What Is an Ammeter?
An ammeter is an electrical meter used to measure the magnitude of an electric current. It is a measuring instrument with small internal electrical resistance. The circuit at the point of measurement is disconnected, and the ammeter is connected in series between them. Inside the ammeter, a low resistance is inserted into the circuit, and the voltage at both ends of the resistance is measured and converted to a current value.
A current shunt or current transformer is used to measure large currents. An ammeter is broadly classified into a DC ammeter and an AC ammeter. An ammeter is available in two display types: analog and digital.
In industrial applications, an ammeter is more accurate than multimeters and clamp meters and can measure minute currents.
Uses of Ammeters
Ammeters can be used in laboratories where electricity is used for precise measurements, or they can be fixed to control panels as monitors. There are also cases where the current is checked using a simple tester. Ammeters in multimeters, clamp meters, etc., are used to check power distribution and transmission in homes and buildings.
Some automobile instrument panels are equipped with DC ammeters. A positive reading indicates the battery is charging and a negative reading indicates it is discharging. Ammeters are commonly installed in switchboards of factory equipment, buildings, and power generation equipment. School science experiments teach how to measure current. In laboratories, the current is often measured precisely.
Fine ammeters and totalizing ammeters are also used for plating and surface treatment with fine currents, which require measurement of fine currents.
Principle of Ammeters
Ammeters are connected in series to a circuit. Analog ammeters use a pointer to indicate the current value. The needle of the permanent magnet moves in response to changes in the magnetic field caused by the current flowing through the internal coil. DC ammeters are of the moving coil type and consist of a permanent magnet and a coil. For large current measurements, a current divider is used to extract a portion of the current for measurement.
Ammeters for alternating current are mainly moving iron strip-type instruments and are used to measure commercial frequencies of about 45 to 65 Hz. When measuring current, voltage drops at the connection terminals and indication errors due to heat generation and magnetic fields may occur. Measuring a current greater than a certain value will result in a larger error. To improve the accuracy of current measurement, current dividers are used for DC and current transformers are used for AC.
Ammeters with digital displays use current dividers, current sensing resistors, and AC current sensors. The fine voltage at both ends is then digitized and used as the current measurement value. In addition, an integrating ammeter is used at plating sites. It is possible to measure the totalization of the current that has flowed over a certain period.
Other Information on Ammeters
1. How to Use an Ammeters and Precautions
Ammeters are a measuring instrument that measures the current flowing at a certain point in a circuit. It is made so that its internal resistance is low and does not affect the current flowing in the circuit. When connecting ammeters, insert the ammeters in series with the circuit whose current is to be measured. Connect the higher potential of the circuit to the + side of the ammeters and the lower potential of the circuit to the – side of the ammeters.
There are generally several terminals on the (-) side of the ammeters. If the measurement range is known, select the appropriate range; if not, start with a large range and work down to the appropriate range. If you start with a small range, you may destroy the ammeters when a current greater than the range is applied. Some ammeters are protected by an internal fuse.
A similar instrument is the voltmeter. A voltmeter is connected in parallel to a circuit and measures the voltage between two points. Connecting ammeters to measure voltage in the same way as ammeters is very dangerous because it is the same as shorting the power supply. Therefore, extreme caution is required.
2. Multimeter
There is a useful instrument called a multimeter or tester. They can measure not only current but also basic electrical characteristics such as current, voltage, and resistance, regardless of whether it is AC or DC. There are digital and analog types. They are mainly handy types that can be easily carried around and used.
Current is displayed by measuring the voltage at both ends of a micro resistor inside the instrument and converting it to current. DC voltage is displayed by amplifying the voltage between two probes or by attenuating it through an attenuator. AC voltage is displayed by converting AC voltage to DC voltage through a rectifier circuit.