How to use the multimeter?

A multimeter, also known as a three-way meter, and a multiplexing meter, is a multi-function, multi-range measuring instrument. Generally, a multimeter can measure DC, DC voltage, AC voltage, resistance, audio level, etc. Some can also measure AC, capacitance, inductance, and some parameters of semiconductors. It is a practical and straightforward measuring instrument. Today’s most commonly used multimeters are digital, and pointer multimeters are rarely used. Digital multimeters are relatively simple measuring instruments. A multi-purpose electronic measuring instrument generally includes an ammeter, voltmeter, ohmmeter, etc. It is sometimes called a multimeter or three-meter. Can use The multimeter can result in a wide range. The following will tell you the primary method of using the multimeter.

How to use the multimeter?
How to use the multimeter?

Precautions for the use of the multimeter

(1) Before using the multimeter, “mechanical zero adjustments” should be performed first; when there is no electricity to be measured, make the pointer of the multimeter point to the position of zero voltage or zero current.

(2) In the process of using the multimeter, do not touch the metal part of the test pen with your hands, which can ensure the accuracy of the measurement on the one hand and personal safety on the other hand.

(3) When measuring a certain amount of electricity, it is impossible to change gears while measuring, especially when measuring high voltage or large current, should pay more attention. Otherwise, the multimeter will be destroyed. If you need to change gears, you should disconnect the test leads first and then measure after changing gears.

(4) When using the multimeter, place it horizontally to avoid errors. At the same time, pay attention to prevent the influence of the external magnetic field on the multimeter.

(5) After the multimeter is used, the transfer switch should be set to the maximum block of AC voltage. If it is not used for a long time, it should also take out the battery inside the multimeter to prevent the battery from corroding other devices in the meter.

When using an analog multimeter, insert one end of the two measuring probes into the measuring end according to the requirements of red to positive (+) and black to negative (-), and then confirm whether the pointer is at the “0” position. The information should line up with the end line on the left side of the dial; if not, make a zero adjustment. Before measuring the current and voltage, the first estimate the range of the current and voltage to be measured first set it in a larger gear, and then adjust it to appropriate equipment to avoid excessive current from burning out the multimeter.

When making measurements, one should consider the influence of the multimeter’s internal resistance. For example, the test leads should be connected to the circuit under test to measure the voltage. The opposition in the multimeter also flows through the current, which influences the measured value. When calculating the voltage of the same point, if different gears are used, the internal resistance of the multimeter will be additional, and the degree of influence will also be other.

When measuring electronic circuits of transistors, it is better to choose the internal resistance of 20kΩ/V in DC mode, and this value is usually marked on the multimeter’s dial. In addition, transistor circuits often need to measure low-value voltages, such as 0.1V. At this time, the selected multimeter should have a measurement range of 1V.

How to use a multimeter
How to use a multimeter?

The use of the ohm block

1. Select the appropriate magnification. When measuring resistance with an ohmmeter, a correct magnification should be selected so that the pointer indicates near the median value. It is best not to use the left third of the scale, which is poorly dense.

2. Zero adjustments before use.

Three, can not live measurement.

4. The resistance under test cannot have parallel branches.

5. When measuring the equivalent resistance of polar components such as transistors and electrolytic capacitors, you must pay attention to the polarities of the two pens.

6. When measuring the equivalent resistance of the nonlinear element with the ohm stop of different magnifications of the multimeter, the estimated resistance value is not the same because each gear’s median resistance and full-scale current are extra. In a mechanical watch, the smaller the magnification, the smaller the measured resistance.

The use of the diode block

First, let’s learn the most straightforward diode gear, turn the knob of the multimeter to the position where the diode identifier is located. And then short-circuit the two test leads; you will hear the buzzer sound, which means that you can use the gear usually. In addition, it can determine that the resistance between the two test leads is zero. It is often used in life to measure whether there is an open circuit in the circuit and whether the devices are electrically connected. Since this file is a diode file, we can use this file to measure diodes. Voltage drop, when measuring, put the red test lead on the anode of the diode. The black test lead on the cathode of the diode can directly display the voltage drop value on the display screen. This file can also judge whether the diode is a silicon tube or a germanium tube and whether the diode is damaged.

