Table of Contents
The objective of this procedure is providing instructions for calibrating digital multimeters (DMM).
Scope
All multimeters (multi-range instruments that measure voltage, current, & resistance) must be calibrated at least once a year.
Procedure
Preliminary Instructions
- Before you start the calibration, read this complete protocol.
- Calibration must be performed in an atmosphere that meets Manufacturer specifications.
- The digital multimeter will now be identified as the Instrument Under Test (IUT).
- Ensure that the IUT is cleaned.
- Visually inspect the IUT for any possible faults in calibration.
- If any of the specifications cannot be met, consult the relevant manufacturer documentation.
- If a malfunction or defect is discovered while calibration is being performed, the calibration must be stopped and the appropriate remedial measure taken; if the corrective action affects a previously calibrated measurement function, the function must be recalibrated before the remainder of the procedure is carried out.
Reference Material
Manufacturer’s manual (or) brochures.
Specifications
The IUT specs are specified by the corresponding manufacturer’s documentation.
Equipment Required
The Standards indicated below should be chosen based on a greater accuracy level as compared to unit being tested.
Equivalent Standards should be equal to or higher than the minimum-use-specification.
The mentioned standards have a minimum-use specification of 1/4 the precision needed by the IUT.
- Rotek Model 2500 Calibrator
- Diode Test Fixture
- Test Leads
- Continuity Test Fixture
- Capacitance Test Fixture.
- Thermometer
- Hydrometer
Set-Up
Turn on all power (calibrator and calibration unit). Permit the instruments to steady for around 5 minutes.
Tests should be conducted at a temperature of 25 ± 5 degrees Celsius and relative humidity of below 80 percent.
Note:
If the IUT supports automated ranging, the function being checked (voltage, current, (or) resistance) also needs to be confirmed in variable range mode.
Battery Replacement
Replace the battery in IUT, and check to ensure the battery contacts are clean.
Detailed Procedure
Display & Switch Test
- Turn on the IUT and ensure that all LCD sections are operational and not dimmed.
- Check that the selection switch(s) is/are functioning properly.
- Check that the Low Battery indication is not visible.
Resistance Check
- Connect the calibrator to the V/ohm & common input terminals of IUT.
- Use the chart below to confirm the resistance values.
| Step | Range | Input | Display |
| 1 | 200 Ω | Short | 00.0 to 00.5 |
| 2 | 2 KΩ | Short | 0.000 to 0.001 |
| 3 | 2 kΩ | 1 kΩ | .998 to 1.002 |
| 4 | 20 kΩ | 10 kΩ | 9,98 to 10.02 |
| 5 | 200 kΩ | 100 kΩ | 99.8 to 100.2 |
| 6 | 2000 kΩ | 1 MΩ | 998 to 1002 |
| 7 | 2000 MΩ | Open | 0.10 to 00.0 |
Continuity Test
- Use the calibrator’s continuity check feature.
- Attaching the test leads to V/ohm & common terminals on the IUT.
- Shorten the test leads and listen for the tone.
- Attach the test leads to continuity test equipment at the 100Ω test locations.
- No tone should be heard to indicate a non-terminating connection.
- Connect test leads to continuity test equipment in the 50 Ω configuration.
- The test tone should convey continuity between test points.
DC Voltage Test
- Using the calibrator, deliver the appropriate DC voltage specified below.
- Configure the calibrator to a zero-volt input.
- Connect calibrator output to the V/Ω & common input terminals on the IUT.
- Connect the ground, common, and low sides of the Rotek 2500 to the common on IUT.
- Refer to the table below to pick IUT voltage range & configure the calibrator output to match the IUT input voltage.
- Test the display using the chart below and ensure that it falls within the boundaries specified.
| Step | Range | Input | Display |
| 1 | 200 mV | 190mV | 189.7 to 190.3 |
| 2 | 200 mV | – 190mV | -189.7 to -190.3 |
| 3 | 2 V | 0.0 V | -0.001 to 0.001 |
| 4 | 2 V | 1.9 V | 1.897 to 1.903 |
| 5 | 20 V | 19 V | 18.97 to 19.03 |
| 6 | 200 V | 100 V | 99.84 to 100.16 |
| 7 | 1000 V | 400 V | 399.3 to 400.6 |
AC Voltage Test
In the test that follows, supply the appropriate AC voltage using the calibrator:
- Set 60 Hz on the calibrator.
- Attach the calibrator outputs to the IUT’s common input terminal and V/ohm terminals. Join the calibrator’s low, ground, and common sides to the IUT’s common.
- Choose the IUT voltage range from step 1 & set calibrator output to matching IUT input voltage using the table below as a point of reference. Check to make sure the displayed reading is within set bounds.
| Step | Range | Input | Display |
| 1 | 200 mV | 100 mV | 99.0 to 101.0 |
| 2 | 2 V | 1 V | 0.990 to 1.010 |
| 3 | 20 V | 10 V | 9.9 |
| 4 | 200 V | 100 V | 99.0 to 100.1 |
| 5 | 750 V | 400 V | 294 to 406 |
DC Current Test
Provide the appropriate DC current shown in the following table using the calibrator:
- Set the calibrator’s output to zero milliamperes.
