Temperature Transmitter Calibration SOP

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• Document control header (SOP INST 003)
• Purpose, scope and references
• Safety, tools and prerequisites
• Numbered step by step procedure
• Acceptance criteria and records
• Approval block for sign off

1. Purpose

To verify that temperature transmitters convert the sensor signal to the correct 4 to 20 mA output within tolerance.

2. Scope

Temperature transmitters with Pt100 (2, 3 or 4 wire) or thermocouple inputs and 4 to 20 mA or HART output. Sensor checks are covered in a separate SOP.

3. References

• IEC 60751 (Pt100 tables)
• IEC 60584-1 (thermocouple tables)
• Transmitter manual and data sheet

4. Responsibilities

• Instrument technician: carries out the work and records results.
• Instrument engineer or supervisor: reviews and approves the records.
• Operations: grants the permit, isolates the process and returns the equipment to service.

5. Safety Precautions

• Work only under a valid permit to work and follow the site isolation (lockout tagout) procedure.
• Wear the PPE required for the area: safety helmet, glasses, gloves and safety shoes as a minimum.
• In hazardous areas use certified or intrinsically safe test equipment, or obtain a gas free certificate and hot work permit.
• Inform the control room before starting, and before returning the instrument to service.
• Open transmitter heads in hazardous areas only when the area is gas free or the circuit is intrinsically safe and the permit allows it.

6. Tools and Equipment

• RTD and thermocouple simulator / calibrator with cold junction compensation
• mA meter or documenting calibrator
• HART communicator
• Correct thermocouple extension or compensating wire for the simulator connection

7. Prerequisites

• Loop in manual and trips bypassed as approved.
• Sensor type, wiring and range confirmed from the data sheet.

8. Procedure

8.1 Preparation

1. Disconnect the sensor wires from the transmitter and label them.
2. Connect the calibrator to the input terminals using the same wiring (3 wire for a 3 wire RTD; thermocouple wire of the same type for thermocouples).
3. For thermocouples, use the calibrator's internal cold junction compensation, or simulate the mV value directly with the transmitter's CJC disabled as per the manual.

8.2 As found test

1. Simulate 0, 25, 50, 75 and 100 % of the calibrated range and record the output.
2. Record the simulated value (Ω or mV) and the expected mA.
3. Calculate errors in % of span.

8.3 Adjustment and as left

1. If out of tolerance, perform the input (sensor) trim and/or output trim as described in the manual.
2. Repeat the test and record the as left values.

8.4 Return to service

1. Reconnect the sensor wires exactly as before; check terminal tightness.
2. Close the head cover with its seal in place.
3. Confirm a sensible temperature reading in the DCS.

9. Acceptance Criteria

• As left errors within tolerance (typically ± 0.25 % of span).
• Sensor reconnected and reading correct.

10. Records

Related tools

This is a generic procedure. Adapt it to your site permit system, the manufacturer instructions and your quality system before use.

Frequently Asked Questions