How to Read an Analog Voltmeter
While many modern voltmeters use a digital interface, an older analog voltmeter will still use the older needle-and-graph interface to display amperage, voltage and other readings. This guide will teach you how to read an analog voltmeter.
Step 1 - Determine the Indicator Gap Differential
First you will need to figure out the indicator gap differential. This is the amount that the reading increases between each hash mark on the analog graph scale. You can determine the value of each hash mark by a dividing the number of marks by the difference in the placeholder values. For instance, if there are eight hash marks between 0 and 0.4, the incremental increase of each mark would be 0.05.
Step 2 - Determine the Range Scale
Many voltmeters will come with a range scale that makes working with large or small reading numbers easier. In most cases, you will simply need to multiply the value of the needle's location with the range that is selected. For instance, if you are using your voltmeter to measure resistance, you would multiply the needle reading times the R-value selected on the voltmeter.
Step 3 - Interpret the Reading Results
In order to interpret the reading of the voltmeter accurately, you need to carefully determine the value of the needle on the graph and then multiply it by the selected range setting on your voltmeter. Whether you are measuring for voltage, resistance or continuity, the process is basically the same.