A Complete Guide to Ammeters

The name ‘ammeter’ is an abbreviation of ‘ampere meter’. An ampere, or more familiarly, ‘amp’, is the fundamental unit of active electric current. So, just what is an ammeter?

It clearly follows that the function of an ammeter is to measure that current within an electrical circuit. Ammeters measure current in two metrics - ‘draw’, the flow of current in a particular circuit, and ‘continuity’, the steadiness of the current and the presence or absence of interruptions.

Ammeters are used to detect problems in electrical circuits - unusually high or low levels of current, for example. The former can indicate malfunctioning components for a short circuit, while the latter can be a sign of disruptive interruptions or unusual electrical impedance. It is routine to check sockets or outlets using an ammeter when conducting repairs or changing a fuse.

Ammeters are not to be confused with voltmeters, which measure the voltage in a circuit. Voltage, also known as ‘electrical tension’, is the difference in electrical potential between two points in a circuit and therefore the amount of force required to move charge between them.

Analogue ammeters - also known as analogue panel ammeters - display their readings on an analogue dial with the help of a pointer.

There are three principal types of analogue ammeter. These are as follows:

Moving Iron Ammeters

These models feature an iron needle attached to a vane which moves in response to the electromagnetic force generated by a coil surrounding a second vane within the device. They respond to both alternating (AC) and direct currents (DC). Moving iron ammeters are widely used within industry to measure AC circuits.

Moving Coil Ammeters

These feature a coil which moves in response to the magnetic fields generated by direct current. They cannot function directly with AC.

Moving Magnet Ammeters

These models work in a similar way to the moving coil design, but the electrical coil is located within the meter case and a permanent magnet moves the needle in the dial. They are relatively high capacity, carrying and measuring significantly stronger currents than moving coil models.

Digital ammeters are also known as digital panel ammeters, and as the name indicates, they make use of digital panels to display their reading. This means that they are well suited for use in low light environments. They are a popular choice within factories and similar industrial environments.

Typically, digital ammeters are designed for installation on larger control panels and they are usually programmable. This means that different colours, alarms or messages can be displayed in varying circumstances. It is also usually possible to set the ammeter to trigger when current levels reach or drop below predefined stages.

When selecting a digital ammeter for a particular application, it is important to consider the following factors:

• The minimum and maximum operating temperature required
• The amp measurement range required

Current clamps are a different type of device for measuring electrical current, widely used by electricians. They feature a pair of insulated, plier-like jaws which close over the wire or conductor, allowing measurement without the need for disconnection. When combined with an ammeter, the resulting hybrid devices are known as clamp-on ammeters, clamp meters or just amp clamps.

Typically, they feature a short extension cord which allows the device to separately access the dual conductors within electrical cables. However, some recent models also feature multiple sensor coils within the jaws, allowing the ammeter to access and measure up to three conductors within a cable, with no need for separation.

When combined with a transformer, clamp meters can comfortably measure high currents, but they are less suited to low currents in the milliampere range. It’s also worth noting that some models may only provide approximate readings.