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What is an ammeter
An ammeter is an instrument used to measure current in AC and DC circuits. In the circuit diagram, the symbol of the ammeter is “circle A”. Current values are in “amps” or “A” as standard units.
Classification of ammeters
1. DC ammeters: Mainly use magnetoelectric or electric measurement mechanisms (see mechanical instructions Electric meter measuring mechanism), the basic measurement of these measuring mechanisms is current, which can be used to directly measure small currents.
2. AC ammeter: It can use electromagnetic system or electric system measurement mechanism. In order to make the magnetoelectric system measuring mechanism also used to measure alternating current, the alternating current can be converted into direct current by using devices such as rectifiers or thermocouples; Thermoelectric ammeter. In order to expand the range to measure large currents, the rectifier ammeter also uses a shunt; the electric ammeter is the same as the previous one; the electromagnetic ammeter is to thicken the coil wire and reduce the number of turns. For larger measured current values, it needs to be used with current transformers.
How to use the ammeter
1. Connect the meter: The ammeter must be connected in series in the circuit under test, so that the current flows in from the “+” terminal of the ammeter and flows out from the “-” terminal. When using an ammeter, its two terminals must not be directly connected to the two poles of the power supply, otherwise the ammeter will be burned out due to excessive current.
2. Select the range of the meter: The ammeter has three binding posts, as shown in the figure above, if the ammeter is connected to the “+” and “0.6” binding posts, its The range is 0.6A, and the group of values on the dial is read; if it is connected to the “+” and “3” terminals, the range is 3A, and the group of values on the dial is read. Before the experiment, if you do not know how to connect, you can first estimate the current value in the circuit. If the estimated current is less than 0.6A, the range should be selected. If the estimated current is greater than 0.6A but less than 3A, the range should be selected. If it is impossible to estimate, you can use the method of test touch (fix one terminal, and use another wire end of the circuit to quickly touch the terminal of the maximum range), and then select the appropriate range according to the deflection angle of the ammeter pointer.
3. Trial circuit: After the physical diagram is connected according to the circuit diagram, it must be tested. Carefully observe the deflection of the ammeter pointer during the test connection. If the pointer does not deflect, it means that the circuit is broken somewhere; if the pointer deflects in the opposite direction, it means that the positive and negative terminals of the meter are reversed; It means that the range is too small; if the deflection angle of the pointer is too small, it means that the range is too large. Then, according to the situation observed during the test connection, make corresponding adjustments and then carry out the relevant experiments.
How does the ammeter read
First, find out how much each large grid on the dial represents and how much each small grid represents. As shown in the figure, each large grid represents 0.2A, and each small grid represents 0.02A, which can be accurate to 0.02A at this time. Then look at the position of the pointer. Now the position pointed to by the pointer is 2 large grids and 3 small grids, then the reading of the ammeter should be.
Maintenance method of ammeter
1. Since the overload capacity of the magnetoelectric ammeter is very small, be sure to pay attention to the polarity and limit of the connected circuit when using it s Choice.
2. If the reverse deflection or forward deflection of the pointer is found to exceed the full scale line on the scale during the measurement, the power should be cut off immediately and the measurement should be stopped. Measure again.
3. When the measurement is completed, the power supply should be cut off first, and then the ammeter should be removed from the measurement circuit and placed in a dry, ventilated and cool environment for the sensitivity and accuracy of the micrometer. For the safety meter and the room safety meter, the positive and negative terminal buttons should be connected with wires to protect the measuring mechanism of the meter.
