The home master periodically needs to measure the parameters of the circuits. Check what voltage is currently in the network, if the cable is frayed, etc. For these purposes, there are small devices - multimeters. With small size and cost, they allow you to measure various electrical parameters. Let's talk about how to use a multimeter.
External structure and functions
Recently, specialists and radio amateurs mainly use electronic models of multimeters. This does not mean that arrows are not used at all. They are indispensable when, due to strong interference, electronic ones simply do not work. But in most cases we are dealing with digital models.
There are different modifications of these measuring instruments with different measurement accuracy, different functionality. There are automatic multimeters in which the switch has only a few positions - they choose the nature of the measurement (voltage, resistance, current strength) and the device chooses the measurement limits itself. There are models that can be connected to a computer. They transfer measurement data directly to a computer, where they can be saved.
But most home masters use inexpensive models of the middle class of accuracy (with a 3.5 bit depth, which provides an accuracy of 1% readings). These are common multimeters dt 830, 831, 832, 833. 834, etc. The last digit shows the "freshness" of the modification. Later models have wider functionality, but for home use, these new features are not critical. Working with all these models is not much different, so we will talk in general about the techniques and procedures.
The structure of the electronic multimeter
Before using the multimeter, we will study its structure. Electronic models have a small LCD screen that displays the measurement results. There is a range switch below the screen. It rotates around its own axis. The part on which the red dot or arrow is applied indicates the current type and range of measurements. There are marks around the switch that indicate the type of measurements and their range.
Below on the body there are sockets for connecting probes. Depending on the model of sockets, there are two or three, there are always two probes. One positive (red), the second negative - black. The black probe is always connected to a connector labeled "COM" or COMMON, or which is labeled as "ground". Red - to one of the free nests. If there are always two connectors, there are no problems, if there are three sockets, you need to read the instructions for what measurements to insert the “positive” probe into which socket. In most cases, the red probe is connected to the middle socket. This is how most measurements are made. The top connector is necessary if you are going to measure a current of up to 10 A (if more, then also in the middle socket).
There are tester models in which the sockets are located not on the right, but at the bottom (for example, the Resant DT 181 multimeter or Hama 00081700 EM393 in the photo). There is no difference when connecting in this case: black to the socket with the inscription “COM”, and red according to the situation - when measuring currents up to 200 mA to 10 A - to the rightmost socket, in all other situations - to the middle one.
There are models with four connectors. In this case, there are two sockets for measuring current - one for microcurrents (less than 200 mA), the second for current strength from 200 mA to 10 A. Having understood what is in the device and why, you can begin to figure out how to use a multimeter.
Switch position
The measurement mode depends on the position of the switch. There is a dot on one of its ends, it is usually tinted with white or red. This end indicates the current mode of operation. In some models, the switch is made in the form of a truncated cone or has one pointed edge. This sharp edge is also a pointer. To make it easier to work, you can apply bright paint to this pointing edge. It can be nail polish or some kind of abrasion resistant paint.
By turning this switch you change the operating mode of the device. If it stands vertically upwards, the device is switched off. In addition, there are the following provisions:
- V with a wavy line or ACV (to the right of the "off" position) - AC voltage measurement mode;
- A with a straight line - DC current measurement;
- A with a wavy line - definition of alternating current (this mode is not available on all multimeters, it is not on the photos above);
- V with a straight line or the inscription DCV (to the left of the off position) - for measuring direct voltage;
- Ω - resistance measurement.
There are also provisions for determining the gain of transistors and determining the polarity of diodes. There may be others, but their purpose must be sought in the instructions for a particular device.
measurements
Using an electronic tester is convenient because you do not need to look for the desired scale, count the divisions, determining the readings. They will be displayed on the screen with an accuracy of two decimal places. If the measured value has polarity, the minus sign will also be displayed. If there is no minus, the measurement value is positive.
How to measure resistance with a multimeter
To measure the resistance, move the switch to the zone marked with the letter Ω. Choose any of the ranges. We apply one probe to one input, the second to the other. Those numbers that appear on the display are the resistance of the element you are measuring.
Sometimes the screen does not display numbers. If "jumped out" 0, then it is necessary to change the measurement range to a smaller one. If the words “ol” or “over” are displayed, it is “1”, the range is too small and must be increased. That's all the tricks of measuring resistance with a multimeter.
How to measure current
To select the measurement mode, you must first determine the current direct or alternating. There may be problems with measuring AC parameters - this mode is not available on all models. But the procedure, regardless of the type of current, is the same - only the position of the switch changes.
D.C
So, having decided on the type of current, we set the switch. Next, you need to decide which socket to connect the red probe to. If you don’t even know approximately what values \u200b\u200bto expect, so as not to accidentally burn the device, it is better to first install the probe in the upper (leftmost in other models) socket, which is signed “10 A”. If the readings are small - less than 200 mA, move the probe to the middle position.
The situation is exactly the same with the choice of the measurement range: first set the maximum range, if it turns out to be too large, switch to the next smaller one. So until you see the evidence.
To measure the current strength, the device must be included in the open circuit. The connection diagram is given in the figure. In this case, it is important to set the red probe to the “+” of the power source and touch the next circuit element with black. When measuring, do not forget that there is food in there, work carefully. Do not touch the bare ends of the probe or circuit elements with your hands.
Alternating current
You can try the AC measurement mode on any load connected to the household power supply and thus determine the current consumed. Since in this mode the device must be included in a circuit break, this may be difficult. You can, as in the photo below, make a special cord for measurements. There is a plug at one end of the cord, a socket at the other, cut one of the wires, attach two WAGO connectors to the ends. They are good because they also allow you to clamp the probes. After the measuring circuit is assembled, we proceed to the measurements.
Move the switch to the "alternating current" position, select the measurement limit. Please note that exceeding the limits may damage the device. In the best case, the fuse will burn out, in the worst case, the "stuffing" will be damaged. Therefore, we act according to the scheme proposed above: first we set the maximum limit, then we gradually reduce it. (do not forget about the rearrangement of the probes in the sockets).
Now everything is ready. First, connect the load to the outlet. Maybe a table lamp. We insert the plug into the network. Numbers appear on the screen. This will be the current consumed by the lamp. In the same way, you can measure the current consumption for any device.
Voltage measurement
The voltage can also be variable or constant, respectively, we select the required position. The approach to choosing a range is the same here: if you don’t know what to expect, set the maximum, gradually switching to a smaller scale. Do not forget to check whether the probes are connected correctly, in the right sockets.
In this case, the measuring device is connected in parallel. For example, you can measure the voltage of a battery or a conventional battery. We set the switch to the position of the DC voltage measurement mode, since we know the expected value, we select the appropriate scale. Next, with the probes, touch the battery on both sides. The numbers on the screen will be the voltage that this battery produces.
How to use a multimeter to measure AC voltage? Yes, exactly the same. Just choose the right measurement range.
Testing wires with a multimeter
This operation allows you to check the integrity of the wires. On the scale we find a continuity sign - a schematic representation of the sound (look at the photo, but there is a double mode, and maybe only a continuity sign). This image was chosen because if the wire is intact, the device makes a sound.
We put the switch in the desired position, the probes are connected as usual - in the lower and middle sockets. We touch one probe to one end of the conductor, the other to the other. If we hear a sound, the wire is intact. In general, as you can see, using a multimeter is easy. Everything is easy to remember.