Ammeter or ampere meter is a tool that serves to measure the strength of electric current in a closed circuit with units of amperes or with the symbol A, or milliampere with the symbol mA. 1 Ampere conversion equals 1000 mA.
Ammeter is a mandatory tool that must be owned by an electrical technician. This electric measuring instrument works according to the rules on the Lorentz force generated by the magnetic field-coated coil which produces a larger deviation as the electric current increases.
This instrument is very vital in domestic level or industrial level related to electricity. Technicians will definitely need an ammeter to carry out a series of tests related to electromagnetism and the behavior of electric currents in order to further identify and make decisions about making repairs.
There are two types of ammeters based on electric current, namely AC ammeters to measure alternating current, and DC ammeters to measure one-way electric current or direct current.
Types of ammeters based on how they work are divided into several types, including:
- Thermal ammeters, work using the law of Joule expansion where the heat generated by an electric current is proportional to the square of the current.
- Electromagnetic ammeters are made by combining the interaction of conductors carrying an electric current or magnetic field.
- Hook ammeters are considered very practical, because when you use them you don’t have to open the circuit and can be used to measure AC or alternating current.
To be able to work properly, the Ammeter consists of several main parts, namely:
1. Galvanometer
Galvanometer is a tool that works using the Lorentz principle which is made of an iron core covered with a very fine coil of wire. It can measure electric current with very high accuracy.
The iron core is supported by a shaft that has little resistance to movement, where the coil is placed between the two poles of a permanent magnet.
When an electric current flows through this coil, the iron core will become a magnet and get attracted to the magnetic poles one way or another depending on the polarity of the connection. The core then rotates and the pointer or needle will show the intensity on the ammeter scale.
To enlarge the measuring limit of the ammeter, the galvanometer is arranged in parallel with a resistance or resistor that has a low resistance value.
2. Positive and Negative Terminals
The positive terminal on the ammeter serves as a positive input for the current output charge, while the negative terminal on the ammeter serves as a negative output for the current input charge.
3. Measuring Limit
Measuring Limit is a unit of maximum value that can be measured on an ammeter.
4. Maximum Scale
The maximum scale is a display on the panel that displays the highest value limit, to measure the resistance value, the value is seen from right to left. Meanwhile, to measure current, AC or DC voltage, the value is seen from left to right.
5. Shunt Resistance
A shunt is a component in an ammeter that serves to create a path of low resistance in electric current that allows it to pass through other points in the circuit.
The shunt resistance has a value equal to or less than 1 ohm. This is to prevent any deviation or wrong current measurement method when the ammeter is connected to the circuit.
6. Needle Meter or Pointer
Is a component that is placed on an iron core and coil to help show the value on an analog scale. In a digital ammeter the value on the scale is indicated by a display in the form of digital numbers.
Difference between Ammeter and Voltmeter
Ammeters and voltmeters have the same main components as galvanometers, except that two resistor coils are added to the voltmeter. Voltmeters measure voltage across two points or electromotive force, so you don’t need to disconnect the circuit.
While the ammeter measures the flow or intensity of current in a closed circuit so you need to disconnect the circuit.
How to Use Ammeter
The first thing you should pay attention to is the current in the circuit you are measuring. If you measure a circuit that has a current that exceeds the maximum measurement limit, the components in the ammeter will be damaged or malfunction.
Use the ammeter according to the instructions for both vertical and horizontal use according to the ammeter design. This is intended so it will not affect the assessment of the meter needle or ammeter pointer.
Make sure the ammeter you are using has been set or calibrated before use. Do not connect the ammeter to high-voltage circuits such as batteries because this can damage the ammeter instrument and is also dangerous for the user.
How to Calculate Electric Current with an Ammeter
In a measurement recorded, there is an information that shows the number 50 on the pointer. While the maximum limit listed on the ammeter scale is 100 with a measuring limit of 0.2 A. How much electric current in the circuit?
Answer:
The known data are as follows.
- Designated scale = 50
- Maximum scale = 100
- Measuring Limit = 200 mA or 0.2 A
Then 50/100 X 0.2 = 0.1 A
Then the magnitude of the electric current in the circuit is 0.1 A.