A multimeter is – in simple terms – an ammeter. Not only as a hobby electrician, but you also benefit from the digital multimeters presented here in your work with electricity. High-quality multi-function current testers make it easier for you to work on the construction site, in scientific research, and in electrical companies. In addition to professional current controllers, we present variants that are ideal for use in the hobby sector.
Inform yourself in the guide about the functionality and optimal use of modern digital multimeters. The handy measuring devices are available in different sizes and versions. If required, many models can be easily transported in the jacket pocket or have holding clips for the belt.
Top 10 Multimeters
Structure, components, and mode of operation of digital multimeters
A DMM (Digital Multimeter) is an electronic meter for electricity. It displays the measured values clearly as a numeric value in the display. You can carry out a variety of current tests with it. Even cheap instruments for hobby use measure the default values of electrical voltage, electrical current and ohmic resistance. This is usually also possible in DC circuits as in AC (AC or DC). High-quality professional current testers have additional options and continue to measure:
- The electrical capacity
- The inductance of components
- The temperature
- The frequency of the flowing current
For continuity measurements, an acoustic signal is usually available. In a digital multimeter, the signals are recognized by an analog-to-digital converter and displayed as a numeric value in the display. This is usually illuminated, the numbers are displayed very largely. This allows you to quickly record the measured values, even without bringing 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.
By manufacturer, some digital current controllers may deviate from these values and limit the measurement space. The built-in high internal resistance of a digital multimeter is generally between 1 and 20 MΩ, most ammeters have a resistance of 10 MΩ.
Current measurement with a modern digital multimeter
To test the current intensity, the device measures the voltage via a switchable shunt resistor. It is a term from the electrical engineering, which is also referred to as current measuring resistor or shunt resistance. This electrical resistance is low impedance and is used to measure electric current.
When current flows through the shunt, it causes a voltage drop proportional to its magnitude. This voltage drop is measured by the digital multimeter, converted to a readable value and displayed on the display. Many devices have a data-hold feature that lets you easily store measurement results.
Resistances measure with a digital multimeter
Even with a resistance measurement, the device detects the voltage that prevails in the circuit under test. The measured values in the display are calculated by the device on the basis of a constant current source. It can be assumed that within an electrical circuit, a constant electric current flows, which is constant regardless of the electrical voltage at the connection points at all points of the circuit.
Where can you use digital multimeters?
Use your compact current tester wherever you want to check an electrical circuit. Many gauges also work contactless so you can check the cabling in the wall. Common applications for True-RMS multimeters are:
- Electrical engineering as a hobby
- Electrician at work
- A standard tool in electrical companies
- School and University (Research)
What is DC? What is AC?
- Direct current
DC current flows constantly in the same direction, also the strength does not change. Frequently colloquially DC and DC are confused with each other, with DC sources produce a DC in the circuit.
By means of special mechanisms, direct current can be generated from alternating current. For this purpose, only so-called “rectifiers” are needed, which are built into the electrical circuit. Most electronic home appliances, such as computers, radios or TVs, use DC power for proper operation. However, the socket in the wall outputs AC power. The necessary rectifiers can be installed directly in the electrical appliance, but usually, an adapter or corresponding power supply is used, which converts the power.
- Alternating current
With alternating current, the direction, also called polarity, constantly changes in regular repetitions. The positive and the negative instantaneous values complement each other in such a way that the current is equal to zero in terms of time. If direct current and alternating current occur together in an electrical circuit, this is called mixed current. More AC power than DC 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.
On high-frequency alternating current is used mainly in the field of electromedicine and also in telecommunications.
If you want to charge a sensitive device, such as a smartphone, to a gasoline power generator, the generated power must be converted in any case. If this does not happen, the electronic device is likely to break down and can not be repaired due to the heavy overload in the electronic components.
Tutorial: Instructions for Using Digital Multimeters
With a portable power tester, you can easily see if any elements of your circuit are electrically connected. This is the so-called continuity test. On some devices, you will also receive visual and audible confirmation when the electrical current is flowing freely. For most multimeters, you will hear a distinct beep if the circuit under test is not live.
In this case, stop the measurement and check all components for defects (eg cable breakage), check all solder joints for their quality and check the fuses. After troubleshooting, a repeated current check can be performed to inform you of the success and progress of your repair.
Now switch on your multimeter and use the rotary switch to select the respective setting, for example, continuity test. For most digital multimeters, a symbol that looks like a wave is shown here. Please refer to the details of the labeling of your current tester in the enclosed operating instructions as there may be variations in the representation between the various manufacturers.
Above all, 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 warns you with a signal tone.
Multimeter manual for voltage measurement on a battery
Connect the test leads to your digital multimeter as described above. Set the rotary switch to DC, it may also have a straight line or a V (for volts) at this point. Many power testers automatically switch between DC and AC power, and at home, all home appliances are always DC powered.
If your multimeter does not have automatic detection, set the range of voltage that you expect. If you select this value too low, you are protected by the internal overload protection and hear a warning tone. In this case, correct the manual value upwards.
Now hold the red test lead to the positive pole of your battery or the circuit under test. Connect the black test lead to the respective negative pole. For example, if you take a 9-volt block as the examination object, your digital multimeter should now display a value around 9 volts in the display. If you have swapped the two poles, you will see a negative value. An (accidental or intentional) reverse polarity will not damage your circuit or your multimeter. Only the value in the display is not correct.