How to calibrate a temperature sensor in the field

Temperature sensors are often calibrated to ensure product quality, maintain proper flow or to meet safety requirements. Degradation of sensors, which can be exposed to temperature cycling as well as vibration, can be accounted for during the tests.

Indeed, the cost of not calibrating temperature equipment can be extreme—inferior products, unscheduled equipment downtime, regulatory penalties and even potentially tragic accidents with tremendous legal liability.

The type of sensor used often depends on accuracy requirements. For example, RTDs (resistance temperature detectors) and PRTs (platinum resistance thermometers) are used when a high degree of accuracy is important. Thermocouples are inexpensive and can be used over wider temperature ranges but are less accurate than PRTs or RTDs.

Whether a PRT, TC or RTD, testing the sensor is an important practice in complete temperature calibration. Testing the sensor and transmitter together verifies sensor and transmitter electronics adding a test of the control system input completes a full loop calibration.

Fluke offers temperature calibration tools well suited to the rigorous demands of industry, including specialty handheld temperature calibrators and the more advanced — but still portable — dry-block metrology wells with accredited calibration accuracy.

Intrinsically safe "Stik" thermometers, such as the Fluke 1551A, is precise enough to act as a reference thermometer and were designed with the oil and gas, chemical processing and other potentially explosive environments in mind.

Pairing a Fluke dry well with a handheld documenting calibrator allows for a complete field temperature calibration solution. You can test the entire tempeloop—the temperature sensor and all measurement electronics—in order to optimize performance.

Most advanced Fluke documenting process calibrators can also test and calibrate both temperature and pressure instruments. That keeps the number of instruments a technician needs to carry to a minimum.

What is Temperature Calibration?

Temperature calibration is the process of verifying and adjusting the accuracy of a temperature measurement device, such as a thermometer, temperature sensor, or temperature probe. This procedure ensures the device provides accurate temperature readings over its operating range. Calibration is critical in industries like manufacturing, pharmaceuticals, food processing, and HVAC, where precise temperature control is essential for product quality, safety, and regulatory compliance. Regular temperature calibration helps maintain the reliability of temperature-sensitive processes, reduces errors, and ensures measurement consistency. Calibration typically involves comparing the device's readings under test with those of a reference standard with a known and traceable accuracy.

How to Check Calibration Temperature?

To check the calibration of a temperature sensor, follow these detailed steps:

1. 1. Prepare a Stable Environment: Ensure that the calibration process is conducted in a stable environment, free from temperature fluctuations and drafts, which can affect the accuracy of the measurements.
2. Use a Reference Standard: Obtain a reference temperature standard, such as a calibrated reference thermometer, dry-block calibrator, or temperature bath. Ensure that the reference standard is traceable to a national or international standard.
3. Position the Sensor and Reference: Place the temperature sensor and the reference standard nearby to ensure they measure the same environment. Allow both devices to reach thermal equilibrium.
4. Record Initial Readings: Once the temperature sensor and reference standard have stabilized, take initial readings from both.
5. Compare and Analyze: Compare the readings from the temperature sensor with the reference standard. Note any discrepancies and calculate the difference. This comparison helps identify any calibration drift or inaccuracies in the sensor.
6. Adjust the Sensor: If the temperature sensor shows a significant deviation from the reference standard, adjust it according to the manufacturer's calibration procedures. This may involve software adjustments or physical calibration adjustments on the sensor itself.
7. Document the Results: Record the calibration results, including the date, initial readings, adjustments made, and final readings. This documentation is essential for traceability and future calibration reference.

How Do You Calibrate Temperature Sensors?

Calibrating temperature sensors involves a series of steps to ensure accurate readings. Here's a detailed guide:

1. Select Calibration Equipment: Choose the appropriate calibration equipment for your temperature sensor. This can include a dry-block calibrator, a liquid bath, a temperature chamber, and a highly accurate reference thermometer.
2. Identify Calibration Points: Determine the temperature points at which the sensor will be tested. These points should cover the sensor's entire operating range and include critical temperatures relevant to your application.
3. Stabilize the Sensor: Place the temperature sensor in the calibration equipment and allow it to stabilize at the first calibration point. Stabilization ensures the sensor and the calibration medium reach thermal equilibrium.
4. Record Readings: Once the sensor is stable, record its reading and the reference thermometer's reading at that temperature.
5. Repeat for All Points: Repeat each calibration point's stabilization and recording process. This typically includes low, medium, and high points within the sensor's operating range.
6. Analyze Data: Compare the sensor's readings with the reference thermometer at each calibration point. Calculate the deviation for each moment to understand the sensor's accuracy across its range.
7. Adjust Sensor Calibration: If discrepancies are found, adjust the sensor's calibration settings per the manufacturer's guidelines. This might involve entering correction factors into the sensor's software or making physical adjustments.
8. Recheck and Verify: After making adjustments, recheck the sensor readings at all calibration points to verify the Calibration's accuracy.
9. Document the Process: Thoroughly document the calibration process, including all readings, adjustments, and final results. This documentation is essential for compliance with industry standards and for future reference.

How to Calibrate a Temperature Probe?

Calibrating a temperature probe requires specific steps to ensure its accuracy. Follow these detailed instructions:

1. Gather Calibration Tools: Obtain a calibration setup that includes a temperature bath, a dry-block calibrator, a temperature chamber, and a reference thermometer with known accuracy.
2. Insert the Probe and Reference: Place the temperature probe and the reference thermometer in the calibration medium. Ensure they are positioned to measure the exact temperature environment.
3. Set Desired Calibration Points: Set the calibration medium to the first desired temperature point. Typical points include ice water (0°C/32°F), boiling water (100°C/212°F), and intermediate temperatures relevant to your application.
4. Allow Stabilization: The probe and the reference thermometer stabilize at the set temperature point, ensuring that both the probe and the medium reach thermal equilibrium.
5. Record and Compare Readings: Once stabilized, record the readings from the temperature probe and the reference thermometer and compare them to determine any discrepancies.
6. Adjust Calibration: If the probe and the reference thermometer differ significantly, adjust the probe according to the manufacturer's calibration instructions. This may involve using calibration software or changing the probe's physical settings.
7. Repeat for Additional Points: Repeat the process for all identified calibration points to ensure the probe's accuracy across its entire operating range.
8. Document Calibration Results: Record all calibration data, including initial, adjustments, and final readings. This documentation is critical for traceability and compliance with industry standards.

How to Test a Temperature Sensor with a Multimeter?

Testing a temperature sensor with a multimeter involves checking its resistance to ensure it operates correctly. Here's how to do it:

1. Turn Off Power: To avoid electrical hazards, ensure the device or system connected to the temperature sensor is powered off.
2. Disconnect the Sensor: Disconnect the temperature sensor from the system to isolate it for testing.
3. Set Multimeter to Resistance Mode: Set the multimeter to the resistance (ohms) setting, typically denoted by the Ω symbol.
4. Measure Sensor Resistance: Connect the multimeter probes to the temperature sensor terminals. Ensure good contact to get an accurate measurement.
5. Compare Resistance Values: Refer to the sensor's datasheet to find the expected resistance values at a given temperature (usually room temperature). Compare the measured resistance with the specified value.
6. Check for Consistency: If the resistance value matches the expected value, the sensor is likely functioning correctly. If it is significantly different, the sensor may be faulty or require recalibration.
7. Test at Different Temperatures: For a more comprehensive test, measure the sensor's resistance at different known temperatures and compare it with the datasheet values. This can help identify any non-linearities or faults in the sensor.
8. Document Findings: Record all measurements and observations during testing for future reference and troubleshooting.