The detection method of thermal instruments is mainly determined according to its measurement principle and characteristics, usually including direct measurement method, indirect measurement method, and a variety of specific detection techniques and steps. The following is a detailed summary of the detection methods of thermal instruments:

1. Direct measurement method
The direct measurement method refers to the measurement method that directly compares the measured value with the measurement unit, or uses a pre-calibrated measuring instrument to measure, so as to obtain the measurement result. For example, use a spring tube pressure gauge to directly measure the medium pressure in the container, or use a glass tube thermometer to directly measure the medium temperature.

2. Indirect measurement method
The indirect measurement method is to obtain the measurement result by directly measuring other variables that have a certain functional relationship with the measured value, and then calculate according to the functional relationship. For example, the measurement of the main steam flow in a power plant is to first measure the temperature, pressure, and differential pressure signal output by the standard throttling device of the main steam, and then calculate the mass flow of the main steam.

3. Specific detection technology
Thermocouple detection technology:
Overview: Thermocouple is one of the commonly used temperature sensing elements in industry. It converts temperature signals into thermoelectric potential signals. With display instruments and transmitters, it can realize temperature measurement and signal conversion.
Technical requirements: The allowable error of thermoelectric potential of the thermocouple (within the specified temperature range, when the reference end temperature is 0°C) should comply with relevant regulations.
Calibration: Put the calibrated thermocouple and the standard thermocouple together in the middle of the calibration furnace, and carry out heating, constant temperature, measurement, and recording processes to ensure the calibration quality.
Thermocouple detection technology:
Overview: Thermocouple is also a commonly used temperature-measuring element. Commonly used ones are platinum thermocouples and copper thermocouples, such as Pt100, Cu50, etc.
Inspection and verification: including appearance inspection, inspection and replacement of temperature sleeves at easily worn parts, inspection and testing of compensation wires and measurement circuits, component verification, and other steps.
IV. Inspection steps and precautions
Inspection steps:
Preparation stage: Ensure that the labels and numbers of the instruments are correct, clear, and complete; check the fuse capacity and on-off condition of the fuse; ensure that the electrical wiring of the instrument is correct; check the insulation of the line and its equipment.
Measurement stage: Select appropriate measurement methods and instruments according to the measurement principles and characteristics of the instruments; perform measurement operations according to the operating procedures; record measurement data, and perform data processing and analysis.
Judgment stage: According to the measurement results and error range, judge whether the instruments are qualified or need to be adjusted.
Precautions:
During the inspection process, ensure the safety of the operator and comply with relevant safety regulations and operating procedures.
Select the appropriate measurement range and accuracy to avoid excessive measurement errors.
Before the inspection, the instruments should be fully preheated and calibrated to ensure the accuracy of the measurement results.
During the inspection process, pay attention to the operation status of the instruments and the stability of the measurement data, and promptly discover and handle abnormal situations.
In summary, the inspection methods of thermal instruments involve many aspects, including direct measurement methods, indirect measurement methods, and specific inspection techniques and steps. Through scientific testing methods and processes, the accuracy and reliability of measurement results can be ensured, providing strong support for industrial production and quality control.