The use of resistance files

Clockwise from the diode gear, you can see the resistance gear. There is an Ω symbol, which means the resistance gear is measured. When measuring, we should first judge the size of the selected resistance and then choose the knob to select the range. If you do not know the size of the opposition, you can Select a middle gear to try to measure and then change the equipment according to the estimated value of the measurement. We choose 1K resistance for testing, so change the pointer to 2K gear and then read the value directly on display. As for the needle part, because there is no positive or negative resistance, the red and black test pens can be connected to both sides of the opposition (do not touch the test pens when measuring large resistances), regardless of positive and negative.

Use of the triode file

Rotate the knob clockwise to reach the have gear. This gear is the gear for measuring the amplification parameters of the triode. Generally, there are two kinds of jacks, one is NPN, and the other is PNP. Before measuring, we must distinguish it clearly. Is it an NPN type transistor or a PNP type transistor? We use the NPN type here because the transistor has three pins, and the function of each pin is different, so after we distinguish the pins, insert them into the correct pin name according to the pin name. The measuring jack can directly read out the magnification of the triode on display.

Use of the voltage gear

Rotate the measuring knob again; the next gear is the voltage gear. In this multimeter, both the AC gear and the DC gear are in this range, so before measuring, we should first determine whether the voltage we are measuring is AC or DC. To change the measurement type, you can press the AC/DC switchgear (the multimeter’s DC/AC conversion gear, some multimeters are separate from DC and AC, this one does not have a gear change button). And select the appropriate range if I don’t know what the voltage to be measured is before the measurement. At this time, we must choose the gear with the most extensive range. Our standard AC is the AC used in the family, and the voltage is 220v. The typical DC is the output voltage of our computer’s USB socket, as an example, which is DC. 5v.

The use of the frequency meter

Rotate clockwise, and the next step is to measure the frequency. The dial is 10MHz, indicating that the maximum measurement frequency is 10KHz. When measuring, connect the test lead to both ends of the frequency meter, and the measured value can be directly read on display. The test lead should be linked correctly. Should be connected the red test lead to the positive terminal of the signal source, and the negative terminal should be connected to the negative terminal of the signal source.

The use of capacitor files

Sometimes we also use a multimeter to measure the capacitance. The first step is to determine the size of the capacitance and select the multimeter range. After selection, put the test leads on both ends of the capacitor without dividing the positive and negative poles. A polar capacitance can be measured directly without distinction if it is a polar capacitance. Positive and negative, you can now read the capacitance at this time on the display screen. In addition, it should note that when measuring capacitance, you need to insert the red test lead into the jack marked mA and can only calculate the result on this jack.

Tips for measuring DC with a multimeter

1. Carry out mechanical zero adjustments.

2. Select the appropriate range gear.

3. When using the current block of the multimeter to measure the present, the multimeter should be connected in series in the quilting circuit because only the series connection can make the current flowing through the ammeter to be the same as the current of the branch under test. When measuring, disconnect the unit under test and connect the red and black test leads of the multimeter in series between the two disconnected points. In particular, it should note that it cannot touch the ammeter in parallel in the quilt test circuit, it is hazardous, and it is straightforward to burn the multimeter.

4. Pay attention to the polarity of the measured electricity.

5. Correct use of scales and readings.

6. When the 2.5A block of DC is selected, the red test lead of the multimeter should be inserted into the 2.5A measurement jack, and the range switch can be placed on any range of the DC block.

7. If the DC measured by the quilt is more significant than 2.5A, the 2.5A gear can be extended to 5A gear. The method is straightforward; the user can connect a 0.24-ohm resistor between the “2.5A” jack and the black test pen jack so that the bag becomes a 5A current gear. The connected 0.24A resistor should be a wire-wound resistor of more than 2W. If the power is too small, it will burn out.

