1-21) applies to all electrical installations in Canada. For instrumentation work, Rule 8-200 requires that all equipment be grounded in accordance with manufacturer specifications and code requirements. Rule 18-100 addresses hazardous locations and imposes strict requirements for instruments installed in these areas.

Calibration Procedures

Calibration Preparation

Before any calibration operation, you must:

18.Identify the instrument: serial number, tag, location, associated control loop.

19.Obtain the calibration procedure: manufacturer's document or approved internal procedure.

20.Verify ambient conditions: temperature, humidity, vibrations — they must be within specified limits.

21.Select the standard: the standard must have an uncertainty at least 4 times better than the accuracy of the instrument being calibrated (TUR ratio ≥ 4:1).

22.Verify the validity of the standard: calibration certificate currently valid, no physical damage.

23.Prepare the equipment: power supply, multimeter, HART communicator, pressure pump, temperature bath, etc.

Test Points

A complete calibration typically includes 5 measurement points (0%, 25%, 50%, 75%, 100%) in both directions (up-scale and down-scale). The number of points may vary according to internal standards or the type of instrument.

Error Calculation

For each test point:

Error (%) = [(Reading − Standard Value) / (Span)] × 100

Example: A 0–100 kPa pressure transmitter indicates 50.5 kPa when the standard indicates 50.0 kPa.

Error = [(50.5 − 50.0) / 100] × 100 = 0.5%

If the specified accuracy is ±0.25% of span, the instrument is out of tolerance and must be adjusted.

Hysteresis

Hysteresis is the maximum difference between up-scale and down-scale readings at the same input point. It is calculated as:

Hysteresis = |Up-scale reading − Down-scale reading|

Hysteresis is a mechanical characteristic (friction, backlash) and cannot be corrected by a simple zero or span adjustment.

Non-linearity

Non-linearity is the maximum deviation between the instrument's actual curve and the ideal straight line (or reference curve). It is expressed as a percentage of span.

Calibration of Specific Instruments

Pressure Transmitters

40.Zero calibration: apply atmospheric pressure (or reference pressure), adjust zero.

41.Span calibration: apply full-scale pressure, adjust gain (span).

42.Linearity check: apply intermediate points (25%, 50%, 75%).

43.Hysteresis check: perform down-scale readings and note the differences.

For a capacitive cell transmitter (such as a Rosemount 3051), adjustment is done via HART communication or local buttons. The "zero and span" adjustment procedure must be performed in order: first zero, then span, then re-check zero (because span adjustment often affects zero).

Temperature Transmitters

Thermocouples: Calibration is performed by comparing the thermocouple output to a reference thermometer in a temperature bath. Typical points are 0 °C (ice bath), 100 °C (boiling water), and intermediate points depending on the operating range.

RTDs (Pt100): The resistance-temperature relationship is defined by IEC 60751. For a Pt100, at 0 °C, R = 100 Ω; at 100 °C, R = 138.51 Ω. The Callendar-Van Dusen equation is used for precise calculations:

R(t) = R₀ [1 + A·t + B·t² + C·(t−100)·t³] for t between −200 °C and 0 °C

R(t) = R₀ [1 + A·t + B·t²] for t between 0 °C and 850 °C

Where: A = 3.9083 × 10⁻³ °C⁻¹, B = −5.775 × 10⁻⁷ °C⁻², C = −4.183 × 10⁻¹² °C⁻⁴

Control Valves

Calibrating a control valve involves verifying:

53.The start point: the valve should begin to open at a signal of 3–5% (for a 4–20 mA signal).

54.The end point: the valve should be fully open at 95–100% of the signal.

55.Linearity: valve travel should be proportional to the input signal.

56.Hysteresis: the difference between opening and closing travel for the same signal.

57.Leakage: verify the leakage rate in the closed position according to the leakage class (Class I to VI per ANSI/FCI 70-2).

