Clamp type ammeter and clamp type leakage ammeter
1. Clamp type ammeter
The clamp current meter, also known as the clamp current meter, is mainly used to directly measure (without disconnecting wires) the current on low-voltage lines. It is quite convenient to use and is an essential measuring instrument for motor repair. It is composed of a current transformer and a meter head that can be opened. At present, there are mainly two types: pointer type and digital type.
When using a clamp type ammeter, the following precautions should be taken:
(1) Select the gear and range. Before measuring, the gear and range should be selected first. If measuring voltage, the switch should be turned to the "V" position; If you want to measure current, you should estimate the approximate value of the measured current to choose the appropriate range. If it is difficult to estimate, a large range should be used first, and then gradually adjusted to a suitable small range. Measuring large current with a small range can damage the instrument.
(2) Adjust the pointer zero position and test. After selecting the gear and range of the clamp current meter, it is necessary to observe whether the pointer (pointer clamp current meter) is in the zero position or whether the number is zero (digital clamp current meter). If the indicated value of the clamp flow 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, a test should be conducted 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 tested current carrying insulated wire (if it is a bare wire, insulation should be wrapped first) should be in the center of the clamp to avoid errors. The jaws should be closely matched. If there is noise or pointer shaking, it is often caused by foreign objects at the jaws. At this time, the foreign objects should be removed and re measured.
When measuring current on a low-voltage circuit, special attention should be paid to maintaining a safe distance between its head and the live part. In addition, when the clamp ammeter is too close to the consumer (such as the motor), the measurement data is often inaccurate; When measuring a current below 5 A, in order to ensure accurate measurement, if conditions permit, the current carrying wire can be wound a few more turns on the clamp. 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, according to the magnitude of the measured voltage, first insert the probe into the corresponding socket, and then touch the measured point simultaneously with both probes. The dial reading is the voltage value of the two measured points.
(4) Correct reading. There are two scale lines on the dial of the clamp flow meter, red and black. 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 a value of 150 A (with a dial scale value of 0-300 A) and the range switch is located at 30 A, 300 A, and 3000 A, the actual current values are 15 A, 150 A, and 1500 A, respectively.
(5) Pay attention to safety. It is strictly prohibited to switch the range during the measurement process. Due to its clamp shaped iron core transformer being a current transformer with a large number of secondary turns, the conversion is equivalent to a secondary open circuit, which will induce a high voltage and may cause insulation breakdown, causing instrument damage and personal electric shock accidents. After the measurement is completed, the clamp of the clamp current meter should be loosened, the wire should be slowly removed, and attention should be paid to setting the range switch to the highest current or voltage position, in order to prevent the meter needle from bending or causing other accidents due to carelessness in selecting a suitable range during the next use. In addition, in thunderstorm weather, to ensure safety, it is prohibited to use a clamp type ammeter for measurement outdoors.
2. Clamp type leakage current meter
The clamp leakage current meter is a new type of AC current testing instrument introduced in recent years. Its appearance is similar to that of an ordinary clamp current meter, but it is actually a high sensitivity current transformer. The clamp type leakage current meter can generally measure the magnitude of low-voltage leakage current, as well as the active component and insulation resistance value in the leakage current. When measuring the leakage current of running electrical appliances or wires, the live wire should be clamped together with the zero wire (referring to single alternating current appliances) or three live wires (referring to three-phase alternating current appliances) in a clamp type leakage current meter. This is the biggest difference between it and a regular clamp type current meter. At present, the clamp leakage current meter produced by Kyoritsu can measure a leakage current of 4 mA and a working current of 1000 A. It also has the function of a regular clamp current meter and is available for selection.