The current multimeters are divided into pointer type and digital type. They have their advantages. It is difficult to say who is good and who is terrible. It is best to have one pointer and one digital type. Amateur electronic production has an analog MF30 multimeter, a classic model. There are also veteran-level MF500 and cheap MF50 multimeters, which are generally available in telecommunications stores.

The three primary functions are to measure resistance, voltage, and current, so the seniors call it a three-meter. Today’s multimeters have added many new parts, especially digital multimeters, such as measuring capacitance value, triode magnification, diode voltage drop, etc. A talking digital multimeter can also broadcast the measurement results in language. (Actually, it’s not tricky; Bitbaby once wanted to make one with a microcontroller and a voice circuit 🙂

There are also many classic models of digital multimeters, such as DT830C, DT830C, DT890D, etc. The suffix at the back indicates the difference in function. Among them, DT830C has been bought for more than 30 yuan, which is cheap enough. But the baby installed an MF50 multimeter in school. The circuit principle is not complicated, but many components are not fixed on the printed board but are directly soldered on the wiring board. It is a bit troublesome for beginners to install it by themselves.

use a multimeter
use a multimeter

The most prominent feature of the multimeter is that it has a range switch, and this switch switches each function. A- represents the DC measurement, and the milliampere and ampere files are generally divided into several. V- means to measure DC voltage, the multimeter of the advanced point has millivolt gear, and the voltage gear is also divided into several bags. V~ is used to measure AC voltage. A~ measure the alternating current, and the resistance is measured in the Ω ohm range. A zero adjustment is required for an analog multimeter every time the resistance range is changed. Zero adjustments are to put the red test lead and black test lead of the multimeter together and then turn the zero adjustment button to make the pointer point to the zero position. To measure the current amplification factor of the triode, as long as the three pins of the triode are inserted into the corresponding holes on the universal panel, the have value can be measured. Note that PNP and NPN are different.

The following takes the MF30 multimeter as an example to illustrate the multimeter’s reading. The first scale line is the resistance value indication, the left end is infinity, the right end is zero, and the scale is uneven in the middle. There are R×1, R×10, R×100, R×1K, R×10K resistance gears, which respectively indicate the multiples of the scale indication and then multiplied to get the actual resistance value (unit is ohm).

For example, use the R×100 gear to measure resistance, and the pointer indicates “10”, then its resistance value is 10×100=1000, that is, 1K. The second scale line is shared by 500V gear and 500mA gear. It should note that the indication principle of voltage gear and current equipment is different from that of resistance gear. For example, 5V load means that this gear can only measure voltages below 5V, and 500mA gear can only measure 500mA. If the following current exceeds the range, it will damage the multimeter.

Note: The multimeter should be placed when used. The red test lead is inserted into the + hole, and the black test lead is inserted into the – spot. Use the current gear to test the present instead of the voltage gear and electrical block, which is valid for others. If you don’t know the range in advance, use the maximum range to measure, disconnect the measurement circuit, and change the gear. Never change the field under the condition of online. If the needle is deflected to the end quickly, the course should be disconnected immediately and checked.

Finally, there is a rule, that is, after the multimeter is used up, it is agreed that the range switch should be set to the highest level of AC voltage to prevent others from accidentally measuring the 220V mains voltage and damage. Remember the fine traditions left by the elders!

A multimeter is an instrument used to measure AC and DC voltage, resistance, DC, etc. An essential tool for electricians and radio production. At first glance, the multimeter is very complicated. It is composed of an ammeter (commonly known as a meter head), a dial, a range selection switch, a test pen, etc., as shown in Figure 1. When in use, if the range selection switch is pointed to the DC range, the ammeter M is connected with some shunt resistors to expand the range (Rg is the meter resistance), making it an ammeter with several degrees of different sizes. The measurement result depends on the DC scale on the dial to read. Usually, the second row on the dial is the current scale, as shown in Figure 2.

