Getting Started Tutorial on Using a Digital Multimeter

The multimeter is one of the most commonly used instruments by radio enthusiasts and electronics enthusiasts. With the development of measurement technology, multimeters have evolved from the pointer display of the early mechanical meter to the current mainstream digital multimeter. Digital multimeters have the characteristics of convenient reading and high measurement resolution.

Digital multimeter battery installation

The digital multimeter is an electronic measuring instrument powered and driven by a battery. It can measure voltage, current, resistance and extended measurement of temperature, diode, capacitance, Frequency, transistor amplification, etc. all require battery power.

Traditional analog multimeters do not require battery support when measuring voltage and current. The internal battery is mainly used for resistor and transistor amplification (extended function). Generally, entry-level digital multimeters with low power consumption are powered by 9V laminated batteries, while mid-to-high-end products with larger power consumption are powered by multiple AA batteries (AA batteries).

The first step to start using a digital multimeter is to install a battery for the meter. Both 9V laminated batteries and AA batteries have polarity. There are obvious polarity installation prompts in the battery compartment of the multimeter, so you should pay attention to distinguish them when installing. The positive and negative poles of the 9V laminated battery use different snaps, which can effectively prevent incorrect battery polarity installation.

In view of the fact that some big-name batteries still have a certain chance of leaking after the power is exhausted, it is recommended that home amateur users who use the multimeter very rarely should take out the multimeter battery if they do not use the multimeter for a long time.

For commercial users or industrial users who use digital multimeters frequently, it is recommended to purchase a multimeter powered by AA batteries. Using rechargeable AA batteries can greatly reduce the average battery cost. . Although most digital multimeter instructions recommend the use of dry batteries, there is actually nothing wrong with using rechargeable batteries.

The meter rods and jacks of digital multimeters

Most digital multimeters have multiple jacks to connect to the meter pens. Usually there is only one black jack on the multimeter, which is connected to the black meter rod, which is the negative pole and "ground" /COM. There are multiple red jacks with different functions. They are connected to the red meter rod, which is the positive pole.

Develop a good habit when using a multimeter. The red meter rod is connected to the voltage measurement hole of the multimeter by default. Even if it is temporarily used to measure current, it should be restored to the voltage measurement connection mode immediately after the measurement is completed. There are two common materials for multimeter lead wires, one is cheaper plastic wire, and the other is better silicone wire.

The silicone wire can also keep the software soft at low temperatures and has better pressure resistance. The test leads of a multimeter are wearing parts, and many users will buy accessories. It is recommended that the test leads made of silicone wire from famous brands have better performance. For high-voltage measurement applications, the quality and performance of the test leads are directly related to the operator's personal safety and should not be taken lightly.

Basics of multimeter measurement

Multimeter gear setting

Digital multimeters come in two categories: manual gear and automatic range. The manual range multimeter looks like it has a wide range of ranges and can even compete with traditional analog multimeters. Users of this type of multimeter need to choose the measurement items and related ranges themselves. When using a manual-shift digital multimeter, care should be taken to select the correct measurement function and range.

The automatic range multimeter looks very simple and has very few gears. Each gear corresponds to a measurement item, and the specific range is automatically selected and matched by the multimeter. The technical difficulty of operating an automatic range multimeter is lower than that of a manual range multimeter. Users only need to select the measurement items (DC voltage, AC voltage, DC millivolt voltage, AC millivolt, resistance, DC current, AC current, etc.) to set it.

Multimeter voltage measurement

The equivalent structure of the digital multimeter voltage measurement circuit is in parallel, and there is no need to disassemble components. In a typical application, the red and black meter rods of the multimeter are touched separately to the object being measured. The pins on both sides of the component are enough. This is the most common application of multimeters.

The digital multimeter measures voltage into DC voltage and AC voltage. DC voltage is divided into positive pole and negative pole. Generally, the red meter rod of the multimeter is in contact with the positive pole, and the black meter rod is in contact with the negative pole or "ground".

The digital multimeter can display negative voltage values. At this time, if the measured point is not a negative voltage, then the positive and negative polarities of the meter rod touching the DC voltage point are reversed. A digital multimeter showing negative voltage will not cause damage to the instrument. There is an empirical connection method in daily circuit board and circuit testing. Reliably connect the black meter rod of the multimeter to the public "ground" of the circuit board. In this way, you only need to focus on holding the red meter rod with one hand to measure the voltage at each point.

When the internal resistance of the digital multimeter for voltage measurement is high, falsely high voltage may occur when measuring an open-circuit battery. During actual measurement, connecting a certain load in parallel to both ends of the battery and then measuring the voltage can avoid the problem of falsely high battery voltage. The "low internal resistance measurement function" provided by some new digital multimeters is based on the above principle.

When measuring a high voltage higher than the safe voltage, your hand can only touch the part with the insulating sheath of the meter rod, and never touch the exposed metal part of the front end of the meter rod. Users engaged in high-voltage measurement should stop using the test leads immediately if they find that the test leads are damaged.

Use a multimeter to measure and repair the switching power supply. It is best to install an isolation transformer on the mains side of the switching power supply to ensure safety. The so-called isolation transformer is a 1:1 transformer. Its function is to prevent the load from having a direct path with the mains and reduce the risk of electric shock.

Multimeter current measurement

The equivalent structure of the current measured by the digital multimeter is series connection. It is necessary to disassemble the components or disconnect the original circuit and connect the multimeter in series to the circuit. The front end of the multimeter's meter rod is a probe type. In order to stabilize the series connection such as circuit, you can use accessories such as alligator clip kits. The digital multimeter has a dedicated socket for measuring current. Before measuring the current, the user first selects the appropriate current measurement range, and then inserts the red meter rod plug into the current measurement hole on the multimeter.

Multimeter current test circuits are generally equipped with fuses, which can break the circuit in time when overcurrent occurs to ensure the safety of the multimeter and operators. Most mid- to low-end digital multimeters use glass tube fuses. It is recommended to use fast-acting fuses when replacing them. During the measurement process, if the current indication is always zero or the circuit is blocked, it is recommended to first check whether the current fuse of the multimeter is blown.

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