Clamp Leakage Meter and Clamp Meter
1. Current clamp meter
Clamp-on ammeter is called clamp-on meter for short. It is mainly used to directly measure the current on the low-voltage line (without disconnecting the wire). It is quite convenient to use and is a necessary measuring instrument for motor repair. At present, there are mainly two types: pointer type and digital type.
Pay attention to the following when using a clamp ammeter:
(1) Select gear and range. Before measuring, the gear and range should be selected first. If you want to measure voltage, you should turn the switch to the "V" block; if you want to measure current, you should estimate the approximate value of the measured current to select the appropriate range. If it is difficult to estimate, you should use a large range first, and then gradually adjust to a suitable small range. Meter will be damaged when measuring large current with small range.
(2) Adjust the zero position of the pointer and test. After selecting the gear and range of the clamp meter, you should observe whether the pointer (pointer clamp meter) is at zero or whether the number is zero (digital clamp meter). If the indication value of the clamp meter is not zero when it is not measured, it should be adjusted, otherwise it will affect the accuracy of the measurement. Before formal measurement, it should be tested on a wire with known current value to verify its quality.
(3) Pay attention to the measurement method. When measuring AC current, the position of the measured current-carrying insulated wire (if it is a bare wire, it should be wrapped and insulated first) should be in the center of the jaws to avoid errors. The jaws should be tightly fitted. If there is any noise or the pointer vibrates, it is mostly caused by foreign objects at the jaws. At this time, the foreign objects should be removed and the measurement should be repeated.
When measuring current on a low-voltage circuit, special attention should be paid to keeping a safe distance between its head and live parts. In addition, when the clamp-on ammeter is too close to the electrical appliance (such as a motor), the measurement data is often inaccurate; when measuring a current less than 5 A, in order to make the measurement accurate, the current-carrying wire can be wound on the jaw for a few more times when conditions permit. Turns, the measured reading divided by the number of turns of the wire, is the value of the actual current.
When measuring voltage, in addition to shifting the gear to the "V" position, according to the magnitude of the measured voltage, first insert the test leads into the corresponding jacks, and then touch the two test leads to the measured point at the same time, and the reading on the dial will That is, the voltage value of the two points to be measured.
(4) Correct reading. There are two scale lines, red and black, on the dial of the clamp meter. The red scale line is the voltage scale line, which is used for reading when measuring voltage; the black scale line is the current scale line, which is used for reading when measuring current. The actual measured value should be the product of the indicated value of the pointer and the multiplier of the range switch. For example, if the indication value of the pointer is 150 A (the scale value of the dial is 0-300 A), if the range switches are respectively located at 30 A, 300 A, and 3 000 A, the actual current values are 15 A, 150 A, and 1 500 A respectively. a.
(5) Pay attention to safety. It is strictly forbidden to change the range gear during the measurement process. Because the clamp core transformer is a current transformer with many secondary turns, it is equivalent to a secondary open circuit during conversion, which will induce a high voltage, which may break down the insulation, causing instrument damage and personal electric shock accidents. After the measurement, loosen the jaws of the current clamp meter, slowly take out the wire, and pay attention to set the range switch to the highest current or voltage position, so as to prevent the wrong range from being carelessly selected in the next use. cause the watch hands to bend or cause other accidents. In addition, in thunderstorm weather, in order to ensure safety, it is forbidden to measure with clamp ammeter outdoors.
2. Clamp leakage current meter
Clamp leakage current meter is a new type of AC current testing instrument introduced in recent years. Its appearance is similar to ordinary clamp current meter, but it is actually a high-sensitivity current transformer. The clamp leakage current meter can generally not only measure the magnitude of the low-voltage leakage current, but also measure the active component and the value of the insulation resistance in the leakage current. When measuring the leakage current of electrical appliances or wires in operation, the live wire and the neutral wire (referring to single-phase AC appliances) or three live wires (referring to three-phase AC appliances) should be clamped together in the clamp leakage current meter, which is it The biggest difference from ordinary clamp ammeters.