Similarly, suppose the range selection switch points to the DC voltage range. In that case, the meter head is connected with other resistors (such as R2, R3, and the principle of voltage division by series resistors is used to make it a multi-range voltmeter, as shown in Figure 3. The reading depends on a DC voltage scale on the dial. Most multimeters share a scale for voltage and current. If a rectifier is connected to the circuit for measuring DC voltage, it can measure AC voltage. The principle of measuring resistance is similar to measuring DC voltage, but it is just a test. It is necessary to add a set of batteries. When the selector switch points to the resistance range, you can find the first line of resistance-specific scale readings on the dial. There are many models of multimeters, but the primary usage is the same.

Take the MF30 multimeter as an example to introduce its usage. Preparation before use

First, before using the multimeter, you must be familiar with the function of the range selection switch. What exactly do you want to measure? How to test? Then turn the range selection switch to the position where the test file is required. Don’t get the gear wrong. For example, when measuring the voltage, when the selector switch is set to the current or resistance equipment by mistake, it is easy to burn the meter head.

Second, observe whether the pointer points to zero before use. Suppose you do not refer to the zero position. In that case, you can use a screwdriver to adjust the mechanical zero adjustment screw on the watch head to make the watch hand return to zero (generally, it is unnecessary to change it every time). The red test lead should be inserted into the positive socket, and the black test lead should be inserted into the negative socket.

To measure the voltage, align the tip of the range selector switch within the five-step range marked with V. If measuring AC voltage, it should point to V., And so on; if you want to change the resistance, the switch should file to the range. The measured current should point to mA or UA. Example 1 measures the voltage of a dry cell; see Figure 4.

When measuring the voltage, connect the meter leads to the circuit under test in parallel. According to the approximate value of the course under test, select a suitable range position. The maximum value of each dry cell is 1.5V, so we can place it in the 5V range. At this time, should read the 500 of the full-scale reading of the needle on the panel as 5. That is 100 times smaller. If the arrow points at the 300 mark, it reads 3V. Note that the index value indicated by the tip of the range switch is the corresponding value of the full-scale reading of the needle on the meter head. You can read the actual value when reading the meter as long as it is converted accordingly. Except for the resistance gear, all gears of the range switch read the measurement results in this way. In the actual measurement, when cannot determine the approximate value of the measured voltage, can turn the switch to the maximum range first. Then can reduce the content to the appropriate position. When measuring DC voltage, you should pay attention to the positive and negative polarities. Suppose you don’t know the positive and negative polarity of the circuit. In that case, you can put the range of the Wantian meter on the top gear, quickly try it on the course under test, and see how the pen needle is deflected can judge the positive and negative polarity.

Example 2, measure 220V alternating current. Turn the range switch to AC 500V. At this time, the full scale is 500V, and the reading is read according to the scale of 1:1. Insert the two test pens into the power supply socket, and the pointer at the scale points the measured voltage value. When measuring AC voltage, there is no positive or negative test lead.

1. Selection of pointer table and digital table

1. The reading accuracy of the pointer table is poor. Still, the process of the pointer swing is relatively intuitive, and the amplitude of the swing speed can sometimes reflect the measured size objectively (such as the slight fluctuation of the TV data bus (SDL) when transmitting data). Jitter); the digital meter reads intuitively, but the digital change process looks messy and not easy to watch.

2. There are generally two batteries in the pointer watch; one is low voltage 1.5V, and the other is high voltage 9V or 15V. The black test pen is the positive end of the red test pen. Digital meters usually use a 6V or 9V battery. In the resistance mode, the output current of the test pen of the pointer meter is much larger than that of the digital meter. Using the R×1Ω file can make the speaker emit a loud “click” sound, and the R×10kΩ file can even light up the light-emitting diode (LED).

3. In the voltage range, the internal resistance of the pointer meter is relatively tiny compared to the digital meter, and the measurement accuracy is rather poor. Cannot accurately measure it in some high-voltage and micro-current situations because the internal resistance will affect the circuit under test. For example, when calculating the acceleration stage voltage of a TV picture tube. The measured value will be much lower than the actual value). The internal resistance of the voltage range of the digital meter is considerable, at least in the megohm level, and has little impact on the circuit under test. However, the exceptionally high output impedance makes it susceptible to induced voltage, and the measured data may be false on some occasions with substantial electromagnetic interference.

