One of the key areas in engineering is instrumentation. Engineers want to monitor and control the parameters of machines so that they can work efficiently. A meter is a device used to measure the quantity of a given parameter. Technicians in their work need to know not only the presence given by indicators but as well how much. When trading items or billing services quantity to be exchanged is of critical value. The post highlights one of the key electrical measuring instruments, the ammeter.
This is an instrument that measures the rate of flow of electricity in form of electric current in a circuit. An ammeter is formed by two separate words; ‘am’ which is short for ampere, the standard unit for measuring electric current, and meter which meter to measure the quantity of a parameter. Electric current flows from the source to the load (power-consuming device) and gives the measure of electricity consumed by a device in a closed circuit.
The working principle of Ammeter
Ammeter works on the basis of three electrical phenomena namely; magnetic field, electric current, and physical force. Oersted discovered in 1020 that electrical current induces a magnetic field and when two magnetic fields are in proximity, they either attract or repel. The first device was analog in nature however when the digital world set in, there have been designed digital one. The ammeter is always connected in series with the circuit to measure the current flowing through it. It’s completely forbidden to connect it in parallel, as this will make its protection fuse to burn and destroy the device. The resistance across it is very small and acts as a short circuit.
The analog ammeter has a coil whose ends are connected to the circuit in series. A magnetic field is created around it from a permanent magnet or electromagnet. When an electric current flows through the coil, the induced magnetic field reacts with the magnetic field around it to cause physical displacement of the coil. The coil has a pointer that moves with it against a scale that gives the magnitude of the displacement. The high the current, the higher the magnetism and the higher the movement of the coil.
Due to its low resistance, a large current will burn the device. To achieve this, a resistor with small resistance than the ammeter is connected in shunt or parallel to it, which will divert more current it and allow measurable current to pass through the ammeter a multiplying factor is then set to give the actual current. A high voltage circuit is usually fitted with a current transformer that lowers the voltage to a value that causes a small current to pass through the ammeter. The turn’s ratio is factored in to give the actual current. For the digital ammeter, the voltage across the shunt resistor is measured as it is proportional to the current through the ammeter. The voltage value is converted to its digital equivalent using an analog to digital converters.
Types of An Ammeter
The two broad categories are direct current and alternating current types. This owes to the fact that current is a directional parameter. The subcategories include;
- Moving coil – it has a permanent magnet around the coil as a source of the magnetic field and measures dc current only.
- Moving iron – it has soft iron as an electromagnet when current flow the induced magnetism reacts with induced magnetism of the coil to deflection of the pointer. It can measure both ac and dc current.
- Electrodynamic– this is a dynamic one as it can measure both ac and dc without the need to calibrate the meter.
- Rectifier– this a permanent magnet type with an additional rectifier to convert ac to dc hence allowing it to be measurable.
There are a wide range of application, given below are some of them;
- Industrial control and monitoring of machines- used by operators to check how much current is drawn by machines and decide on regulation.
- Power generation, transmission, and distribution firms- to determine the quantity of electricity generated or supplied. This is done along with a voltmeter and energy meter.
- Technicians when servicing equipment.
The three most basic parameters in electricity are current, voltage, frequency and current allow the measure of electricity generated or consumed quantifiable and hence billing to be possible. Remember electricity cannot be seen with naked eyes and with a meter we get to see how much is there. I trust the piece has given basic information that can push you farther into the electrical world. A word of caution never does something unsure by yourself instead engage qualified personnel.