Flow Transmitters

For a magnetic flowmeter: verify zero (no flow, pipe full), then simulate a known flow or use a calibration loop. The K-factor (pulses per litre) must be verified.

For a Vortex flowmeter: verify the output frequency for a known flow. The relationship is: f = K × Q where f is the frequency in Hz, K is the K-factor in pulses per litre, and Q is the flow rate in L/s.

Uncertainty Calculations

Combined Uncertainty

Combined uncertainty (u_c) is calculated as the square root of the sum of the squares of the individual uncertainties:

u_c = √(u₁² + u₂² + u₃² + ...)

Example: A pressure transmitter calibration uses a standard with an uncertainty of ±0.05% of reading, a multimeter with ±0.02% of reading, and a pressure source with ±0.03% of span.

u_c = √(0.05² + 0.02² + 0.03²) = √(0.0025 + 0.0004 + 0.0009) = √0.0038 = 0.0616%

Expanded Uncertainty

Expanded uncertainty (U) is obtained by multiplying the combined uncertainty by a coverage factor k (typically k = 2 for a 95% confidence level):

U = k × u_c

TUR Ratio (Test Uncertainty Ratio)

TUR = Standard Accuracy / Instrument Accuracy

The minimum recommended TUR is 4:1. If the TUR is less than 4:1, the calibration is considered marginal and the uncertainty must be explicitly calculated.

Commissioning Tests

Commissioning Plan

Commissioning an instrumentation system follows a logical sequence:

76.Visual inspection: verification of physical installation, connections, supports, and labels.

77.Loop verification: cable continuity, polarity, insulation, grounding.

78.Power supply: verification of supply voltages (24 VDC, 120 VAC, etc.) before powering up the instruments.

79.Individual testing: calibration and testing of each instrument.

80.Loop testing: verification of the response of the entire loop (sensor → transmitter → controller → valve).

81.Functional testing: simulation of process conditions to verify alarms, interlocks, and sequences.

82.Safety testing: verification of safety instrumented functions (SIFs) per IEC 61511.

Loop Testing

Loop testing involves verifying that the signal travels correctly through the entire control loop. The typical procedure:

85.Inject a known signal at the transmitter input (for example, 50% of span).

86.Verify the reading at the controller (DCS or PLC): it should correspond to 50%.

87.Verify the output to the final element: the valve should be positioned at 50% of its travel.

88.Document the results: injected values, read values, deviations, status (accepted/rejected).

Interlock Testing

Safety interlocks must be tested individually and in combination. The procedure:

91.Obtain the work permit and follow the lockout/tagout procedure.

92.Simulate the trip condition (high pressure, low temperature, etc.).

93.Verify that the safety action occurs: valve closure, motor shutdown, alarm activation.

94.Verify the response time: it must be less than the time required by the safety analysis.

95.Restore the system and document the test.

Communication Testing

For smart instruments (HART, Foundation Fieldbus, Profibus):

98.Verify communication: the communicator or system must recognize the instrument.

99.Verify parameters: tag, units, range, signal type.

100.Verify diagnostics: no active alarms, no internal faults.

101.Back up the configuration before making any changes.

Documentation

Calibration Certificate

A calibration certificate must contain:

Instrument identification (manufacturer, model, serial number, tag)

Identification of the standard used (serial number, reference certificate)

Ambient conditions (temperature, humidity)

Date of calibration and validity date

Measurement results (table of points, calculated errors)

Measurement uncertainty

Name and signature of the calibrator

Reference to the procedure used

Loop Sheet

The loop sheet documents all elements of a control loop: instruments, cables, terminal blocks, power supply, and configuration parameters. It is essential for commissioning and troubleshooting.

Calibration Register

The calibration register is a tracking system that indicates for each instrument: the date of the last calibration, the date of the next calibration, the status (compliant/non-compliant), and the history of interventions.

Lockout/Tagout and Safety

Before any calibration or testing work on an instrument in service, you must:

119.Obtain a work permit (hot work permit, cold work permit, confined space entry permit as applicable).