4. In a word, the pointer meter is suitable for analog circuit measurement with relatively high current and high voltage, such as TV and audio amplifier. Digital meters are ideal for low voltage and small current digital circuit measurement, such as BP machines, mobile phones, etc. It is not absolute and can select pointer tables and digital tables according to the situation.

2. Measurement skills (if not specified, it refers to the pointer table)

1. Measuring speakers, earphones, and dynamic microphones: use R×1Ω gear, connect one end of any test lead, and touch the other end with the other test lead. Under normal circumstances, it will emit a crisp and loud “da” sound. If there is no sound, the coil is broken. If the sound is small and sharp, rubbing the ring and not using it is a problem.

2. Capacitance measurement: Use the resistance gear, select the appropriate range according to the capacitance capacity, and pay attention to the positive electrode of the capacitor for the black test lead of the electrolytic capacitor during measurement.

①. Estimate the size of the microwave-class capacitor capacity: it can be determined by experience or by referring to the standard capacitor of the same power, according to the maximum amplitude of the pointer swing. The reference capacitors do not have to have the same withstand voltage value, as long as the capacity is the same. For example, estimating a 100μF/250V capacitor can be referenced by a 100μF/25V capacitor. As long as the maximum amplitude of their pointer swings is the same, it can conclude that the capacity is the same.

②. Estimate the capacitance of the picofarad-level capacitor: use the R×10kΩ file, but can measure only the capacitance above 1000pF. For 1000pF or slightly larger capacitors, as long as the needle swings somewhat, it can consider that the capacity is sufficient.

3. Measure whether the capacitor is leaking: For capacitors above 1,000 microfarads, you can use the R×10Ω gear to charge it first quickly, and initially estimate the capacitance, then change to the R×1kΩ gear and continue to measure for a while. Should return, but should stop at or very close to ∞. Otherwise, there will be leakage. For some timing or oscillating capacitors below tens of microfarads (such as the oscillating capacitors of color TV switching power supplies), their leakage characteristics are very demanding; as long as there is a slight leakage, they cannot use them. Then use the R×10kΩ gear to continue the measurement, and the needle should stop ∞ instead of returning.

3. Test the quality of diodes, triodes, and Zener tubes on the road: because in actual circuits, the bias resistors of transistors or diodes and the peripheral resistance of Zener tubes are generally relatively large, mostly above hundreds of thousands of ohms, so, we can use the R×10Ω or R×1Ω gear of the multimeter to measure the quality of the PN junction on the road. When measuring on the street, use the R×10Ω equipment to measure the PN junction should have apparent forward and reverse characteristics (if the difference between the forward and reverse resistance is not clear, you can use the R×1Ω gear to measure). Generally, the forward resistance is at R. The needle should indicate about 200Ω when measuring in the ×10Ω equipment, and around 30Ω when measuring in the R×1Ω gear (there may be slight differences depending on the phenotype). If the forward resistance value of the measurement result is too large or the reverse resistance value is too small, there is a problem with the PN junction, and there is a problem with the tube. This method is particularly effective for repairs, where can found foul lines quickly, and even pipes that are not entirely broken but have deteriorated characteristics can be detected. For example, when you measure the forward resistance of a PN junction with a slight resistance value, if you solder it down and test it again with the commonly used R×1kΩ file, it may be expected. The characteristics of this tube have deteriorated. Not working correctly or unstable anymore.

4. Resistance measurement: It is essential to choose a reasonable range. When the pointer indicates 1/3 to 2/3 of the total capacity, the measurement accuracy is the highest, and the reading is the most accurate. It should be noted that when using the R×10k resistance gear to measure the considerable resistance value of the megohm level, do not pinch your fingers at both ends of the resistance so that the resistance of the human body will make the measurement result small.

