Working Principles and Calibration Methods of Multimeters
Voltage measurement:
A multimeter compares the measured voltage with a standard voltage (such as a 1.5V or 9V battery) through an internal circuit to measure the voltage value.
For AC voltage, a multimeter uses a rectifier circuit to convert AC to DC and then measures it.
Current measurement:
A multimeter measures current by connecting a precise resistor (called a shunt resistor) in series.
When current flows through this resistor, a voltage drop is generated. A multimeter measures this voltage drop and calculates the current value based on Ohm's law.
Resistance measurement:
A multimeter uses an internal power supply to apply voltage to the measured resistor and measure the current flowing through the resistor.
According to Ohm's law (V=IR), a multimeter can calculate the resistance value.
Diode and transistor testing:
A multimeter can measure the forward and reverse voltage drops of diodes, as well as the amplification factor of transistors.
Other functions:
Some multimeters also have functions such as measuring capacitance, frequency, temperature, etc.
Method for calibrating a multimeter
Preparation standard reference:
Use standard resistors, voltage sources, or current sources with known accurate values as references.
Calibration resistor:
Set the multimeter to resistance measurement mode and connect the probe to a standard resistor with a known resistance value.
Adjust the calibration knob of the multimeter until the displayed reading matches the actual value of the standard resistor.
Calibration voltage:
Set the multimeter to DC voltage measurement mode and connect the probe to a standard voltage source with a known voltage value.
Adjust the calibration knob of the multimeter until the displayed reading matches the actual value of the standard voltage.
Calibration current:
Set the multimeter to current measurement mode and connect the probe to a standard current source with a known current value.
Adjust the calibration knob of the multimeter until the displayed reading matches the actual value of the standard current.
Repeat calibration:
For multi range multimeters, it may be necessary to repeat the calibration process on different ranges.
Use calibration certificate:
If possible, use calibration certificates to verify the accuracy of the calibration process.
Regular calibration:
Regularly calibrate the multimeter to ensure the accuracy of measurement results.
