How to calibrate an ammeter

An ammeter is a device for measuring current. However, to give an accurate reading, an ammeter must be adjusted correctly. This is done by a process called calibration. Many ammeters are calibrated prior to shipment by the manufacturer. Some are sold with a certificate of calibration, indicating that the work has been done in accordance with relevant national or international standards. However, after a period of usage, some ammeters will require recalibrating.

Connect an external calibrated millivoltmeter to the calibration points of the ammeter, if the ammeter is of the Cantec Systems CA-1550 type. Compare the readings on the two displays. Every millivolt on the millivoltmeter is equal to 1 amp. If the readings differ by more than plus or minus 0.2 millivolts, remove the front panel if you are trained to do so. See the Warnings section; the procedure is very dangerous. Insert the tip of a screwdriver into the trimpot. Turn the screwdriver slowly until the two readings correlate.

Connect the ammeter to a shunt if your ammeter is of the Newmar Digital Instruments DCA DC type. A shunt is a resistor that forces current to pass via a different point in the circuit. Press the “+” key or equivalent. Keep it pressed for ten seconds. When the beep sounds, the reading will reset to zero. This is necessary before starting the calibration proper. Apply a measured current and use the up and down keys to change the reading to match the current. Press the “+” key for less than a second to save the setting.

Insert the tip of a screwdriver into the adjustment screw, if your ammeter is of the Blue Sea Systems Analog AC type. The adjustment screw is in the middle of the dark panel on the front of the instrument. Turn the screw slightly to the right or left as required to realign the meter needle.


Ammeter calibration procedures vary greatly between different models.


Take an appropriate training course before calibrating your ammeter where advised by the manufacturer. Cantec Systems warns that calibration should be undertaken only by those with the necessary skills. Performing incorrect ammeter calibration procedures could lead to injury and even death.

Things You'll Need

  • External calibrated millivoltmeter
  • Screwdriver
  • Shunt
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About the Author

Frank Luger had his first educational resources published in the early 1990s. He worked on a major reading system for Cambridge University Press, became an information-technology adviser and authored interactive whiteboard resources for "The Guardian." Luger studied English literature and holds a Bachelor of Education honors degree from Leeds University.