When you take measurements with a multimeter, you are likely to come across different readings.
It’s important to understand what each reading means to avoid misinterpretation or errors when using the instrument.
You need to know if there’s a short circuit, open-loop, or circuit (OL), or there’s no circuit at all.
This will ensure that you take the necessary safety cautions to prevent damaging your instrument or hurting yourself.
A multimeter or a multitester, as its name implies, is an instrument that can be used to take multiple measurements.
It can test for voltage (volts), resistance (Ω), direct current (DC), and alternating current (AC). More complex and advanced multimeters can also test for temperature, inductance, frequency, diode and capacitance.
The world is evolving, and technology has fast shaped the world. Every gadget or device is electronic or electric.
Thus, getting accurate and precise measurements is important while building, installing, repairing, and servicing these gadgets.
A multimeter is one of the diagnostic tools that is needed to take these measurements.
What Does OL Mean On A Multimeter
What is Open-Loop (OL) reading?
Every multimeter has two probes which are colored black and red, respectively.
Each probe is connected to its respective terminal on the meter. In cases where there’s a discontinuity between the probes, your multimeter displays OL (open loop) or dashed lines on the screen.
This means that there is no path or route for the electric current to flow between the probes.
In Open Loop or Infinite Resistance, there is too much resistance that the multimeter can not measure.
Just like in obstructed pipes or waterways, whenever there’s an open loop, the multimeter assumes that the electric current flow has been hindered and that there’s too much resistance.
When you test for the resistance, it shows OL, indicating there’s no current flow in the meter.
What is a Continuity Test?
A continuity test is a resistance test that helps to differentiate between an Open Circuit or Loop (OL) and a closed circuit.
This test helps determine if the probes are electrically connected and if electric current can move freely between them.
How to perform a Continuity Test with a Multimeter.
- Before you start a continuity test, the first step is to ensure that there is no flow of electric current through the circuit.
- Next, insert the black probe into the common slot (COM) on the multimeter.
- Plug the red probe into the AVΩ port on the meter.
- Switch on the meter.
- Then, turn on the dial and set it to continuity test mode. The logo might vary for different brands or models of the meter. The common symbols include a diode (a diode is a triangle with a line placed on its right side), and a sound wave symbol.
- If your meter does not have this test mode, switch to the resistance mode and turn the dial to the least number. The symbol is indicated by Ohms (Ω). You can also check your meter user’s manual for instructions on switching to continuity test mode.
- Test for continuity by passing a little electric current through the circuit and check if it flows to the other probe.
- Put and hold the metallic parts of the two terminals together. If the probes are electrically connected, the meter displays a number that is less than one (0 or a number close to 0) and beeps. Otherwise, OL (Open Loop) or a higher number is displayed. This indicates that there is no continuity.
- Finally, to complete the continuity test, put a probe at the end of the circuit that you are testing. If there’s a continuous flow of current, the meter beeps and displays 0 or a number near zero. Otherwise, there’s no continuity.
A perfect continuity in the circuit is indicated by 0. Although, other numbers near 0 and less than one are still regarded as safe.
How to Use a Multimeter
The typical readings taken by a multimeter are in volts, amperes and ohms. This article highlights the step-by-step procedure involved in taking each measurement.
How to Measure Voltage
- Before you start taking your readings, make sure to adhere to all the necessary precautions to prevent any harm or damage.
- First, connect power to the electric circuit.
- Select the AC, DC and mVolts as you desire.
- Put the black-colored test lead into the common slot (COM).
- Next, Insert the red-colored test lead into the V input slot or jack.
- Putting the two test leads’ tips to the circuit across a power source or load that lies parallel to the tested circuit.
- Check the readings and take note of the displayed unit.
When you take the Direct Current Voltage of the right polarity, put the red probe to the positive circuit ground and the black one to the negative side.
If you are using a digital multimeter with autopolarity, it will display a negative symbol to indicate the reverse polarity.
If you use an analog instrument instead, you are likely to damage it if you don’t use the right polarity.
How to Measure Current
Taking current measurements with a multimeter is quite different from the other readings.
It involves placing the instrument in series with the tested circuit, opening the electric circuit and using the probes to complete the circuit.
This causes all the current to move via the circuitry of the multimeter.
The other method of taking current readings is indirect, and it involves clamping a current probe around the outside of the conductor. This method prevents the opening of the circuit.
Below are the procedures to take while you measure your circuit current.
- Disconnect the power source to the circuit.
- Cut or disconnect the circuit and make openings for the insertion of the meter probes.
- Select amperes (AC) or amperes (DC) as you desire.
- Input the black test probe in the common jack (COM).
