Here is a specific case of thermocouple calibration:

Case background

A chemical enterprise decides to calibrate the K-type thermocouples it uses in order to ensure the accuracy of temperature measurement in the production process. The production temperature range of this enterprise is usually between 0℃ and 500℃.

Calibration preparation

1. Equipment selection:

- Select a high-precision constant temperature bath as the temperature source. Its temperature stability is within ±0.1℃ and can cover the required calibration temperature range.

- Prepare a digital multimeter with high measurement accuracy and stability for measuring the electromotive force generated by the thermocouple.

- Use a standard K-type thermocouple with a higher precision level as the reference standard.

2. Check equipment status:

- Preheat and test the stability of the constant temperature bath to ensure that it can stably output temperature at different temperature points.

- Check the battery power and measurement function of the digital multimeter to see if they are normal.

- Check the appearance of the standard thermocouple and the calibrated thermocouple to ensure there is no damage.

Calibration process

1. Connect equipment:

- Insert the measuring ends of the standard thermocouple and the calibrated thermocouple into the constant temperature bath, and try to keep the insertion depth and position consistent.

- Correctly connect the output ends of the thermocouples to the digital multimeter.

2. Temperature setting:

- Start from 0℃ and increase the temperature of the constant temperature bath in intervals of 50℃ until 500℃.

- At each temperature point, after waiting for the temperature of the constant temperature bath to stabilize (usually 15 to 20 minutes), record the electromotive force values of the standard thermocouple and the calibrated thermocouple.

3. Data recording and calculation:

- Convert the recorded electromotive force values into corresponding temperature values according to the electromotive force and temperature relationship table of the standard thermocouple.

- Calculate the error of the calibrated thermocouple at each temperature point, that is, subtract the temperature value of the standard thermocouple from the temperature value of the calibrated thermocouple.

Data analysis and processing

1. Draw a calibration curve:

- Use temperature as the abscissa and error as the ordinate to draw the calibration curve of the calibrated thermocouple.

- Observe the trend of the curve to judge the linearity and stability of the calibrated thermocouple.

2. Error analysis:

- Analyze the distribution of errors and determine the maximum, minimum, and average values of the errors.

- If the error exceeds the allowable range, further analyze the reasons, which may be thermocouple aging, damage, or inaccurate calibration equipment.

3. Error correction:

- According to the results of error analysis, correct the errors of the calibrated thermocouple. If the error is small, it can be compensated by software correction in the measurement system; if the error is large, hardware adjustment or replacement of the thermocouple may be required.

Calibration report

1. Compile a calibration report, including the purpose, scope, equipment, steps, results, and conclusions of the calibration.

2. Attach the data tables and calibration curve charts recorded during the calibration process.

3. The calibration personnel and review personnel sign to confirm to ensure the accuracy and reliability of the calibration results.

Through this calibration case, the chemical enterprise can timely discover and solve the error problems in thermocouple measurement, improve the accuracy of temperature measurement, and thus ensure the stability of the production process and the reliability of product quality.