Components of the digital meter
We immediately begin to get acquainted with the various components of the digital meter, in order to get to know the instrument in depth: it is an essential step to learn how to use it properly during measurements. The most popular format is that of digital handheld multimeter, basically consisting of a portable body in which the following elements are distinguished:
- Display - it is the component where the measurement values are displayed (more sophisticated testers could also show additional information): in standard devices it has 4 digits, with the possibility of displaying an additional negative sign. In most devices the screen is LED or LCD and can have backlight for better consultation in low light conditions.
- Selector - this is the main command of the instrument: it is used to select the measurement mode, for example current (THE), tension (V) e resistance (Ω) and set the relative scale of values. In most devices it consists of a simple one knob, but in some more advanced models there may be a keypad.
- buttons - depending on the model, that of power on of the device and some additional functions that can be activated using specific buttons, such as the one for backlight or the one named Hold for the measurement lock on the display.
- Connectors - are used to insert the test leads to connect the electrical circuits to the tester. Also in this case, depending on the model, there may be more entrances: as a base you will certainly have the door available COM to which the black lead dedicated to earth is conventionally connected, while the one bearing the wording mAVΩ is intended for the red probe and is comprehensive of the functionality of voltmeter, ohmmeter e ammeter (in some cases, however, the tester may have separate ports for each function). Another very useful connector is the one called 10ADC (sometimes identified with 10A), used for current measurements above 200mA.
- Battery compartment - usually placed on the back of the device, it is used to house the batteries essential for the correct functioning of the tester.
To carry out the measurements are also supplied with the tester tips, that is the probes connected to a pair of red and black cables that terminate at the other end with two circular connectors covered with plastic, which in turn must be inserted in the respective ports of the multimeter.
Functions of a digital meter
There are many functions of a digital meter that you can use to diagnose, for example, the operation of an electrical circuit, or simply to check the residual voltage of a battery.
The most common, for which I will explain the measurement method to you later, are those relating to the verification of the following values.
- Voltage - could be read more (DCV), and is indicated in the selector with the symbol V- volts (for measuring, for example, the charge in batteries) or alternating (the symbol, in this case, is formed by the letter V followed by the tilde ~) which, that is, varies over time (as in the case of power supply from a generator)
- Resistance - if you need to check the resistance of an electrical device, you will need to refer to the quantities included in the section marked with theohm, or [Ω].
- Current - also in this case it is possible to measure both that read more (DC) than that alternating (AC): you will find the scale of values available under the letter [A] in the selector. As for alternating current, however, you should know that many inexpensive testers do not support this type of measurement.
More advanced multimeters, in addition to providing a more precise measurement, may have additional features such as those for the analysis of frequency, capacity, temperature, just to name a few examples intended for a more professional use of the instrument. Many devices also integrate a diodes and l 'oscilloscope.
How the digital tester works
After this essential overview of the device and the basic features it has, it's time to understand how the digital tester works: In the next chapters I will show you how to correctly perform a measurement of continuous voltageand resistance and direct current, which represent the most common uses in the professional and non-professional fields.
In which cases you might need the voltage measurement through your multimeter? The tension, as you may already know, corresponds to the energy needed for move a unitary electric charge from one point to a point b: the pressure that is exerted allows the charged electrons to pass through a conduction circuit and therefore to carry out their work, such as the illumination of a lamp.
It is measured in volt: the battery, from this point of view, represents a striking example of a conductor in which, through a chemical process, the transport of a certain amount of energy is favored to allow the powering of a device.
The procedure to follow to test the charge of a battery using the multimeter is very simple: first you need to insert the connector of the black test lead into the port COM and the red probe in that mAVΩ (or, if present, in the dedicated one with the symbol [V]). Subsequently, the tester must be turned on using the appropriate button On / Off (or by directly selecting the required value from the knob).
The selected value must be higher (but as close as possible) to that indicated in the specifications of the device on which the measurement is being made: if, for example, you want to check the charge of a 1,5V AAA stylus, select the parameter 2V using the knob.
Now connect the tip of the black cable to the ground of the battery (so to speak, from the side with the symbol [-] ), then make sure that the tip of the red cable touches the power supply (symbol [+]): the display will immediately show the remaining battery charge.
resistance we mean the ability of a body to oppose the passage of electric current. It may therefore be useful to perform a resistance measurement to determine the condition of the components that are part of the circuit: over time, in fact, wear can lead to a degradation of this capacity.
The higher the value obtained (expressed in ohm), the lower the current flow able to pass this component: the operation of the device in which it is integrated could be compromised if the test shows the presence of high resistance values.
As a first rule, it is important that the circuit you are going to diagnose is disconnected from the mains and is not, therefore, fed in any way. Secondly, it should be noted that ideally the component to be tested would go removed from the circuit, to prevent the measurement from being affected by the presence of other components.
Finally, as a last precaution, it is important that, during the test, the hands do not touch the test leads: the human body would cause a decrease in resistance, causing the multimeter to record unreal values.
So let's see how to perform this measurement on a resistor, or that component that, within a circuit, has the specific purpose of opposing electrical resistance to the passage of current, for example to limit the current destined for certain sectors that need fewer resources, such as LED.
The connection to be made is the same as seen in the chapter dedicated to voltage: the connector of the black cable must be inserted into the port COM, the red cable connector into the port mAVΩ (or on the one dedicated to the ohmmeter, if available separately, identified with the symbol Ω).
After turning on the tester, if you have no idea what the resistance range might be, it is a good idea select the highest value within the ohm scale (e.g. 2M), unless a button is present autorange, which automatically determines the scale based on the recorded values.
The multimeter will immediately show the value OL, before you even connect the test leads to the component. At the same time you may notice the presence of the symbol MΩ on the display, as in this phase (with the test leads still not in contact) the resistance encountered is very high.
Now you just have to make contact between the leads and the metal ends of the resistor: if the tester shows a result equal to 0, you need to scale the reference value to the next one with the knob, and so on, until you get a consistent result.
Current measurement takes place on the scale of ampere, identified by the symbol [AND]. The procedure to follow, in this case, is very different from those of resistance and tension (which occurs in parallel): I advise you to proceed only if you feel confident about this type of activity, which involves the use of direct current flows.
Basically, to obtain the real values of the flow of electrons passing through a given circuit, it is necessary physically interrupt him at any point and make the component of ammeter of the tester becomes itself part of the circuit, feeding the current to the next point.
The multimeter, therefore, must be connected by inserting the connector of the black cable into the port COM and the test lead to the wire coming out of the circuit. The connector of the red cable, on the other hand, must be inserted into the port mAVΩ (or, if present, in the dedicated door with the symbol [AND]) to which the fuse from 200/250 mA, while the relative tip is in contact with the input cable to the circuit (see diagram above for more details). Note: if you are in doubt that the circuit can use more than 200mA, it is advisable to move the red probe on the port from 10A, which is connected to a fuse capable of carrying a greater load.
In addition, it is good to know that for this type of measurement your own must be monitored evolution over time, at least for a few seconds: it could be useful, therefore, to equip yourself with two metal clamps able to hold the wires that allow the current to exit the circuit in series and its subsequent re-entry, thus freeing the hands.
After accessing the tester, it also activates the circuit: I suggest you select the maximum scale value in amperes, available on your multimeter and to decrease it according to the consistency of the detected data. The display will show the instantaneous current reading in DC mode which, according to the conditions of use of the circuit, will vary from time to time.How to use digital tester