Can you explain how a voltmeter and ammeter work?

Answer 1

In parallel with the element you wish to measure the voltage across.

Answer 2

When a current-carrying conductor is placed in a magnetic field, the conductor experiences a force which acts to push the conductor out of the field. This is the principle of operation of an analogue ammeter and voltmeter.

A light coil of wire supporting a pointer is placed between the poles of a permanent magnet. Whenever the coil rotates, the pointer sweeps across an appropriately-calibrated scale. When current flows through the coil, a torque acts to rotate the coil. However, the movement of the coil is restrained by a pair of hairsprings. When the torque due to the current is balanced by the restraining torque of the hairsprings, the coil stops rotating. Thus, the angle through which the coil rotates is proportional to the current flowing through it, and the instrument is calibrated such that the pointer directly indicates that value current on a curved scale.

Ammeters and voltmeters both work on the same principle. In the case of the voltmeter, the current which operates the coil is proportional to the voltage appearing across the instrument. The difference between the two instruments is the way in which resistors are used, within the instruments, to make one suitable for measuring current and the other suitable for measuring voltage.

Ammeters must be connected in series with the circuit under test, whereas voltmeters must be connected in parallelwith the circuit under test.

Digital ammeters and voltmeters work on a completely different principle, using an electronic 'gate' to switch on and to switch off a series of pulses. The time for which the gate is 'open' is a function of the value of the current or voltage being measured -e.g. the larger the current, the longer the gate is held open. These pulses are then counted and, in simple terms, the greater the number of pulses counted, the greater the current or voltage being measured. The output is then presented, directly in amperes or volts, on a LED or LCD screen.

For use in the field, analogue and digital multimetersare available. These allow current, voltage, and resistance to be measured using the same instrument.

Answer 3

A voltmeter works by adding a parallel branch with high impedence across two points. Based on the amount of current (measured by electronic components within the meter) that flows through the parallel branch, and the known resistance of that branch, the voltage can be calculated via Ohm's Law.

The idea is to have the impedance be very high compared to the two points, so that the amount of current running through the meter will be very small compared to the current between the two points.

Answer 4

A voltmeter lets you measure the voltage across a load or power supply usually in either AC or DC. Most voltmeters also let you measure resistance in Ohms and Current in Amps.

Answer 5

Measures the voltage between the two circuit nodes it is connected to.