- Attach the calibrator’s output to the IUT’s common input terminal and lowest current terminal, which are normally connected at 200 mA respectively.
Note:
Don’t use more current than the meter’s maximum rating. Check merely for values that the meter can read.
- Choose IUT current range & set calibration output to supply the corresponding IUT input current by consulting the table below. Check to make sure the displayed reading is within set bounds.
| Step | Range | Input | Display |
| 1 | 200 A | 190 A | 189.7 to 192.3 |
| 2 | 2 mA | 1.9 mA | 1.897 to 1.923 |
| 3 | 20 mA | 19 mA | 18.97 to 19.23 |
| 4 | 200 mA | 190 mA | 189.7 to 192.3 |
- Turn off the calibrator and connect the common input line while adjusting the IUT’s current terminal to the maximum value, which is usually 10 A.
- To confirm that the meter is operating within the given parameters, use the following table.
| Step | Range | Input | Display |
| 1 | 10 A | 1 A | 0.98 to 1.02 |
| 2 | 10 A | 5 A | 4.90 to 5.10 |
| 3 | 10 A | 9 A | 8.82 to 9.18 |
AC Current Test
As indicated in the table below, deliver the appropriate AC current using the calibrator:
- To confirm that the meter is operating within the given parameters, use the following table.
- Set the calibrator’s output to zero milliamperes.
- Attach the calibrator’s output to both the unit being tested common terminal and low current input line (usually 200 mA).
| Step | Range | Input | Display |
| 1 | 200 mA | 190 mA | 18.27 to 19.28 |
| 2 | 2 mA | 1.9 mA | 1.872 to 1.928 |
| 3 | 20 mA | 19 mA | 18.72 to 19.28 |
| 4 | 200 mA | 190 mA | 187.2 to 192.8 |
Note:
Don’t use more current than the meter’s maximum rating. Check just for values that the meter can read.
- Choose the IUT current range & adjust the calibrator output to supply the appropriate IUT input current by consulting the table below.
- Check to make sure the displayed reading is within set bounds.
- Turn off the calibrator and connect the common input line while adjusting the IUT’s current terminal to the maximum value, which is usually 10 A.
- To confirm that the meter is operating within the given parameters, use the following table.
| Step | Range | Input | Display |
| 1 | 10 A | 1 A | 0.97 to 1.03 |
| 2 | 10 A | 5 A | 4.87 to 5.13 |
| 3 | 10 A | 9 A | 8.77 to 9.23 |
Logic Test
- Try using this process to see if the logic function indicates the right condition.
- Place the test leads into the common terminals and V/ohm and set IUT to logic test mode.
- To ensure that the meter displays a low logic state, short the leads together.
- Affirm that the calibrator is set to 0.400 VDC & attach the meter to any output terminals. Determine whether the meter reads low logic.
- To ensure that the IUT displays a high logic state, set the calibrator to 3.500 VDC.
Frequency Test
- Utilize a function generator and an oscilloscope to measure the AC sine waves.
- The oscilloscope can be used to set frequencies based on the following table. Initially set the function generator to output 10 VAC.
- As well as ground and the function generator’s output, connect IUT leads to the device’s common, V/ohm, and other terminals.
- Make that the findings from the table are accurately displayed by the meter.
| Step | Range | Input | Display |
| 1 | Hz | 60 Hz /10 V | 59.4 to 60.6 Ω |
| 2 | Hz | 1 kHz / 10 V | .990 to 1.010 kΩ |
| 3 | Hz | 1 MHz / 10 V | .990 to 1.010 M Ω |
Capacitance Test
- Before inserting the test leads into the common test terminals and V/ohm, set IUT to measure capacitance.
- Determine the IUT’s ability by connecting the meter to the capacitance test fixture & using the table below:
| Step | Range | Input | Display |
| 1 | Capacitance | 10 μF | 9.85 to 10.15 |
| 2 | Capacitance | 1 μF | .985 to 1.015 |
| 3 | Capacitance | 100 μF | 98.5 to 101.5 |
Diode Test
- Attach test leads to V/ohm and common terminals, and set IUT to the diode check function.
- To check the diode test operation, connect test leads to diode test fixture & follow the instructions in the following table:
| Step | Range | Setup | Polarity | Display | Tone |
| 1 | Check Diode | Short | Not Available | .000 to .001 | Yes |
| 2 | Check Diode | Si | Forward | .800 to .600 | Yes |
| 3 | Check Diode | Si | Reverse | 1 | No |
| 4 | Check Diode | Ge | Forward | .300 to .500 | Yes |
| 5 | Check Diode | Ge | Reverse | 1 | No |
- Some meters may not have a tone feature.