5. Measure the Zener diode: the voltage regulator value of the Zener diode we usually use is generally greater than 1.5V. The 1.5V battery in the meter powers the resistance file below R×1k of the pointer meter. The resistance range below R×1k is the same as measuring the diode, complete unidirectional conductivity. However, the R×10k gear of the pointer meter is powered by a 9V or 15V battery. The reverse resistance value will not be specific when using R×10k to measure a voltage regulator tube with a voltage regulation value less than 9V or 15V. Resistance, but this resistance is still much higher than the forward resistance of the Zener tube. In this way, we can preliminarily estimate the quality of the Zener tube. However, a suitable voltage regulator must have an accurate voltage regulation value. How to estimate this voltage regulation value under amateur conditions? It’s not complicated; find another pointer watch. The method is first to place a look in the R×10k gear, and the black and red test pens are connected to the cathode and anode of the voltage regulator tube, respectively. At this time, the actual working state of the voltage regulator tube is simulated. Then another watch is placed on the voltage range V×10V or V×50V (according to the voltage regulation value), connecting the red and black test leads to the watch’s black and red test leads just now. The voltage value measured at this time is the Zener tube’s voltage regulator value. Saying “basically” is because the bias current of the first watch to the voltage regulator tube is slightly smaller than the bias current in everyday use so that the measured voltage regulation value will be slightly larger, but the difference is the same. This method can only estimate the voltage regulator tube whose voltage regulation value is less than the voltage of the pointer meter’s high voltage battery. Suppose the voltage regulation value of the Zener tube is too high. In that case, it can only be measured using an external power supply (in this way, when we choose a pointer meter, it is more suitable to select a high-voltage battery with a voltage of 15V than 9V).

6. Measure the triode: usually, we use the R×1kΩ file, whether an NPN tube or a PNP tube, whether it is a low-power, medium-power, or high-power line, should measure the be junction CB junction. Electricity’s reverse resistance is infinite, and its forward resistance is about 10K. If necessary, change the resistance gear for multiple measurements to further estimate the quality of tube characteristics. The method is: set the R×10Ω equipment to measure the forward conduction resistance of the PN junction at about 200Ω; set the R×1Ω gear to measure The bold conduction resistance of the PN junction is about 30Ω. (The above is the measured data of the 47-type meter, and other models are slightly different. You can test a few more good tubes to summarize so that you can know what you have in mind.) If the reading is too large, too many, it can conclude that the characteristics of the tube are not good. You can also place the meter in R×10kΩ and test again. The line with low withstand voltage (basically the withstand voltage of the triode is above 30V), the reverse resistance of its CB junction should also be ∞. Still, the reverse resistance of its be junction There may be some, and the needle will deflect slightly (generally not more than 1/3 of the full scale, depending on the pressure resistance of the tube). Similarly, when measuring the resistance between ec (for NPN tube) or ce (for PNP tube) with R×10kΩ, the needle may deflect slightly, but this does not mean that the tube is nasty. However, when measuring the resistance between ce or ec with the gear below R×1kΩ, the meter’s indication should be infinite. Otherwise, there is a problem with the tube. It should note that the above measurements are for silicon tubes and do not apply to germanium tubes. But now, germanium tubes are also rare. In addition, the so-called “reverse” refers to the PN junction, and the direction of the NPN tube and the PNP tube is different.

Use case – use a multimeter to accurately determine the b, c, and e polarities of the pins of the triode

Most of the typical triodes are plastic-encapsulated now. How to accurately judge which of the three pins of the triode is b, c, and e? The b pole of the triode is easy to measure, but how to determine which is c and which is e?

The first method: For the pointer meter with the hFE jack of the measuring transistor, first measure the b pole, insert the transistor into the jack at will (of course, can insert the b pole accurately), measure the hFE value, and then turn the tube upside down and measure it again. The measured hFE value is relatively large once, and the insertion position of each pin is correct.

