Working principle and classification of clamp watches
A clamp ammeter, also known as a clamp ammeter, is an instrument that combines a current transformer and an ammeter. Its working principle is the same as measuring current with a current transformer. The working part mainly consists of an electromagnetic ammeter and a through core current transformer. The iron core of the through core current transformer is made into a movable opening and formed into a clamp shape, hence the name clamp ammeter. It is a portable instrument that can directly measure the AC current of a circuit without disconnecting the circuit. It is very convenient to use in electrical maintenance and is widely used.
Working principle of clamp watch
The working principle of a clamp type meter is the same as that of a transformer. The primary coil is a wire that passes through a clamp type iron core, equivalent to the primary coil of a 1-turn transformer, which is a step-up transformer. The secondary coil and the ammeter used for measurement form the secondary circuit. When there is alternating current passing through the wire, it is this turn of coil that generates an alternating magnetic field, causing induced current in the secondary circuit. The magnitude of the current and the proportion of the primary current are equivalent to the inverse ratio of the turns of the primary and secondary coils. A clamp type ammeter is used to measure large currents. If the current is not high enough, the number of turns of a wire passing through the clamp type ammeter can be increased, and the measured current can be divided by the number of turns. The secondary winding of the through core current transformer of the clamp type ammeter is wound around the iron core and connected to the AC ammeter. Its primary winding is the measured wire passing through the center of the transformer. The knob is actually a range selection switch, and the function of the wrench is to open and close the movable part of the core of the through core transformer, in order to clamp it onto the measured wire. When measuring current, press the wrench, open the clamp, and place the measured current carrying wire in the middle of the through core current transformer. When there is alternating current passing through the measured wire, the magnetic flux of the alternating current induces a current in the secondary winding of the transformer. This current passes through the coil of the electromagnetic ammeter, causing the pointer to deflect, and indicating the measured current value on the dial scale.
Pincer Table Classification
According to its structure and purpose, it can be divided into two types: transformer type and electromagnetic type. The commonly used type is a transformer clamp ammeter, which consists of a current transformer and a rectifier instrument. It can only measure AC current. The deflection of the movable part of an electromagnetic instrument is independent of the polarity of the current, so it can be used for both AC and DC purposes.
Features of clamp shaped watch
The clamp meter can be changed to different ranges by shifting the gears of the switch. However, it is not allowed to operate with power when shifting gears. The accuracy of clamp shaped watches is generally not high, usually ranging from 2.5 to 5 levels. For ease of use, there are also conversion switches with different ranges in the meter for measuring different levels of current and voltage. The clamp meter was originally used to measure AC current, but now it also has functions such as measuring AC and DC voltage, current, capacitance, diode, transistor, resistance, temperature, frequency, and so on.
How to use a clamp watch
(1) Mechanical zero adjustment is required before measurement
(2) Select the appropriate range, first select the large range, then select the small range or estimate the nameplate value.
(3) When using the minimum range measurement and the reading is not significant, the measured wire can be wound several turns, and the number of turns should be based on the number of turns in the center of the clamp, then the reading=the indicated value × Range/full deviation × Number of turns
(4) After measuring, place the transfer switch at the maximum range.
(5) When measuring, the measured wire should be placed in the center of the clamp and the clamp should be tightly closed to reduce errors.
