When measuring alternating current (AC) power, it's often necessary to disconnect the circuit first before connecting the ammeter. However, this can be quite inconvenient in practice. In situations where a circuit like a distribution line cannot be disconnected, an ammeter equipped with a clamp-on current transformer is typically used. A clamp ammeter is a portable tool that allows you to measure AC current directly without having to interrupt the circuit. This makes it highly convenient for electrical maintenance tasks. One of the greatest advantages of this method is that it enables the measurement of large currents without turning off the circuit under test.
Here’s how to properly use a clamp ammeter:
A clamp ammeter is a portable device designed to measure the current in a circuit without cutting off the power supply. It operates based on the principle of current transformers. When using a clamp meter, ensure that the current of the circuit under test does not exceed the meter's rated capacity. Avoid switching the measurement range while the wire is still clamped, as this could lead to dangerously high voltages in the current transformer, potentially causing personal injury or damaging the meter. For accurate readings, place the wire in the center of the jaws and make sure the jaws are securely closed. If the jaws aren't tightly shut, the magnetic resistance of the core will increase, leading to core overheating and a squealing noise. During the measurement process, operators should maintain a safe distance from live parts, especially when reading the display, to avoid coming too close to energized components, which could result in electric shock.
According to the regulations outlined in GB 26860-2011 "Electrical Safety Work Procedures for Electric Power Plants and Substations," when using a clamp ammeter, it's important to pay attention to the voltage rating of the meter. Insulated gloves should be worn when operating from an insulated surface, and care should be taken not to touch any other equipment to prevent short circuits or ground faults. Before measuring the current of low-voltage fuses or horizontally arranged low-voltage busbars, each phase should be isolated using insulating materials. When checking the readings, always keep a safe distance between your head and any live parts.
Top Ten Brands of Clamp Meters:
1. Youlide
2. Fluke
3. VICTOR
4. Xin Ling
5. Huayi
6. HIOKI
7. Agilent
8. ATTEN
9. Lei Yi
10. Baogong
Which Brand of Clamp Meter is Easiest to Use?
There are numerous brands of clamp meters available in the market, so which one is best? Based on user experiences, there are primarily two types: those distributed by foreign brands and domestically produced ones. The quality and precision of the latter can vary significantly. Prices on platforms like Taobao can serve as a reference.
Recommendation: I’ve personally used the Fluke KLUKE digital clamp meter, which is an imported product known for its reliability.
Methods and Diagrams for Testing Clamp Meters:
[Insert images showing clamp meter measurements for AC/DC current, voltage, and surge current]
Steps and Methods for Using the DT266 Clamp Meter:
The clamp meter mainly consists of a current transformer coil and a multimeter. The induced current from the transformer coil is read by the multimeter.
Taking the DT266 clamp meter as an example, here’s how it’s used:
1. AC Current Measurement:
- Set the switch to the ACA1000A range.
- Keep the switch relaxed.
- Press the trigger to open the jaws and clamp a single wire. Clamping multiple wires will render the measurement invalid.
- Read the value. If the reading is below 200A, switch the dial to the ACA200A range to enhance accuracy. In low-light conditions, press the hold button to illuminate the area for easier reading.
2. AC and DC Voltage Measurement:
- For DC voltage, set the switch to the ACA200A range. For AC voltage, set it to the ACV750V range.
- Keep the switch relaxed.
- Connect the red probe to the “V/Ω†terminal and the black probe to the “COM†terminal.
- Connect the probes in parallel with the line under test.
3. Resistance Measurement:
- Set the switch to the appropriate resistance range.
- Keep the switch relaxed.
- Connect the red probe to the “V/Ω†terminal and the black probe to the “COM†terminal.
- Connect the probes across the resistor being measured. If measuring line resistance, disconnect the line from the power source and discharge any capacitors attached to the resistor.
4. Continuity Test:
- Set the switch to the 200n range.
- Connect the red and black probes to the “V/Ω†and “COM†terminals, respectively.
- If the resistance between the probes is less than (50 ± 25) Ω, the internal buzzer will sound.
5. High Resistance Measurement:
- Set the switch to “EXTERNALUNIT†at either the 20MΩ or 2000MΩ range.
- The displayed value may be unstable initially.
- Insert the test accessory leads into the three input jacks of the clamp meter.
- Set the clamp meter switch and test accessory range switch to the 2000MΩ position.
- Connect the test accessory input terminals to the measured resistance.
- Turn on the test accessory power and press the “PUSH†button. The indicator light will come on, and the display will show the measured value. If the reading is less than 19MΩ, the clamp meter test accessory range should be set to 20MΩ for greater accuracy.
Things to Remember When Using a Clamp Meter:
Choose the right range; do not use a small range for large current measurements. If the current is small, wrap the current-carrying wire around the jaws several times, but divide the reading by the number of coils to get the actual current value. After completing the measurement, set the selector switch to the maximum range position (or leave it open) for safe future use. Do not change the range during measurement. Ensure the circuit voltage is lower than the clamp meter's rated value. Clamp current meters should not be used to measure high-voltage circuits, as this could lead to accidents or electric shocks.
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