Calibration method of loop resistance tester and DC resistance quick tester

1. Appearance inspection

The appearance of the loop resistance tester and DC resistance quick tester should be intact, the various adjustment knobs and key switches should be flexible and reliable, and the digital display should not overlap or not display some strokes. There should be a dedicated grounding terminal and an obvious grounding mark.

The nameplates on the loop resistance tester and DC resistance quick tester should clearly indicate: product name, manufacturer, model, factory number, date of manufacture and accuracy level. The current terminal, voltage terminal, various adjustment knobs, and key switches should be marked with words or symbols indicating their functions, and their meanings should be accurate.

2. Insulation resistance detection

Use a 500v insulation resistance meter to measure the insulation resistance between the input terminal of the tested loop resistance tester and DC resistance quick tester and the chassis. It is required that the insulation resistance between the power input terminal and the chassis should not be less than 20mω.

3. Dielectric strength

Apply 1500v power frequency voltage between the power input terminal of the tested instrument and the casing for 1 minute. It is required to pass the power frequency withstand voltage test without breakdown or arcing.

4. Basic error testing

The standard resistance method is generally used to calibrate the basic error. Other calibration methods are allowed under the condition that the total uncertainty allowed by the calibration is not exceeded, but it must be approved by the higher-level metrology department. However, when the calibration data is in dispute, the standard resistance method shall prevail. The wiring diagram during calibration is shown in Figure 1.

Figure 1: Standard resistance method calibration wiring diagram

Use special wires to connect the measurement current terminals and voltage terminals of the tested loop resistance tester and DC resistance quick tester with the current terminals and voltage terminals of the selected standard resistor. Record the resistance value of the standard resistor and the indicated value of the tested tester.

The calibration points of the loop resistance tester and DC resistance fast tester are 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100 of the resistance range of the tested tester. %, a total of 10 points. When calibrating the basic error of a multi-range tester, its wiring for all ranges should be calibrated.

5. Short-term stability test

The short-term stability test is performed at the upper limit calibration point of the minimum range of the loop resistance tester and DC resistance quick tester. During the 5 minutes of continuous operation of the loop resistance tester and DC resistance fast tester, observe and record the indicated value of the tester. The change in error should not be greater than 1/3 of the operating error corresponding to its accuracy level.

6. Ripple test

When testing the current ripple of the loop resistance tester and DC resistance quick tester, you can use a low-resistance reactor to convert the current signal into a voltage signal before testing. The ripple of the tester's output DC current is caused by The error should be less than 1/5 of the operating error corresponding to the accuracy level of the tester.