A multimeter is – simply put – an ammeter. Not only as a hobby electrician, but you will also benefit from the digital multimeters presented here when working with electricity. High-quality multi-function current meters make your work on the construction site, in scientific research and in electrical companies easier. In addition to professional current testers, we present variants that are ideally suited for use in the hobby sector.
Consult the guide to find out how modern digital multimeters work and how best to use them. The handy measuring instruments are available in various sizes and models. If required, many models can be easily carried in a jacket pocket or have retaining clips for the belt.
The Fluke 175 and Fluke 177 are some popular digital multimeters available worldwide. Which one is best for you, you may ask? I recommend having a look at the comparison and review here: Fluke 175 vs 177
A DMM (digital multimeter) is an electronic measuring device for current. It clearly shows the measured values as numerical values on the display. You can use it to carry out a variety of current tests. Even inexpensive measuring instruments for hobby use measure the standard values of electrical voltage, electrical current and ohmic resistance. This is usually possible in direct current circuits as well as alternating current (AC or DC). High-quality professional current meters have additional features and continue to measure:
An acoustic signal tone is usually available for continuity measurements. In a digital multimeter, the signals are recognized by an analog-to-digital converter and shown as a numerical value on the display. This is usually illuminated and the digits are displayed very largely. This allows you to quickly record the measured values without having to bring the multimeter close to your eyes. You can test current in the measuring ranges from 200 millivolts to 1,000 volts, as well as from 20 µA to 20 A.
Depending on the manufacturer, some digital current testers may deviate from these values and limit the measuring range. The built-in high internal resistance of a digital multimeter is generally between 1 and 20 MΩ, most current meters have a resistance of 10 MΩ.
Measure current and voltage accurately, for DC current measurements the error tolerance is less than 1 percent.
High-quality digital multimeters test circuits even more precisely and have an error tolerance of less than 0.2 percent. However, such devices are usually relatively expensive.
To test the current intensity, the device measures the voltage via a switchable shunt resistor. This is a term from electrical engineering, also known as a current measuring resistor or shunt resistor. This electrical resistance is low impedance and is used to measure electrical current.
When current flows through the shunt, it causes a voltage drop that is proportional to its strength. The digital multimeter measures this voltage drop converts it into a value that can be displayed and shows it on the display. Many instruments have a data-hold function that allows you to easily save the measurement results.
Even when measuring resistance, the device detects the voltage that exists in the circuit under test. The measured values on the display are calculated by the device on the basis of a constant current source. It can be assumed that a constant electric current flows within an electric circuit, which is constant at all points of the circuit regardless of the electric voltage at the connection points.
In the automotive industry, multimeters are mostly used to diagnose car electrical problems. However, you can use your compact current tester wherever you want to test an electrical circuit. Many meters also work contactless, so you can check the wiring in the wall. Common applications for True RMS multimeters are
Direct current flows constantly in the same direction, and its strength does not change. Often colloquially direct current and direct voltage are confused with each other, whereby direct voltage sources generate a direct current in the circuit.
The abbreviation DC for direct current comes from the English and stands for “direct current”.
Special mechanisms allow direct current to be generated from alternating current; all that is needed are so-called “rectifiers” which are built into the electrical circuit. Most electronic household appliances, such as computers, radios or televisions, use direct current for proper operation. The socket in the wall, however, emits alternating current. The necessary rectifiers can be built directly into the electrical appliance, but usually, an adapter or appropriate power supply is used to convert the current.
With alternating current, the direction, also called polarity, changes constantly in regular repetitions. The positive and negative instantaneous values complement each other in such a way that the current is zero on average over time. If direct current and alternating current occur together in an electrical circuit, it is called mixed current. More alternating current than direct current is produced worldwide. The production of alternating current is comparatively simple; the direct current required for many electrical appliances can be easily converted or transformed.
The single-phase alternating current commonly used in households is generated by transformers, which are connected to each other and fed with three-phase alternating current.
AC is used at high frequency, especially in electromedicine and also in communications engineering.
If you want to charge a sensitive device, such as a smartphone, on a gasoline generator, the electricity generated must be converted in any case. If this does not happen, the electrical device will most likely break down and cannot be repaired due to the heavy overload in the electronic components.
With a portable current tester, you can easily determine whether elements of your circuit are electrically connected. This is the so-called continuity test. With some devices, you also receive a visual and acoustic confirmation if the electric current flows unhindered. With most multimeters, you will hear a clear beep if the tested circuit is not live.
In this case, stop the measurement and check all components for defects (e.g. broken cables), check all soldered connections for quality and check the fuses. After troubleshooting, a repeated current test can be performed to inform you about the success and progress of your repair.
The measuring tips, which are attached to a red and a black test lead, are connected to the multimeter while the multimeter is still switched off. Connect the black test lead to the COM port and the red test lead to the output on the instrument labeled VΩmA.
Now switch on your multimeter and select the respective setting with the rotary switch, e.g. current continuity test. Most digital multimeters have a symbol at this point that looks like a shaft. Please refer to the operating instructions supplied with your multimeter for details on the labeling of your current tester, as the display may vary from manufacturer to manufacturer.
Especially measuring instruments from abroad (Asia, America, Great Britain) may differ in the symbols on the device. Do not be afraid of a short circuit! If you have accidentally set a wrong measuring range, the multimeter will warn you with a beep.
For a continuity check, the digital multimeter sends a small amount of current through one test lead and checks up to three times a second whether the other test lead is receiving it.
If the test leads are electrically connected, the corresponding value appears on the display. For a simple continuity check, you are also informed by a signal tone that current is flowing. You can easily perform this test by holding the two test probes together – then read the display of your ammeter to see which indication appears when current is flowing unhindered in the circuit. If no current is flowing, the display shows a “1” – some devices also show “OL”. (open loop) off. Now you can start troubleshooting.
To test the current passage, place the test prods at both ends of the circuit. Whether the current is direct or alternating current is irrelevant. (An exception is the measurement of diodes).
If your current tester has no continuity test function, you can still perform it: To do this, set the rotary switch on the front of the multimeter to the “Measure resistance” option, if necessary, the symbol Ω (ohm) will appear at this point. Set the smallest possible resistance measurement option. Your digital multimeter will now send a small amount of electrical current and measure whether it is also received at the other measuring tip. If the value shown in the display is very small or zero, you can assume that the current is flowing.
You can always check the functionality by holding the two measuring tips together. If your current tester does not detect any current flow, the display shows “1” or “OL”. (depending on the manufacturer).
To test a car battery, connect the test leads to your digital multimeter as described above. Set the rotary switch to DC, a straight line or a V (for volts) may also be shown at this point. Many current testers switch automatically between DC and AC.
If your multimeter does not have automatic detection, set the range of voltage you expect to see. If you select this value too low, you are protected by the internal overload protection and you will hear a warning tone. In this case, correct the manual value upwards.
For a successful voltage measurement, it is better to select a high value.
Now hold the red test lead to the positive pole of your battery or your circuit to be tested. Connect the black test lead to the respective negative pole. For example, if you use a 9-volt block as the test object, your digital multimeter should now show a value around 9 volts in the display. If you have reversed the two poles, you will see a negative value. Neither your circuit nor your multimeter will be damaged by an (accidental or intentional) reversal of the polarity. Only the value in the display is not correct.
For further examples of the proper use of your multimeter, please read the manual. There are also many interesting video tutorials on the Internet on the use of current multimeters. If necessary, look for instructions on temperature measurement or transistor testing with the multimeter.
