Check the working environment: The self - calibration should be carried out in a stable environment. The ambient temperature should be within the range specified in the PR235 manual (usually 15 - 35°C), and the relative humidity should be controlled between 20% - 80% to avoid the impact of extreme temperature and humidity on the calibration results. At the same time, ensure that there is no strong electromagnetic interference around, such as high - power motors, transformers, etc., and keep the calibration site clean and tidy.

Prepare necessary tools and materials: Prepare standard instruments that meet the accuracy requirements, such as high - precision multimeters, standard resistors, and standard signal generators. These standard instruments should have valid calibration certificates. In addition, prepare appropriate connecting cables, screwdrivers, and cleaning tools. It is also necessary to check the battery power of the PR235 or ensure a stable power supply to avoid power failure during calibration.

Familiar with the PR235 manual: Before starting self - calibration, carefully read the relevant chapters of the PR235 manual to understand the specific requirements, operation methods, and precautions for self - calibration. Pay special attention to the calibration points and range settings suitable for on - site self - calibration.

Turn on the PR235 and let it warm up according to the requirements of the manual. Generally, the warm - up time is 15 - 30 minutes. This step is crucial because the electronic components inside the PR235 need a certain period of time to reach a stable working state, and insufficient warm - up time will lead to unstable calibration results.

During the warm - up period, connect the standard instruments to the PR235 correctly according to the calibration items (such as voltage, current, resistance). Ensure that the connection is firm and the polarities are correct to avoid short circuits or incorrect signal transmission.

After the warm - up is completed, operate the PR235 to enter the self - calibration mode. The specific operation method may vary depending on the model of the PR235. Usually, it can be entered by pressing a combination of keys or through the menu selection on the operation interface. Refer to the manual for the exact steps.

In the self - calibration mode, select the calibration function to be performed, such as voltage calibration, current calibration, or resistance calibration, according to the actual needs.

Set the calibration point: According to the manual, set the PR235 to the specified calibration points. For example, when calibrating the 4 - 20mA current output, the calibration points may include 4mA, 12mA, and 20mA.

Compare with standard instruments: For each calibration point, read the value displayed by the PR235 and the value measured by the standard instrument. Record the two sets of data accurately.

Adjust the PR235: If the difference between the PR235's display value and the standard instrument's measured value exceeds the allowable error range, adjust the PR235 according to the prompts in the self - calibration mode. The adjustment method may involve inputting the standard value measured by the standard instrument into the PR235, and the device will automatically correct its internal parameters.

Repeat the verification: After adjustment, re - measure the calibration point to confirm that the PR235's display value is within the allowable error range. If not, repeat the adjustment until the requirement is met.

Perform the above steps for each calibration point of all parameters that need to be calibrated.

After completing all self - calibration operations, exit the self - calibration mode. Select some random points within the measurement range of the PR235 for verification. Use the standard instruments to measure the output or measurement values of the PR235 at these points to check whether they are within the specified accuracy range.

If the verification results are all qualified, it indicates that the self - calibration is successful. If there are unqualified items, it is necessary to check the operation steps, the connection of standard instruments, or the performance of the PR235 itself, and re - perform the self - calibration.

After the self - calibration is successful, record all calibration data in detail, including the calibration date, time, ambient temperature, humidity, the model and calibration certificate number of the standard instrument used, the calibration points, the original display values of the PR235, the standard values, the adjusted values, and the verification results.

Save the calibration record in a safe place for future reference and traceability. Some PR235 models can store the calibration data in the device's internal memory, which can be exported if necessary.

Disconnect the connection between the PR235 and the standard instruments, and organize the tools and materials used.

Turn off the PR235 and the standard instruments.

Clean the PR235's interface and surface to keep it clean.

Label the PR235 with the calibration date and the next calibration due date to facilitate management.

Strictly abide by the operation procedures to avoid incorrect operations that may damage the PR235 or standard instruments.

The standard instruments used must have higher accuracy than the PR235, generally at least 3 - 5 times higher, to ensure the reliability of the calibration results.

On - site self - calibration cannot completely replace professional metrology institution calibration. It is recommended to send the PR235 to a qualified metrology institution for a comprehensive calibration regularly (such as once a year) to ensure its long - term accuracy.

If any abnormal situation is found during self - calibration, such as the PR235 displaying abnormally or the adjustment cannot meet the requirements, stop the self - calibration immediately and contact professional maintenance personnel for inspection.