The voltmeter is one of the most useful devices for testing electrical installations in a home, if you know how to use it correctly, of course. If you have a voltmeter, you must learn to make the basic settings and you must test it first in a circuit with direct current (powered by a battery or a cell), before using it in other configurations. In this article, you will only get information about using a voltmeter or multimeter in voltmeter mode. You can click the following link to learn how to use a multimeter.
Part 1 of 3: set up the device
Step 1. Put the device in voltmeter mode, if necessary
Most devices that measure voltages (= voltages = differences in electrical potential) are in fact multimeters with which we can measure different electrical quantities between two points of a circuit. If the device has a switch with more than one measurement scale, then it is a multimeter and then you should point the marked end of the bar of this large round button towards the measurement scale. tensions.
- To measure the voltage between two points of an electrical circuit carrying an alternating current, point the bar of the switch towards V ~, ACV Where VAC. In modern societies, almost all homes are supplied by the electrical network which distributes alternating current.
- To measure the voltage between two points of a circuit traversed by a direct current, point the bar of the switch towards V -, V ---, DCV Where VDC. The batteries provide direct current.
Step 2. Adjust the sensitivity of the voltage measurement according to the maximum voltage that can exist between two points of the circuit to be tested
You must set the voltmeter to the correct gauge to get accurate readings while avoiding damage to the device. If you cannot tune to a precise caliber, it means that your device automatically selects the appropriate caliber before each measurement. If you need to manually adjust the caliber, follow these instructions.
- Choose the gauge that matches the maximum voltage you expect to measure. If you have no idea what voltage you might get, set the unit to the highest rating for safety.
- Usually the voltage of a battery is indicated. Small cells or batteries produce voltages of 9 volts or less.
- Car batteries should generate a voltage of 12.6 volts immediately after being recharged and when the engine is turned off.
- In the majority of countries, the alternating current supplied to the outlet of a wall outlet is at a voltage between 220 and 240 volts, but it can also be between 100 and 130 volts as in the United States (120 V).
- Some voltmeters or multimeters offer millivolts as the smallest gauge. It is a sub-multiple of the volt which is equivalent to one thousandth of this unit of measurement and which has mV for symbol.
Step 3. Touch the voltmeter probes to the two points in the circuit between which you want to measure the difference in electrical potential
In general, there is a red and a black probe which each have a metal tip and a male plug that plugs into the body of the device. You must connect the two probes to the box of the voltmeter according to the following indications.
- The male plug of the black probe must be plugged into the female socket labeled "COM" on the housing of the device.
- You must plug the plug of the red probe into the socket of the box next to which is written a large V. If you do not find a V, choose the socket next to which is written my or who has the lowest number.
Part 2 of 3: measure voltage
Step 1. Hold the probes securely
When you put them in contact with points on the circuit, you must be careful that your fingers do not touch their metal tips. If the lead sheaths of the probes are worn, purchase new probes or wear insulated gloves when taking a measurement.
You should never put the two tips of the probes in contact with each other while they are connected to a circuit, otherwise you risk creating large sparks
Step 2. Touch the tip of the black probe to a point in the circuit
To measure the voltage between two points of a circuit, we put the voltmeter in parallel with the circuit between these two points. In fact, we measure the voltage at the terminals (between the two probes) of the voltmeter which is the same as that between the two points of the circuit. The resistance (R) of the voltmeter being fixed, the voltmeter measures the intensity of the current (I) which crosses it to calculate the voltage (V = RI) at its terminals.
- If you are testing the voltage of a battery, touch the tip of the black probe to its negative terminal.
- If you are testing a European wall outlet, put the tip of the black probe into the neutral hole, which is the left hole when the grounding contact rod is located at the top of the outlet.
- If possible, jam the tip of the black probe into the neutral hole in the socket. Some black probes have a tip equipped with a plastic ball that allows them to be easily blocked in a socket.
Step 3. Touch the tip of the red probe to the other point in the circuit
You put the voltmeter in parallel with the circuit between the two points.
- If you are testing a cell or battery, touch the tip of the red probe to its positive terminal.
- If you are testing a European wall outlet, put the tip of the red probe into the hole that matches the phase, which is the right hole where the grounding contact rod is located at the top of the outlet.
Step 4. Set the voltmeter to a higher caliber if the measurement result indicates that the voltage is too high
To avoid damaging your device, make this adjustment immediately if you get any of the following results.
- “OL” (overload = overload) or “1.” appears on the LCD screen. Note: If you read “1V”, don't worry, as this is a valid result which corresponds to 1 volt.
- The needle reaches the maximum graduation of your analog voltmeter and gets stuck there.
Step 5. Adjust the sensitivity of the voltmeter, if necessary
Adjustments are needed if you read "0V" or nothing is displayed on the LCD of your digital voltmeter or the needle of your analog voltmeter does not move. Try to solve the problem by performing the following operations in order.
- Make sure that the tips of the probes make good contact with two points in the circuit.
- If you don't get any results when you take a measurement on a circuit with direct current, check your multimeter for a button with "DC +" and "DC-" written on it. If so, reverse the setting. If you do not have this button, reverse the positions of the probe tips on the circuit.
- Reduce the caliber by turning the switch one notch. Repeat the operation until you get a valid result.
Step 6. Read off the measured value
If you have a digital voltmeter, you just need to read what is written on the LCD screen. If you have an analog voltmeter, read the next part of this article, as you need to interpret the position of the needle.
Part 3 of 3: use an analog voltmeter
Step 1. Determine the scale of graduation you should use to interpret the results
It should match the measurement scale you selected with the switch. If there is no graduation scale under the needle that corresponds exactly to the caliber selected, choose the one that will allow you to obtain the measured values by making simple multiplications.
If, for example, your device is set to 10V DC, use a graduation scale whose largest value is 10. If you cannot find one, choose one with a maximum value of 50
Step 2. Estimate the needle position using the nearest graduations
Voltmeter scales are linear like any ruler.
If, for example, the needle points to a point that is halfway between the 30 and 40 graduations, you should read 35
Step 3. Multiply the value indicated by the needle if the gauge and graduation scale do not exactly match each other
To obtain the multiplication rate, divide the caliber (in volts) by the maximum value (in volts) of the graduation scale. Multiply the value indicated by the needle by this rate to obtain the value of the voltage measured between the two points of the circuit.