You may be wondering why you need to know how to use an analog multimeter in a wildly digital age. Well, the reasons are plenty.
As a modern electrician, you never know when and where the need arises for you to read an analog display – whether it is on a multimeter or another measuring tool.
Plus, some applications still use analog meters (also written /as analogue meters) for troubleshooting, owing to their accuracy and true RMS value conversion.
Analog multimeters have a moving needle that stops on a number printed on the background behind the moving needle. The number that the needle stops on indicates the volts, ohms or amps the meter is measuring depending on how the control knob is set.
Analog multimeters are cheaper than digital multimeters but not as robust or simple to use. Some technicians prefer analog multimeters because the needle movement can show you some things that are not obvious with digital multimeters.
What is an analog test meter?
Analog multimeters or test meters are test instruments based around the use of a moving coil meter. This analog form of display uses the deflection of an indicator needle to indicate the level of the measurement being made.
The basic meter used in an analog meter is a moving coil meter, and this deflects from its rest position increasingly as the measurement quantity increases. These meters were a feature of many laboratory views photographed before the 1970s and 1990s when digital technology supplant analog techniques.
The analog test meter typically contained a single meter and movement, and series and parallel resistors were used to provide the correct ranges. Typically a large rotary switch in the centre of the front panel under the meter was used to select the required range.
There are sometimes several different connections used for the probes. There are usually common and standard measurement probe connections. The normal one is often labelled Amps, Volts, Ohms or similar, indicating its usual measurements.
Also, for some measurements with either very high or low current, a different probe connection may be used. These other probe connections may be designated 10Amps for a ten amp range, etc.
It’s hard to visualize electricity, so I’ve always thought of it like a river. In a river, there’s a specific volume of water (similar to electrical amperage, or amps) flowing with one particular potential force (like voltage) that encounters obstructions as it flows (resistance measured in ohms). Hold that big picture in your mind, then add these key concepts about both electricity and VOMs:
- Alternating current (AC) voltage: The type of electricity that powers your house.
- Direct current (DC) voltage: The type found in auto and household batteries.
- Resistance (measured in ohms): The lower the reading, the more manageable the electrical current (measured in amps) flows through the circuit material.
- An open circuit equals trouble: There is high resistance from a broken connection, a faulty part or a switch that’s been turned off. There isn’t a complete circuit path, and no current will flow.
- A closed-circuit is good: It means a minimum of resistance is present because a connection or part is working. Note: Check the wiring or device pathways being tested for any random loose wiring that’s touching the circuit you’re testing. Sometimes a broken connection (“short circuit”) can look like a closed circuit. Short circuits can harm you, destroy equipment and start fires.
- Continuity testing determines if an open, shorted or closed circuit exists in an appliance, electrical or electronic device and is a common use for multimeters.
- On a VOM, infinity signifies an open circuit. On an analog multimeter, infinity shows up as an unwavering needle that won’t move off the display’s far left side. On a digital multimeter, infinity reads “0.L.”
- On a VOM, “zero” means a closed circuit has been detected. The display needle moves to the far right side of an analog scale; “zero” reads “0.00” on a digital VOM.
- Selecting the proper range is very important and refers to setting the function switch on your multimeter to a voltage or amperage value that’s higher than the top value you anticipate testing. Digital multimeters have a nifty feature, auto-ranging, that automatically selects the broadest possible range once you set the function switch for ohms, current and voltage (AC or DC). Auto-ranging gives you the safest testing capacity each time you change back and forth from, say, measuring resistance to voltage readings.
Understanding the Analog Multimeter Scale
Before we can jump into the steps, the workings of an analog meter scale must be fully clear to us.
This is important because we have been so acclimatized that it can become slightly confusing to read the analog scale with our digital tools. Take a look at the image shown below.
Understanding the Panel
In the image, at the bottom left is where your test leads will be connected. It is similar to how you connect the leads in a DMM. The ports in the bottom right are for advanced options.
The optional polarity switch comes in handy when you want to reverse the polarity of your measurement. The switch in the middle is how you select the quantity to be measured and the desired range.
For example, if you want to use an analog multimeter to measure voltage (AC), you would switch it to the dial’s left-hand side.
Some multimeters have different switches for range and quantity selection. Some also have a separate dial for zeroing out the meter, which we will cover later in this guide.
The Analog Scale
Take a look at the close-up image of an analog scale below.
The top line (in black) is the ohmic scale, where you measure the resistance from left to right. Based on the range selected, you will have to multiply the scale reading with the range currently selected. For example, if the pointer is steady at 5 and your range is 1k, your reading is 5k ohms.
The range selection is made similarly for all quantity measurements.
Below the ohmic scale are the voltage and current scales. The black line adjacent to the ohmic scale is where you measure DC voltage and current. The red line is always for AC measurements. Please note that current and voltage measurements are read from right to left.
The chief difference between an analog multimeter and voltmeter/ammeter is the scale. A voltmeter will only have two scales for AC and DC voltage measurement, whereas an ammeter or a galvanometer will only have one scale for AC and DC amps measurement.
Now let’s have a look at measuring some quantities.
How to Use an Analog Multimeter
If you have an analog meter of your own, please follow the steps outlined below –
- Connect the test leads to your analog multimeter
- Use the following setups for measuring different quantities:
- Use an AA battery to measure voltage, DC voltage, and current.
- Use an AC socket to measure AV voltage and current.
- Use a resistor to measure resistance.
- Use a wire to measure continuity.
- For each setup, connect the test probes to the element to be measured and check the scale’s reading. In this guide, we will take the example of measuring DC voltage.
- Connect the probes to either end of the AA battery (approx. 9V). The pointer should move across the scale depending upon the range you have selected. Using the above image, if the battery is fully charged, the pointer should point between 8 and 10 on the scale. If not done, please select the DC volt range in your multimeter that is higher than 10 V (usually 10V or 12V)
- Try the same technique for other setups to measure the respective quantities.
As noted earlier, the key to accurate analog measurement is range selection and multiplication. Everything else is similar to what and how you do use your DMM.
In the above example involving the battery, if you use your analog multimeter to measure a car battery’s voltage, the range must be higher. You will also have to do simple multiplication to get the final measurement.
For example, if your DC volt range is 250V, and the pointer is between 50 and 100, then the voltage is around 75 volts depending upon the exact point.
You have the essential guide on using an analog multimeter to measure voltage, current, and resistance. The basic principle is the same as DMM, but you need to put in more efforts here. We hope that this guide has been helpful.