A multimeter is a tool used to check AC or DC voltages, resistance and continuity of electrical components, and small amounts of current in circuits. This tool will allow you to check to see if there is voltage present on a circuit. Thanks to this feature, a multimeter can help you perform many useful tasks. Start with step 1 to familiarize yourself with the device and learn how to use different functions to measure ohms, volts, and amps.
Steps
Part 1 of 4: Familiarize yourself with the Device
Step 1. Find the face of your multimeter
This has arc-shaped scales visible through the window and a pointer indicating the values read from the scale.
- The arc-shaped marks on the interface can be of different colors to indicate the different scales, so they will have different values. They determine the intervals of magnitude.
- A larger mirror surface that follows the shape of the stairs may also be present. The mirror is used to help reduce what is called "visual parallax error" by aligning the pointer with its reflection before reading the value that indicates the pointer. In the image, it appears as a large gray stripe between the red and black scales.
- Many newer multimeters have digital readings rather than the analog scale. The function is basically the same - you will only have a numerical reading.
Step 2. Find the dial or knob
This allows you to change the function between volts, ohms and amps and to change the scale (x1, x10, etc.) of the meter. Many functions have multiple ranges, so it is important to set them correctly, otherwise they could cause serious damage to the instrument or the operator.
Some testers have an "Off" position on this switch, while others have a separate switch to turn off the multimeter. The meter must be set to "Off" when you put it away and is not in use
Step 3. Locate the openings in the case where you will be able to insert the test leads
Most multimeters have several jacks used for this purpose.
- One is usually labeled "COM" or (-), which stands for common. This is where the black lead will be connected. It will be used to make almost any measurement.
- The other jack (s) should be labeled with "V" (+) and the Omega symbol (an upside down horseshoe) for volts and ohms, respectively.
- The + and - symbols represent the polarity of the probes when they are set to test a DC voltage. If you have installed the leads as suggested, the red one should be positive with respect to the black one. It is good to know when the circuit under test is not labeled + or -, as is usually the case.
- Many testers have additional jacks that are required for current or high voltage testing. It is equally important to have the cables connected to the correct jacks, just as it is good to have already set the selector to the type of test (volts, amps, ohms). Everything must be correct. Consult the tester manual if you are unsure which jacks should be used.
Step 4. Try to locate the cables:
there should be two cables or probes. Generally one is black and the other red. They are used to connect to whatever device you want to test and measure.
Step 5. Find the battery compartment with the fuses:
usually found on the back, but sometimes on the side. It contains the fuse with possibly a spare and the battery that powers the tester to measure the resistances.
The multimeter can have more than one battery and there can be different sizes. A fuse is provided to help protect the movement of the tester. Sometimes there is more than one fuse. A good fuse is required for the tester to function. You will also need fully charged batteries for resistance / continuity tests
Step 6. Find the zero adjustment knob:
it is a small knob that is usually found near the dial labeled "Ohm Adjustment", "0 Adjustment" or similar. This is used only with a range of ohms or resistance, as the probes are shorted, causing them to touch each other.
Turn the knob slowly to move the needle as close as possible to the 0 position on the ohm scale. If new batteries are installed, it should be easy to proceed: a needle that will not go to zero will indicate weak batteries that need to be replaced
Part 2 of 4: Resistance Measurement
Step 1. Set the multimeter to OHM or RESISTANCE
Turn the meter on if it has a separate power switch. When the multimeter measures resistance in ohms, continuity cannot be measured, because resistance and continuity are opposite. When there is little resistance, there will be a great deal of continuity and vice versa. With this in mind, you can make assumptions about continuity, based on the measured resistance values.
Find the Ohm scale on the dial. It is usually the topmost scale and has the values placed at the top left of the dial ("∞" or an "8" placed horizontally for infinity), gradually descending towards 0 on the right. This verse is opposite to that of the other scales, which have increasing values from left to right
Step 2. Look at the multimeter's indication
If the leads do not touch anything, the needle or pointer of an analog counter will rest on the leftmost position. This represents an infinite amount of resistance or an open circuit. Furthermore, it can be said with certainty that there is no continuity between the black and the red probe.