The second method: For the meter without hFE measurement jack, or the tube is too large to be inserted into the jack; this method can be used: for the NPN tube, first measure the b pole (whether the tube is NPN or PNP and its b pin). It is easy to measure, right?). Still, the meter in the R×1kΩ gear connects the red test lead to the hypothetical e pole (be careful not to touch the tip or pin of the test pen with the hand holding the red test lead) and connect the black test lead to the hypothetical e-pole C pole. Pinch the tip of the test lead and this pin with your fingers simultaneously, pick up the tube, lick the b pole with your tongue, and see that the meter’s pointer should have a certain deflection. If you connect the test pens correctly, the pointer deflection will If it is more prominent if it is not linked correctly, the deflection of the pointer will be minor, and the difference is noticeable. From this, we can determine the c and e poles of the tube. For the PNP tube, connect the black test lead to the hypothetical e-pole (do not touch the pen tip or pin), and the red test leads to the hypothetical c-pole, at the same time pinch the test lead and this pin with your fingers, and then lick b with the tip of your tongue. Significantly, if the test leads are connected correctly, the pointer of the meter head will be deflected relatively large. Of course, when measuring, the test leads need to be exchanged twice and can be made the final judgment after comparing the readings. This method is suitable for all shapes of triodes, which is convenient and practical. According to the deflection of the needle, the magnification capacity of the tube can also be estimated. Of course, this is based on experience.

The third method: first determine the NPN or PNP type of the tube and its b pole, then put the meter in the R×10kΩ gear. When the black test lead is connected to the bar for the NPN tube, and the red test lead is connected to the c pole, the needle may have a certain amount. Deflection, for the PNP tube, when the black test lead is connected to the c pole and the red test lead is connected to the bar, the needle may be deflected to a certain extent, and vice versa. From this, also determine the c and e poles of the triode can. However, this method is not suitable for high-pressure pipes. The c pole is basically in the middle (I haven’t seen b in the middle). The b of the medium and small power tubes is very likely to be in the middle. For example, the commonly used 9014 triode and other triodes in its series are 2SC1815, 2N5401, 2N5551, and other triodes, some of which are in the middle. Of course, they also have the C pole in the middle. Therefore, repairing and replacing triodes, especially these low-power triodes, cannot be installed as they are, and they must test first.

Multimeter usage formula

Correct use of the multimeter can quickly and accurately determine the fault location and prevent damage to electrical equipment and the multimeter itself.

1. When measuring, look at the block first, and do not measure without looking.

Every time you pick up the test leads and prepare to measure, be sure to check again whether the measurement category and range selection switches are in the correct positions. For safety, one must develop this habit.

2. Do not shift the gear when measuring, and then turn the neutral gear after the measurement

During the measurement, the selection knob cannot be turned arbitrarily, especially when measuring high voltage (such as 220V) or high current (such as 0.5A) to avoid arcing and burning out the contacts of the transfer switch. After the measurement is completed, the range selection switch should be moved to the “•” position.

3. The dial should be level, and the reading should be aligned

When using the multimeter, it should rotate it horizontally, and the line of sight should be facing the needle when reading.

4. The range should be appropriate, and the needle is more than half off.

When selecting the range, if you cannot estimate the measurand’s size in advance, you should try to choose a more extensive coverage and then gradually change to a smaller range according to the deflection angle until the pointer is deflected about 2/3 of the full scale.

5. Test R is not charged; test C discharge first

It is strictly forbidden to measure resistance when the circuit under test has a point. When checking large-capacity capacitors on electrical equipment, the capacitors should be short-circuited and discharged before measurement.

6. Measure R to zero first, and zero to shift gears

When measuring resistance, first turn the switch to the electric block, short-circuit the two test leads, and turn the “Ω” zero-adjustment potentiometer to make the pointer point zero ohms before measuring. The ohmic zero should be readjusted every time the electrical barrier is replaced.

7. Should remember the black and negative clearly and connect the black in the table to “+.”

The red test lead is the positive electrode, and the black test lead is the negative electrode, but the black test lead is connected to the positive electrode of the internal battery.

8. The measurement I should be connected in series and should connect the measurement U in parallel

When measuring current, the multimeter should be connected in series in the circuit under test; when measuring voltage, the multimeter should be connected in parallel at both ends under test.

9. The polarity is not reversed, and one hand becomes a habit

When measuring current and voltage, one should pay special attention to the contradictions of the red and black test leads that cannot be reversed and must develop the habit of one-handed operation to ensure safety.

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