How to measure current with digital multimeter and usage of current gear
How to Measure Current with Digital Multimeter
Measuring current 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 method does not need to open the circuit and connect the multimeter to the circuit under test. The indirect method uses a current clamp.
First of all, the multimeter must have a gear for measuring current. Then, insert the test leads into the current measuring jack on the left, and then connect the multimeter to the line to be tested in series. If you don't know how much current there is, it is best to increase the gear, if it is not suitable, then lower it to avoid burning the meter.
①Insert the red test lead into the "μ, mA, ℃" or IOA jack, and the black test lead into the "COM" jack.
②Set the functional range switch to the μA￣=, mA￣ or A current measurement position. The default setting is DC current measurement. If AC measurement is required, press the SE-LECT blue key to select AC current measurement.
③ When measuring current, the test leads should be connected in series in the circuit under test, and the red test leads should be close to the positive side of the power supply, otherwise "-" will appear on the LCD display (the AC current test leads are not divided into positive and negative).
④ Read the measurement results from the LCD display, and the value measured by Uyou OE is the true effective value.
Measurement Notes:
① When measuring, use the correct jack, function gear and range. If the current cannot be estimated, start the test from a higher range;
② When testing high current, for safety reasons, each measurement time should be less than 10S, and the interval time should be greater than l5min;
③When the test lead is inserted into the current jack, do not connect the test lead to any circuit in parallel, otherwise the fuse or even the multimeter itself may be blown.
direct current 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~) and DC (A--) gears;
4. Insert the black test lead into the COM socket, and insert the red test lead into the 10 amp jack (10A) or 300 mA jack (300mA). The choice of that jack is mainly based on possible measurements;
5. Connect the test leads in series to the disconnected circuit part;
6. Turn on the power supply of the circuit; 7. Observe the reading and pay attention to the unit;
Note: When measuring DC, if the test probe is reversed, "—" will appear.
input protection
A common mistake is to place the test leads in the current jacks while attempting to test the voltage. A small value resistor in a DMM can cause a short circuit to the voltage source.
Large current flows through the digital multimeter. If the multimeter is not protected enough, it will not only damage the meter and circuit, but also injure the operator. If it is a high-voltage circuit (480 volts or higher), it will cause greater danger.
Therefore, the digital multimeter should have a large enough current input protection fuse. Meters without current input fuses cannot be used on high energy circuits (>240V ac). For digital multimeters that use fuses, the fuses should have a large enough capacity.
amount to remove high energy faults. The rated voltage of the fuse should be greater than the maximum voltage you expect. For example, a 20A, 250V fuse in a multimeter cannot protect it when the multimeter measures a 480V circuit. A 20A, 600V fuse can play a protective role when the multimeter measures a 480V circuit.
Current Test Accessories
Sometimes the current value to be measured exceeds the range of the digital multimeter or the field conditions do not allow to open the circuit to measure the current. When testing high current (usually greater than 2A) and does not require high precision, the current clamp will be very convenient. Current clamps are placed around the wires to measure the current and convert it to a value that a digital meter can handle.
There are two basic types of current probes: Current transformer types, which are used for AC measurements only. Hall-effect probes for measuring AC or DC current.
current converter type. Generally, 1 milliamp is used to represent 1 amp. A current value of 100 amps becomes 100 mA, which is safe to measure with a DMM. Connect the wires to the "mA" and "Com" jacks, and turn the function selector knob to AC mA.
Hall effect probes. Use 1 millivolt to represent an AC or DC value of 1 amp. For example, an AC current of 100 amps is converted to a voltage of 100 millivolts AC. Connect the test leads to the "V" and "Com" jacks. Turn the function selection knob to "V" or "mV". At this time, the multimeter uses 1 millivolt to represent 1 ampere.
When disconnecting or desoldering a circuit for current measurement, the power to the circuit under test must be disconnected. Small currents can also cause danger.
Do not test for voltage with the test leads inserted into the current holes. It may cause damage to the watch or endanger personal safety. A transducer type current probe, like the Fluke 80i-400. The digital multimeter uses the display of 1mA to represent the actual 1A signal. The Fluke I-1010 Hall effect probe can test very high AC or DC currents. It converts current into a voltage signal. A voltage display of 1mV represents an actual current of 1A.
