Portable digital multimeters
(7)Digital multimeter is designed for digital measurement of direct current, variable and resistance voltages. Such a device can be used as an independent instrument or as a block of central data registration and processing system. Their potential and metrological parameters enable a wide range of applications in laboratory, workshop and industrial sectors.
The principle of operation and construction of a multimeter
The multimeter works by measuring direct current voltage. It converts the voltage value into a time value. Next, it digitally counts the measurement of pulses of a reference generator. While the voltage is being measured, the interfering voltages are averaged. This factor causes low sensitivity of the voltmeter to interference and noise during direct current voltage measurements. We can also calculate the resistance of a given element by measuring out voltage drop on the measured resistance. The multimeter is built to a large extent from integrated circuits. This solution ensures high reliability as well as small size and low power consumption of this tool.
How to choose a digital multimeter?
Particular types of multimeters differ in functions, ranges of measurements and screen resolutions displaying the results. Among them, we can distinguish two groups:
- multimeters with manual change of measuring ranges,
- multimeters with automatic change of measuring ranges,
The manual multimeter has a switch on which the range should be selected manually. It is a solution where we consciously predict what order of magnitude is going to be measured. This, on the other hand, allows us to choose an adequately larger measuring range. It is important not to increase the ranges during the measurement - it can lead to the firing of rotary switch contacts. The second type of digital multimeters is equipped with an automatic change of the measuring range. Before using this meter, it is necessary to set the appropriate position on the rotary switch, depending on what you want to measure. After setting the switch, we can connect the wires to the source which is being measured.
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