Ammeter
Ammeter, also known as "ampere meter".
An ammeter is a tool for measuring the magnitude of current in a circuit
--In the circuit diagram, the symbol of the ammeter is "circle A"
--The structure of the DC ammeter mainly includes: three terminal posts [there are "+", "-" two terminal posts, such as (+, -0.6, -3) or (-, 0.6, 3)], pointers, scales, etc. (AC ammeter without positive and negative terminal posts)
--Rules for the use of ammeters: :(1) Ammeters should be connected in series in the circuit (otherwise short circuit. ）；
(2) The current should enter from the "+" terminal post and exit from the "-" terminal post (otherwise the pointer is reversed. ）；
(3) The measured current should not exceed the range of the ammeter (you can use the touch method to see whether it exceeds the range. ）；
(4) It is absolutely not allowed to connect the ammeter to the poles of the power supply without passing through the electrical appliance (the internal resistance of the ammeter is very small, equivalent to a wire. If the ammeter is connected to the poles of the power supply, the pointer will be crooked, and the ammeter, power supply, and wire will be burned at worst. ）.
Voltmeter
A voltmeter is an instrument that measures voltage
1) Commonly used voltmeter - voltmeter symbol: V
2) Most voltmeters are divided into two ranges. （0—3V）（0—15V）
3) Correct use: zero adjustment (adjust the pointer to zero scale) parallel (can only be connected in parallel with the measured part) positive in and negative out (so that the current enters from the positive electrode to flow in, from the negative pole to access the outflow) range (the measured voltage can not exceed the range of the voltmeter, use the "touch" method to select the appropriate range.
4) The symbol of the DC voltmeter should be added a _ under V, and the symbol of the AC voltmeter should be added with a wavy line "~" under V
The voltmeter has three terminal posts, one negative terminal and two positive terminal posts
For example, the student voltmeter generally has two positive terminal posts of 3V and 15V, and when measuring according to the voltage size, the range is selected as "15V", each large cell on the dial represents 5V., and each small cell represents 0.5V (that is, the minimum division value is 0.5V.); when the range is "3V.", each large cell on the dial represents lV, and each small cell represents 0.1V (that is, the minimum division value is 0.lV.).
We can use an ammeter to measure the magnitude of the current. The symbol for ammeter is (A).
The AC voltmeter does not divide the positive and negative poles, correctly selects the range, and directly connects the voltmeter in parallel at both ends of the circuit under test.
The voltage measured by an AC voltmeter is an rms value for AC voltage.
Energy meter
Electric energy meter is used to measure electrical energy instrument, also known as electricity meter, fire meter, kilowatt-hour meter, refers to the measurement of various electrical quantities of the instrument, commonly known as electricity meter, fire meter.
By use: industrial and civil meters, electronic standard meters, maximum demand meters, compound rate tables
According to the structure and working principle: inductive (mechanical), stationary (electronic), electromechanical integration (hybrid)
According to the nature of the access power supply: AC meter, DC meter
By accuracy level: commonly used common tables: 0.2S, 0.5S, 0.2, 0.5, 1.0, 2.0, etc
Standard table: 0.01, 0.05, 0.2, 0.5, etc
According to the installation wiring mode: direct access type, indirect access type
According to the electrical equipment: single-phase, three-phase three-wire, three-phase four-wire energy meter.
