What is ammeter?
An ammeter is a measuring instrument used to measure electric current. It is designed to be connected in series with the circuit or component through which the current is measured. The ammeter provides a low resistance path for the current to flow through, allowing it to measure its magnitude accurately.
Different ways to measure current
Principle of ammeter?
The basic working principle involves using a shunt resistor or a current-sensing mechanism. The shunt resistor is placed in parallel with a galvanometer (within the ammeter), and the entire ammeter is in series with the circuit under measurement.
The shunt resistor creates a voltage drop across it. This voltage drop is proportional to the current flowing through the ammeter. By measuring the voltage across the shunt resistor, the ammeter can calculate the current passing through it using Ohm’s law (V = I * R), where V is the voltage, I is the current, and R is the resistance of the shunt.
Types of ammeter
Analog ammeter
In Fig 1,
- Ri = Internal resistance of an ammeter/galvanometer.
- Rsh = Shunt resistance; this will carry the majority of the current.
- Vg = Voltage across the Rsh
- Ig = Galvanometer current
- Iload = Ish + Ig
In Fig 2(a), A Galvanometer is used to create an Ammeter. A galvanometer is a device that detects presence of current. Fig 2(b) shows how an ammeter is used in a circuit to measure current. The ammeter is inserted in series to measure the current.
Amplified analog ammeter
In an amplified ammeter (as shown in Fig 3), the sensitivity can be increased manifold if a precision amplifier is used after the Vg is generated. It would allow the use of very low Rsh that will help reduce the voltage drop across it.
Digital ammeter
Unlike analog ammeters, which use a mechanical pointer and a calibrated scale, digital ammeters display the current readings as numerical values on a digital screen. They are based on microcontrollers/ASICs.
The working principle of a digital ammeter involves using current sensing mechanisms, such as Hall effect sensors or Shunt resistors. The Hall effect sensor detects the magnetic field generated by the current flowing through a conductor and converts it into a proportional electrical signal. The shunt resistance creates a voltage drop across it, amplified to a usable voltage. The generated signal is then processed by electronic circuitry, including analog-to-digital converters (ADCs), to convert the analog signal into digital data.
The digital data is then displayed on a digital screen, which may be an LCD (liquid crystal display), LED (light-emitting diode), or other types of digital display. The digital readout typically shows the current value directly in amperes (A) or milliamperes (mA), depending on the range of the ammeter.
Digital ammeters offer several advantages over analog ammeters, including:
High accuracy: Digital technology provides greater precision and reduces the chances of reading errors due to parallax or misinterpretation of analog scales.
Multiple ranges: Digital ammeters often have multiple ranges, allowing them to measure a wide range of currents and automatically switch between the appropriate range based on the current being measured.
Enhanced features: Some digital ammeters may have additional features like data logging, peak current capture, min/max current readings, and communication ports for data transfer.
Compact and easy to read: Digital displays are typically more compact and easier to read, especially in low-light conditions.
Reduced loading effect: Digital ammeters usually have higher input impedance than analog ones, causing less disruption to the measured circuit.