120.Lock out the equipment: isolate the instrument from the process (isolation valves), disconnect the electrical supply, lock and tag.

121.Verify the absence of pressure, temperature, and product before disassembling.

122.Use appropriate personal protective equipment.

The lockout/tagout procedure is governed by the Canada Labour Code (Part XIX) for federal installations and by provincial legislation for other installations. The fundamental principle: each person working on the equipment must place their own lock.

Pitfalls to Avoid

125.Confusing calibration and adjustment: calibration is a documented comparison; adjustment is a modification. An instrument can be calibrated without being adjusted.

126.Neglecting the adjustment order: always adjust zero before span, then re-check zero. A span adjustment often affects zero.

127.Using a standard with insufficient TUR: the ratio must be at least 4:1. A standard at ±0.5% cannot calibrate an instrument at ±0.25%.

128.Forgetting hysteresis: a hysteresis error cannot be corrected by adjustment. If hysteresis exceeds tolerance, the instrument must be repaired or replaced.

129.Not accounting for ambient temperature: most instruments have a specified thermal drift (for example ±0.02%/°C). A calibration performed at 40 °C will not be valid at 20 °C.

130.Ignoring mounting conditions: a pressure transmitter mounted with a damaged O-ring or a partially open valve will give erroneous readings.

131.Not documenting: an undocumented calibration is a calibration not performed. Every intervention must be traceable.

132.Confusing percentage of reading and percentage of span: an error of 1% of reading is not the same as an error of 1% of span. For a 0–100 kPa instrument, 1% of reading at 20 kPa = 0.2 kPa; 1% of span = 1 kPa.

133.Forgetting reference conditions: accuracy specifications are given for reference conditions (temperature 20 °C, nominal supply, etc.). Outside these conditions, accuracy degrades.

134.Not verifying alarms and interlocks: during commissioning, alarms and interlocks must be tested in simulation, not just visually checked.

Summary

Calibration is a documented comparison between an instrument and a traceable standard; adjustment is a modification of the instrument.

The TUR ratio must be ≥ 4:1 for a valid calibration.

Error is calculated as a percentage of span: Error (%) = [(Reading − Standard) / Span] × 100.

Combined uncertainty is calculated as the square root of the sum of the squares of the individual uncertainties.

Hysteresis and non-linearity are distinct characteristics that cannot be corrected by simple adjustment.

Commissioning follows a sequence: visual inspection, loop verification, power supply, individual testing, loop testing, functional testing, safety testing.

The Canadian Electrical Code, Part I and CSA B149.1 are the main normative references for instrumentation work in Canada.

Documentation is mandatory: calibration certificates, loop sheets, registers.

Lockout/tagout is mandatory before any intervention on an instrument in service.

Safety interlocks must be tested individually and in combination, with response time verification.

Self-Assessment Questions

147.A 0–200 kPa pressure transmitter indicates 102.5 kPa when the standard indicates 100.0 kPa. Calculate the error as a percentage of span.

148.A standard has an uncertainty of ±0.1% and the instrument to be calibrated has an accuracy of ±0.5%. Is the TUR acceptable?

149.What is the difference between hysteresis and non-linearity?

150.Why must you adjust zero before span when trimming a transmitter?

151.What are the three main steps of the lockout/tagout procedure?

152.A type K thermocouple indicates 250 °C. The measured voltage is 10.151 mV. Given that the reference table gives 10.153 mV for 250 °C, what is the error in °C?

153.Which Canadian standard governs natural gas and propane installations?

154.A Vortex flowmeter has a K-factor of 10 pulses per litre. At a flow rate of 5 L/s, what output frequency do you expect?

155.During a loop test, you inject 12 mA (50% of span) at the transmitter. The controller displays 51%. What is the error as a percentage of span?

156.Why is the minimum recommended TUR 4:1?

Calibration, Testing, and Commissioning