Step 3. Connect the test leads
Connect the black lead to the socket marked "Common" or "-". Then connect the red cable to the socket marked with Omega (Ohm symbol) or with the letter "R" next to it.
Set the range (if provided) to R x 100
Step 4. Touch the probes at the end of the cables together
The meter pointer should move all the way to the right. Locate the ZERO ADJUSTMENT knob and turn it so that the counter indicates 0 (or goes as close to 0 as possible).
- Note that this position is the indication of "short" or "zero ohms" for the amplitude of R x 1 values of this tester.
- Always remember to reset the tester immediately after changing the resistance ranges, otherwise you will get an erroneous reading.
- If you cannot get a zero ohm indication, this can mean that the batteries are weak and need to be replaced. Repeat the previous zeroing step with new batteries.
Step 5. Measure the resistance of something like a light bulb that you know works
Find the two electrical contact points on the light bulb. They will be the threaded base and the center of the bottom of the base.
- Have a helper hold the bulb only by the glass bulb.
- Press the black probe against the threaded base and the red probe against the center on the bottom of the base.
- Watch the needle move from the rest position on the left as it quickly moves to 0 on the right.
Step 6. Try different interval widths
Change the multimeter's range to R x 1. Set the counter for this range to zero again and repeat the previous step. Notice how the meter didn't go as far to the right as before. The resistance scale has been modified so that each number on the R scale can be read directly.
- In the previous step, each number represented a value that was 100 times greater. So before 150 was really 15,000. Now, 150 is only 150. If the R x 10 scale had been selected, 150 would have been 1,500. The selected scale is very important for making accurate measurements.
- After this clarification, study the R scale. It is not linear like the other scales. The values on the left are more difficult to read accurately than those on the right. Try to read 5 ohms on the meter while in R x 100 it would seem 0. It would be much easier with the R x 1 scale instead. This is why, during the endurance test, you need to adjust the range so that the readings can be taken in the middle rather than on the far left or right.
Step 7. Test the resistance between your hands
Set the tester to the highest R x value possible and zero the tester.
- Weakly hold a probe in each hand and read the multimeter. Squeeze both probes firmly. Notice that the resistance has reduced.
- Let go of the probes and wet your hands. Still keep the probes. Note that the resistance is even lower.
Step 8. For these reasons, it is very important that the probes do not touch anything other than the device to be tested
If your fingers provide an alternate path around the device, such as when touching the probes, a device that has burned out will not mark "open" on the meter during the test.
Testing of older style cartridge and vehicle glass fuses will indicate low resistance values if the fuse is placed on a metal surface during the test. Instead of trying to determine the resistance across the fuse, the tester indicates the resistance of the metal surface on which the fuse rests, an alternate path being provided between the red and black probe around the fuse itself. Any fuse, working or bad, will indicate "good", giving you a wrong analysis
Part 3 of 4: Measuring the Voltage
Step 1. Prepare the tester for the maximum range provided for AC voltage, ie alternating
Many times the voltage to be measured is an unknown value. For this reason, the widest range possible should be selected so that the circuit and movement of the multimeter are not damaged by a higher voltage than expected.
If the meter were set for a range of 50 volts and tested a very common American electrical outlet, the 120 volts present could damage the instrument irreparably. Start with high values and work towards the lowest range that can be safely displayed
Step 2. Insert the test probes
Insert the black probe into the "COM" or "-" jack. Next, insert the red probe into the "V" or "+" jack.
Step 3. Locate the voltage scale
There can be several VOLT SCALE with different maximum values. The range chosen by the selector determines which voltage scale to read.
The maximum value scale should coincide with the selector ranges. The voltage scales, unlike the OHM SCALE, are linear. The scale is accurate anywhere along its length. Of course it will be much easier to accurately read 24 volts on a 50-volt scale than on a 250-volt scale, where the value could appear to be anywhere between 20 and 30 volts
Step 4. Try a common electrical outlet
In the US, you might expect 120 volts or even 240 volts. In other places, 240 or 380 volts may be expected.