- Put the red test probe into the Amperes or milliamperes jack, depending on the value you expect from the readings.
- Next, connect the tips of the meter probes to the circuit in series. This will ensure that all the electric current moves through the instrument.
- Connect the power source of the circuit back.
- Take the readings and note down the unit of the measurement. If the test probes are reversed for a DC reading, a negative sign will be shown on the screen.
How to Measure Resistance
Short circuits are rare with resistors, but open loops are common. In an open-loop or circuit, the meter’s LCD displays OL because of its infinite resistance.
Before you take your resistance readings, you must put off the power source to the circuit to avoid damaging your meter or the circuit.
Follow these steps to measure your resistance.
- Make sure that the power supply to the circuit is turned off.
- With the rotary selector switch, choose your resistance function (Ω)
- Input the black test probe into the COM input jack while putting the red test lead into the Ω input slot.
- Connect the leads’ tips across the component or section of the circuit that you want to read its resistance.
- Take your readings and make sure to know the unit of measurement – whether it is ohms (Ω), kilohms (kΩ), or megohms (MΩ).
Safety Precautions While Using the Meter test Probes or Leads.
While you use and plug in the test probes during measurements, there are certain safety precautions that you should consider.
One crucial safety tip is that you should never leave the test probes plugged into the input jacks and then take voltage readings afterward.
This can lead to a current shunt, and there will be a direct short across the source volt through a low-ohm resistor inside the instrument.
As a result, high electric current will flow through the meter, and if the instrument is not well protected, it can be damaged.
The circuit can also be affected, and you might get injured. If the circuit’s voltage is very high (240 volts or more) as in industrial circuits, there could be severe fault currents.
Thus, you must provide adequate input fuse protection for the tested circuit.
Avoid using multimeters without input fuse protection on high-voltage circuits with a voltage of more than 240 volts.
Also, make sure that the meter is equipped with a fuse with enough ability to clear out high current or energy damages.
The fuse should have a much higher voltage than the maximum voltage you can record as your reading.
What other functions does a Multimeter perform?
Besides checking the voltage, current, and resistance of a circuit, a multimeter also performs some other important functions. Here are a few:
- Diode Testing or Checking: Certain multimeters have special features that allow you to test the diode on any appliance. Occasionally during your troubleshooting, you might need to test the diode to ensure it’s working properly.
- Capacitance Measurements: There are also specific digital millimeters that can help to test a capacitor. Some analog meters can also perform this function.
- Frequency Readings: A multimeter can be used to calculate frequencies. Although not all multimeter models are equipped with this feature, you should check out to see if the meter you are getting has.
What are the General Safety Precautions and Guidelines necessary while using a multimeter?
If you do not take necessary safety tips while using the multimeter, you could be hurt or get injured. These precautions will help to keep you safe and prevent your meter from getting damaged.
Here are a few precautions to note while taking measurements.
- Whenever the meter is not in use, turn its knob to the off position or the maximum value on the scale. This will help to prevent the multimeter from getting damaged whenever someone else uses it and tries to measure high values while using a sensitive or small scale.
- Check for the Alternating current (AC) and Direct current (DC) voltage whenever you want to test for the presence of a dangerous voltage in a circuit with a multimeter.
- Do a Continuity test before you use the instrument. Connect the metal parts of the terminals and ensure the meter displays zero or near zero. Remember also to put off the power supply to the circuit before you run the test.
- Never attempt to take readings of current in a household. Alternating Current mains as it could be hazardous.
- Ensure that you observe a proper Direct Current polarity when you take DC readings.
- Do not put the bare probe tips together whenever you are taking voltage measurements. This can lead to a short circuit.
- Ensure to connect the meter in series whenever you take measurements in amperes, while you should connect it in parallel for volts measurements.
- Before you take measurements in ohms, disconnect the power to the circuit.
- Before you connect the meter to the circuit, make sure to discharge and de-energize the circuit entirely.
- Take Alternating Current (AC) readings on an AC scale.
- Ensure that the meter is changed to Alternating Current before you take readings for AC circuits.
- Make sure to begin your readings from the highest current or voltage range.
- While taking your readings, pick a final range that allows your reading to be near the middle of the meter scale.
- To prevent your meter’s fuse from getting blown, fix the optimal current range before you take higher current readings.
- Check for the presence of a capacitor in the circuit frequently to avoid any issue. A beep sound indicates the presence of a capacitor in the circuit till the capacitor drains.
- Before you take any resistance readings, alter the 0 ohms reading. Similarly, after you change the resistance ranges, alter the 0Ω.
- Take readings from your resistor alone without connecting to other parts. Else, your readings might be affected.