The purpose of this procedure is to provide instruction for the calibration of digital multimeters (DMM). Scope
All multimeters (multi-range instruments used to measure voltage, current, and resistance) are to be verified in calibration no less than once per year. Procedure
Preliminary Instructions and Notes
1. Read this entire procedure before beginning the calibration. 2. Calibration shall be performed in an environment that conforms to Manufacturer Specifications. 3. The digital multimeter will hereafter be referred to as the Instrument Under Test (IUT). 4. Verify that the IUT is clean.
5. Visually examine the IUT for any condition that could cause errors in the calibration. 6. If any of the requirements cannot be met, refer to the applicable manufacturer manual. 7. If a malfunction occurs or a defect is observed while calibration is in progress, the calibration shall be discontinued and necessary corrective action taken; if corrective action affects a measurement function previously calibrated, the function shall be recalibrated before the remainder of the procedure implemented. Reference Material
Applicable Manufacturers Manual or Brochures.
The specifications of the IUT are determined by the applicable manufacturer's documentation. If the manufacturer's documentation is not available, then the specifications identified in this procedure are used. Equipment Required
The Standards listed below should be selected on the basis of their higher accuracy level when compared to the unit under test. Equivalent Standards must be equal to or better than the Minimum-Use-Specification. Minimum-Use-Specifications for Standards listed are 1/4 the accuracy required by the IUT. * Rotek Model 2500 Calibrator or equivalent
* Diode Test Fixture
* Test Leads
* Continuity Test Fixture
* Capacitance Test Fixture
Turn all power on (calibrator and the unit to be calibrated). Allow the instruments to stabilize for approximately 5 minutes. Conduct the tests in an ambient temperature of 25 ± 5C and a relative humidity of less than 80%. Note: If the IUT has an automatic ranging feature, then the function being checked (i.e. voltage, current, or resistance) must be verified in the variable range mode as well. Battery Replacement
Replace the battery in the IUT and make sure the battery contacts are not dirty. Detailed Procedure
Display and Switch Test
Turn the IUT on and verify that all LCD segments are working and not dim. Verify that the selector switch(s) is/are working properly. Make sure the Low Battery indicator is not showing. Resistance Check
Connect the calibrator between the V/ohm and common input terminals of the IUT. Use the following chart to verify the resistance values. Step | Range | Input | Display |
1 | 200 ohm | Short | 00.0 to 00.5 |
2 | 2 k ohm | Short | 0.000 to 0.001 |
3 | 2 k ohm | 1 k ohm | .998 to 1.002 |
4 | 20 k ohm | 10 k ohm | 9,98 to 10.02 |
5 | 200 k ohm | 100 k ohm | 99.8 to 100.2 |
6 | 2000 k ohm | 1 M ohm | 998 to 1002 |
7 | 2000 M ohm | Open | 0.10 to 00.0 |
1. Select the continuity check function on the calibrator. 2. Connect the test leads to the V/ohm and common terminals of the IUT. 3. Momentarily short the test leads together and observe that the tone sounds. 4. Connect the test leads to the continuity test fixture between the 100 ohm test points. No tone should be heard indicating non-terminating connection. 5. Connect the test leads to the continuity test fixture between the 50 ohm set up. The test tone should indicate continuity between the test points. DC Voltage Test
1. Use the calibrator to supply the correct DC voltage listed below. 2. Set the calibrator for a zero volt input.
3. Connect the calibrator output to the V/ohm and common input terminals of the IUT....