- Press the black probe into one of the straight holes. You should be able to insert the black probe until the contacts behind the face of the socket have grasped it firmly, as happens when you insert a plug.
- Insert the red probe into the other straight hole. The tester should indicate a voltage very close to 120 or 240 volts, depending on the type of outlet.
Step 5. Remove the probes and turn the selection knob to the lowest available range that is still greater than the voltage indicated, 120 or 240 V
Step 6. Reinsert the probes as described previously
The meter this time can indicate 110 to 125 volts. The range of the multimeter is important for obtaining accurate measurements.
- If the pointer does not move, it is likely that DC voltage has been chosen instead of AC voltage. AC and DC modes are not compatible. Needs to correct mode be set. If not set correctly, the user may mistakenly assume that there is no voltage present. This mistake could be fatal.
- Make sure you try BOTH modes if the pointer doesn't move. Set the meter to AC voltage mode and try again.
Step 7. Try not to keep both
Whenever possible, try to connect at least one probe so that you don't need to hold both in your hand while practicing. Some multimeters have accessories that include alligator clips or other types of clamps that will help you do this. Drastically limiting your contact with electrical circuits reduces the chance of burns or injuries.
Part 4 of 4: Current Measurement
Step 1. First make sure you have measured the voltage
You need to determine if the circuit is AC or DC by measuring the circuit voltage as described in the previous steps.
Step 2. Set the counter for the widest supported AC or DC AMP range
If the circuit to be tested is AC, but the meter only measures DC amps or vice versa, stop. The meter must be able to measure the AC or DC amperage in the circuit in the same mode as the voltage, otherwise it will indicate 0.
- Be aware that most multimeters will only measure extremely small amounts of current, on the order of µA and mA. 1 µA is 0.000001 amperes, while 1 mA is worth 0.001 A. These are the current values that flow only in the most delicate electronic circuits and are literally thousands and even millions of times lower than the values seen in household and automotive appliances that a landlord would be interested in testing.
- For reference only, a typical 100W / 120V light bulb will transfer 0.833A. This amount of current would likely damage the multimeter beyond repair.
Step 3. Use a jaw ammeter
Ideal for the home, this tester was used to measure current through a 4700 ohm resistor with 9 volts in DC.
- To do this, insert the black probe into the COM or "-" socket and the red probe into the "A" socket.
- Break the circuit.
- Open the part of the circuit that needs to be tested, one metal end or the other of the resistor. Insert the meter in series with the circuit to complete the circuit. The ammeter is put in series with the circuit to measure the current. It cannot be placed across the circuit in the way the voltmeter is used, otherwise the meter will likely be damaged.
- Respect polarity. Current flows from the positive side to the negative side. Set the current range to the highest value.
- Apply power and adjust the tester range down to allow correct reading of the pointer on the dial. Do not exceed the range of the multimeter, otherwise it could be damaged. A reading of about 2 milliamps must already be indicated by Ohm's law: I = V / R = (9 volts) / (4700 Ω) = 0.00191 amps = 1.91 mA.
Step 4. Watch out for any capacitive filters or anything else that causes a power surge on power-up (overcurrent)
Even if the operating current is low and within the tester's fuse range, the overcurrent can be many times higher than the operating current, as discharged capacitors are almost a short circuit. Failure of the tester fuse is almost certain if the current flow of the DUT (Device Under Test) is many times higher than that of the fuses. In any case, always use the fused upper range measurement of the highest value and be careful.
Advice
- If the multimeter stops working, check the fuse. You can replace it in places like Radio Shack and the like.
- When you are going to check any part for continuity, you need to remove the power. The ohmic testers are powered by an internal battery. Leaving power off while measuring resistance will damage the tester.
Warnings
- Do not connect never the meter through a voltage source or battery if it is set to measure current (amps). This is a common way to blow a tester.
- Respect electricity. If you don't know something, ask someone more experienced.
- Check it out always testers on voltage sources of known voltage to verify their operational status before use. A broken meter that measures voltage will indicate 0 volts, regardless of the amount present.
