Clamp ammeter and clamp leakage ammeter
1. Clamp ammeter
Clamp ammeter, referred to as clamp current meter, is mainly used to directly measure the current on low-voltage lines (without disconnecting the wire). It is very easy to use and is a necessary measuring instrument for motor repair. It consists of an openable current transformer and a meter. At present, there are mainly two types: pointer type and digital type.
When using a clamp ammeter, please pay attention to the following matters:
(1) Select the gear and range. Before measuring, you should first select the gear and range. If you want to measure voltage, you should set the switch to the "V" position; if you want to measure current, you should estimate the approximate value of the current being measured to select the appropriate range. If it is difficult to estimate, use the large range first, and then gradually adjust to the appropriate small range. Measuring large currents with a small range will damage the instrument.
(2) Adjust the pointer zero position and test. After selecting the gear and range of the clamp flow meter, you should observe whether the pointer (pointer type clamp flow meter) is at zero or whether the number is zero (digital clamp flow meter). If the indicated value of the flow clamp meter is not zero when not measuring, it should be adjusted, otherwise it will affect the accuracy of the measurement. Before formal measurement, you should test it on a wire with a known current value to verify its quality.
(3) Pay attention to the measurement method. When measuring AC current, the position of the current-carrying insulated wire to be measured (if it is a bare wire, it must be wrapped with insulation first) should be in the center of the jaws to avoid errors. The jaws should fit tightly. If there is any noise or the pointer shakes, it is mostly caused by foreign matter in the jaws. At this time, the foreign matter should be removed and the measurement re-measured.
When measuring current on a low-voltage circuit, special attention should be paid to keeping a safe distance between the head and the live parts. In addition, when the clamp ammeter is too close to the electrical appliance (such as a motor), the measurement data is often inaccurate; when measuring currents less than 5 A, in order to make the measurement accurate, if conditions permit, the current-carrying wire can be wound around the jaws a few more times. Turns, the measured reading divided by the number of turns of the wire is the actual current value.
When measuring voltage, in addition to setting the gear to the "V" position, first insert the test leads into the corresponding jacks according to the size of the voltage being measured, and then touch the two test leads to the measured point at the same time. The dial reading That is the voltage value of the two measured points.
(4) Correct reading. There are red and black scale lines on the dial of the clamp flow meter. The red scale line is the voltage scale line, used for reading when measuring voltage; the black scale line is the current scale line, used for reading when measuring current. The actual measured value should be the product of the pointer indication value and the range switch magnification. For example, if the pointer indicates 150 A (the dial scale value is 0 to 300 A) and the range switches are respectively 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 prohibited to change the range gear during the measurement process. Because the clamp core transformer is a current transformer with a large number of secondary turns, it is equivalent to a secondary open circuit during conversion, which will induce a very high voltage and may cause insulation breakdown, causing instrument damage and personal electric shock. After the measurement is completed, the jaws of the current clamp meter should be loosened, the wires should be slowly taken out, and the range switch should be set to the highest current or voltage position to prevent carelessness in not selecting the appropriate range the next time it is used. Cause the watch needle to bend or cause other accidents. In addition, during thunderstorms, to ensure safety, it is prohibited to measure with a clamp ammeter outdoors.
