Current measurement is not the same as measuring other quantities with a DMM. The direct current measurement method is to connect the digital multimeter directly to the circuit under test, so that the current of the circuit under test flows directly into the internal circuit of the multimeter. The indirect measurement method does not require opening the circuit and stringing the multimeter to the circuit under test. The indirect method uses a current clamp.
direct measurement
1. Turn off the circuit power
2. Disconnect or desolder the circuit in order to string the meter into the circuit
3. Select the corresponding AC (A~), DC (A--) gear
4. Insert the black test lead into the COM socket and the red test lead into the 10A jack (10A) or the 300mA jack (300mA). The choice of which jack is mainly based on the possible measurements.
5. Connect the test leads to the disconnected circuit part in series.
6. Turn on the circuit power
7. Observe the readings and note the units.
Note: When measuring DC, if the test probe is reversely connected, "-" will appear.
input protection
A common mistake is to put the test leads in the current jacks while trying to test the voltage. Small value resistors in DMMs can short-circuit the voltage source. A large current flows through the digital multimeter. If the multimeter is not adequately protected, it will not only damage the meter and circuit, but also harm the operator. In the case of high-voltage circuits (480 volts or higher), there is a greater danger.
Therefore, the digital multimeter should have a large enough current input protection fuse. Meters without current input fuses cannot be used in high energy circuits (>240V ac). Using a digital multimeter with a fuse, the fuse should have a large enough capacity.
amount to remove high-energy faults. The voltage rating of the fuse should be greater than the maximum voltage you expect. For example, one of the multimeters
The 20A, 250V fuse cannot protect the multimeter when measuring the 480V circuit. A 20A, 600V fuse can play a protective role when the multimeter measures a 480V circuit.
Current test
Sometimes, the current value you want to measure exceeds the range of the digital multimeter or the field conditions do not allow you to open the circuit to measure the current. Current clamps are very handy when testing at high currents (usually greater than 2A) without the need for high precision. A current clamp measures the current around the wire and converts it to a value that a digital meter can handle.
There are two basic current probes: the current transformer type, which is used for AC measurements only. Hall-effect probes for measuring AC or DC current.
Current converter type. 1 mA is generally used to represent 1 amp. A current value of 100 amps becomes 100 mA, which can be safely measured with a DMM. Connect the wires to the "mA" and "Com" jacks, and turn the function selector knob to the AC mA position.
Hall effect probe. Use 1 millivolt to represent an AC or DC value of 1 amp. For example, 100 amps of AC current is converted to 100 millivolts of AC voltage. Connect test leads to the "V" and "Com" jacks. Rotate the function selection knob to "V" or "mV". At this time, the multimeter uses 1 millivolt to represent 1 amp of current.
When disconnecting or desoldering a circuit for a current measurement, the power to the circuit to be tested must be disconnected. Small currents can also be dangerous.
Do not test voltages with test leads inserted in the current holes. It may cause damage to the watch or endanger personal safety.
Inverter-type current probes, like the Fluke 80i-400. The DMM uses a 1mA display to represent the actual 1A signal.
Fluke I-1010 Hall-Effect Probe can measure very high AC or DC currents. It converts current into voltage signal.
A voltage display of 1mV represents an actual current of 1A.
