How to Use an AC Ammeter

Written by mark stansberry
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How to Use an AC Ammeter
An ammeter has a black and a red measurement lead. (multimeter image by dinostock from

An AC ammeter, or alternating current ammeter, is used to measure alternating electrical currents, which are electrical currents whose electrical current level varies with time. When an AC meter is used to measure alternating current, the AC ammeter continually makes electrical current measurements and then averages that current measurement with the previous measurements. The reading on the AC ammeter's display is this average measurement.

Skill level:

Things you need

  • Ammeter's operators manual
  • Elementary electronics laboratory book
  • Elementary electronics book
  • Electronics safety guidebook
  • Wire cutters

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  1. 1

    Turn off the power to the electronic circuit or wires where you plan to make the AC current measurement. Before you connect an AC ammeter, read the operator warning and safety instructions. Make sure you are knowledgeable about the dangers of working with AC voltage and current. Remember that AC electrical current has the potential to cause severe electrical shock and even death.

  2. 2

    Connect the ammeter in series with the electrical current you want to measure. Remember that current flows through a wire like water flows through a pipe. To make a proper AC ammeter connection, the connection must be so that the electrical current you are measuring will flow through the ammeter.

  3. 3

    Cut the wire where the electrical current measurement is to be made after once again ensuring that the power is off, and that all electronic components in the circuit have been discharged. Also be sure to wear and use the appropriate electronic safety gear. .

  4. 4

    Connect the ammeter's positive probe to one of the wire's loose ends. Next, connect the ammeter's negative probe to the loose wire's other end. Reconcile with yourself that with this arrangement, after power is turned back on, the electrical current will flow out of the first end of the wire, into the ammeter's positive probe, through the ammeter, then out of the ammeter's negative probe and back into your circuit.

  5. 5

    Turn on the power. Note the reading on the ammeter's display. Understand that autoranging ammeters let your read the current directly from the display without making any calculations. Also understand that ammeters without autoranging will require that you change the range setting to display the AC current measurement.

  6. 6

    Lower the current range of the ammeter if your ammeter isn't an autoranging model and therefore displays a value of zero. Increase the current range setting if the ammeter displays an under range error.

Tips and warnings

  • Make sure you understand the range settings on the ammeter, if any. Remember that autoranging ammeters don't have range controls; instead, they automatically set the ammeter to the right current measurement range.
  • On ammeters that have range settings, typical ranges include the 0.1, 1, 10 and 100 milliamperes range.
  • Remember that to obtain any measurement at all or an accurate current reading, the ammeter range must be set to the right value. Consider that a current of 1.2 milliamperes cannot be measured with an ammeter that is set to the 0.1 milliampere range. Also consider that current of 0.05 milliamperes cannot be measured accurately on the 100 milliampere range. Remember that the rule for range selection is to pick the range that is closest to the electrical current value being measured.
  • Review ammeter operator and instruction manuals for different types of ammeters and different manufacturers. Consider that there are lots of different types of ammeters and although most operate on the same principles, operating them can be quite different. Also consider that some ammeters are used for measuring very high currents, some are used for measuring very low currents and others are used for making very accurate current measurements.
  • Consider that an ammeter's control buttons may have to be selected to measure current for different types of current waveforms such as square and sinusoidal waveforms. Read your operators manual to find out what types of current waveforms it can accurately measure and what controls have to set to make those measurements.
  • Set the AC ammeter for the type of alternating current measurement you want to make. Consider that an ammeter may have controls that need to be set for making average, rms, peak or peak to peak current measurements.
  • Before you connect your ammeter, turn off the power to the circuit that you plan to measure. Consider that you don't want to handle electronic components that have current flowing through them. This could result in electric shock or electrocution.
  • Discharge all electronic components that may have retained an electric charge after power has been turned off. Remember that capacitors, inductors, transformers, relays and other electronic components may still hold an electric charge long after the power source or plug has been removed. Consider that if you handle these devices while they still are charged, or electrically hot, they may have enough power stored to cause a serious burn or death

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