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As with all the other measuring instruments, it is necessary first to clarify which application the meter is to be used for. Will it be daily used in tough industrial environments or applied in crafts and handiwork? Should it be used for training purposes in education? Or is it required for practicing some hobby? After this fundamental question has been answered, you are already one step forward. Now you can already directly deal with the multimeters and look in the assortment of our products, how the multimeter should display the measured values.
Analog or digital multimeter?
Analog Multimeters barely find application in daily use. Reading the right scale, choosing the right measuring range is not as easy as in a digital multimeter. Nevertheless, analog multimeters still have the right to exist. So it is advisable to use an analog multimeter in training or for demonstration purposes. This kind of a multimeter has an advantage that you can show and see how the measured value moves in the measuring range. It gives the user a better feel concerning the measured variable. For this reason, we recommend an analog multimeter for training and demonstration purposes.
A digital multimeter as against to the analog multimeter offers an advantage that much more features and functions may be added to the device. So, these multimeters can also measure other physical variables, such as temperature. Likewise, digital multimeter can be equipped with memory and interface. A digital multimeter displays the reading on a LC or OLED display. Here the indication of the digits is a measure of the resolution of the digital multimeter. Just what is a digit? Digit comes from English and means simply number or numeral. Thus, this means, for choosing a multimeter, that the higher the indication of the digits, the higher the measured values can be resolved. In this context it is often written that a multimeter has a 3 ½ digit display or a 4 ½ digit display. This means exactly: The multimeter has got 3 full digits available to display a measured value. So, the multimeter can fully represent 999. Then there is also a half-digit on the screen. This is always the first number on the display. This can then often be only a “1” or a negative sign. It follows that a multimeter with a 3 ½ digit display can display a maximum of 1999 or -999. For further explanation the following graphic is presented:
In addition to the numerical display of the measured values digital multimeters have got a bar graph on the display. This digital bar graph is similar to a scale in an analog multimeter. The graph helps the users of the multimeter to estimate the measured value in the measuring range.
Besides the typical measurement functions such as voltage and current, resistance, capacitance, etc. many multimeters have a diode test and semiconductor test, a non-contact voltage detection, temperature measurement, etc. This turns the multimeter into a universal tester in industry and crafts.
In multimeters one may often find a specification RMS or TRMS (or True RMS) which means that at a non-sinusoidal AC the signal is properly measured and displayed on the screen of the multimeter. Here it should be noted that the multimeters work in different frequency spectra. Common bandwidths for TRMS measurements of current and voltage are 10 kHz or 100 kHz.
Common multimeters have a current measuring range of 10 A. In order to measure the higher AC or DC currents, you have to use an external current probe for multimeter. These current transformers can measure up to several thousand amperes indirectly. As an output signal these transformers provide a voltage signal, and this may be mV per A. Now it can be relatively easy to determine via the current measurement function the current, which flows in the conductor.
The safety of multimeters should not be left without attention and entirely aside. For that the multimeters are divided into safety categories. The left graphic provides information on the safety categories and the scope of application.
Multimeters are divided into two groups: multimeter and analog multimeter. This article details the features of a digital multimeter. Devices with an analog display can be found in the article “Analog Multimeter”. The multimeter is a measuring device that combines different measuring types and ranges in one device. In the majority of application cases, the meter is used as a voltage or current measuring device. In addition to these two primary measuring functions for DC and AC variables, with the modern multimeters it is possible to accurately measure resistance, capacitors, diodes, coils.
The advantages of digital multimeters are a relatively simple mechanical construction and mass-produced electronic components, which makes them relatively inexpensive. The development of modern LC displays allowed the improvement of the handling of multimeters. Thus, depending on the set measured variables and the selected measuring range, the SI unit and the measured value are displayed as a number and in a bar graph. It also has protection circuits against overload and reverse polarity. Impacts and shocks cannot influence them much, since no moving parts can be damaged. Comfortable devices can automatically select the voltage range. Digital multimeters are powered by a battery, power supply or solar cell.
In a digital multimeter, the signal is measured electronically with an analogue-to-digital converter and the value is displayed as a numerical value. Usually the measuring ranges are from 200 mV to 1000 V and from 20 μA to 20 A. In the voltage measurement, they usually show rather high internal resistance of 1 to 20 MO, with the standard of 10 MO. Depending on the measuring range, the relative error limit is less than 1%. For a higher-quality multimeter, it is less than 0.2% in the DC voltage ranges. In the switchable shunt resistors, the current measurement is carried out by the voltage measurement. The resistance is also measured by voltage at a switchable constant current source.
Some devices have additional measurement possibilities for frequencies, capacitances, inductances, as well as transistor and diode characteristics. Thanks to built-in sensors, sound, light intensity, humidity and temperature measurements can also be made. The possibilities of multimeter application can be further increased by external sensors, which, for example, have voltage outputs. For humidity, sound, light or temperature measurement, there are further measuring possibilities for speed, pressure, air speed, and current (via a transducer clamp).
In an analogue miltimeter, the measured value is displayed on a pointer measuring device for different measuring ranges with several scales. The values are displayed by graduations, intermediate values can be calculated. The error limits for these devices may well be less than one percent of the measuring range end value (for the high-quality ones).
The decisive factor is usually a moving-coil meter. The measuring ranges of the moving-coil units at DC voltages are from 100 mV to 1000 V, for DC currents from 100 μA to 10 A. High-quality devices sometimes demonstrate even smaller ranges. When measuring voltage, analogue multimeters usually show a much lower internal resistance than digital multimeters. This, at the presence of high-impedance voltage sources, can lead to measuring deviations (circuit influence). Built-in amplifiers reduce the influence of internal resistance during current and voltage measurements. This should allow analogue multimeters to achieve a higher internal resistance (which can correspond to one of the digital multimeters).
During the resistance measurements, the current, that a built-in battery can let flow through the resistor, is calculated. The measurement is only suitable for rough statements, since the ratio is strongly nonlinear. In very high-quality devices, during the resistance measurements, an amplifier electronics for scale linearization can be used.
Types of multimeters
The multimeters are offered in different forms and types. Handheld devices are mostly presented in the classic form with a display in the upper part, the multi-function rotary switch in the middle part and the test line jacks in the lower part of the device. These multimeters are often used by maintenance personnel as a universal measuring device.
Desktop or laboratory multimeters are used at stationary workstations. They usually have larger displays and can be supplied with 230 V AC. Pen multimeter or voltage tester with multimeter function is used by craftsmen performing small measuring tasks. The other categories present amperemeter pliers / or also oscilloscopes with multimeter function. On most units the measuring range selection is set automatically or the measuring range is selected manually.