1. What is the buzzer function for?
A: The buzzer function, yes, an additional function, is generally done in the 2kω range. Generally, when the line (or resistance) with a resistance value below 50ω is measured, the built-in buzzer will sound. In practice, this function has a great effect, can improve the work efficiency of measuring the on-off of the line, and is an essential function for maintenance.
2. Why does the digital multimeter not return to zero when it is short-circuited at 200ω?
Answer: In the 200ω range, due to the resistance value of the line, the internal resistance of the meter and the contact point, some mantissas are normal when short-circuiting. This mantissa will become larger and larger in use and cannot be adjusted. plate, close contact points to reduce the value. In use, short circuit first, and write down the value, then subtract it in the measurement.
3. How to determine if the multimeter is good?
Answer: This is a relatively large problem, and it is a better method to try each function range. When testing, it is necessary to find the detection source first, but it is impossible for ordinary users to prepare their own standard detection source, so the general detection can be measured by qualitative and quantitative methods. The basic solution is to find the detection source and use it according to the instructions.
4. How to proofread the multimeter?
A: The multimeter is the same as other measuring instruments. It is calibrated by the manufacturer when it leaves the factory, so if there is no major obvious problem, please do not adjust it at will. The head of the current multimeter is generally a voltmeter, so when you want to calibrate other gears, you must first adjust the DC voltage gear, which is called the basic gear by industry insiders. Every gear and every function (except resistance gear) may be out of alignment. Generally, a multimeter will set one potentiometer (such as DC voltage file) or multiple potentiometers (such as temperature file) in each function, and some have no potentiometer (such as resistance file). If there is a potentiometer, it is easy to handle, input the detection signal, and then adjust it directly; if there is no potentiometer, it will not be out of alignment.
5. How to judge (detect) whether the DC voltage range (dcv) of the multimeter is good?
Answer: When testing, we must first find the testing source. Because we are qualitative and quantitative measurement, there are many testing sources available. The household testing sources include 1.5v alkaline/carbon batteries (No. 1, No. 5/aa, 7th/aaa), 1.2v rechargeable battery, mobile phone charger, adapter, etc. When testing, turn the multimeter to the required DC voltage level, insert the test leads according to the instructions, connect the testing source, and read the reading on the LCD, as long as the measured value is around the nominal voltage. .
ps: to repeat, we are qualitative plus a little quantitative measurement, so we can use these sources, because the voltage of these sources is not very stable, like a 1.5v battery, the new battery may reach more than 1.6v, and the old battery may only have A few tenths of a volt.
6. What are the safety precautions for using the multimeter?
To avoid possible electrical shock and personal injury, follow these rules:
a. Do not use a damaged meter. Before using the instrument, please check the case of the instrument and pay attention to the insulation near the connection socket.
b. Check the test leads for damaged insulation or exposed metal, check the continuity of the test leads, and replace the damaged test leads before using the meter.
c. When the operation is abnormal, please do not use the meter, so the protection may be damaged. When in doubt, send the meter for overhaul.
d. Please do not use the instrument near explosive gas, steam or dust.
e. Please do not input more than the rated voltage marked on the meter between any two terminals or between any terminal and the earth.
f. Before use, verify the meter by measuring a known voltage with the meter.
g. When measuring current, please turn off the power of the line before connecting the meter into the line.
h. When servicing the meter, use only the indicated replacement parts.
i. Please pay special attention when measuring AC voltage 30v average, 42v peak or DC 60v or more, because such voltages will cause electric shock hazard.
j. When using the test leads, keep your fingers behind the test leads.
k. When measuring, please connect the public test lead (black test lead) before connecting the charged test lead (red test lead); when disconnecting, please disconnect the charged test lead first, and then disconnect the public test lead.
l. When opening the battery compartment, please remove all test leads from the meter.
m. Do not use the meter when the battery compartment or the meter housing part is not tightly closed or loosened.
n. When the battery low voltage instruction symbol “ ” appears, please replace the battery as soon as possible to avoid possible electric shock or personal injury caused by misreading.
o. Please do not use a multimeter to measure voltages other than the cat classification level indicated by the multimeter.
7. How to judge (detect) whether the AC voltage (acv) of the multimeter is good?
Answer: Household detection sources include AC adapters, household sockets (two-phase 220v, it is best not to measure three-phase 380v, because this voltage is more dangerous, for the instrument (at least a multimeter with cat iii 600v or more) and Users have higher requirements). For safety reasons, it is recommended to measure relatively small voltages, such as AC adapters, and then measure the voltage of household sockets. For specific safe operation methods, please refer to the product manual.
8. How to judge the quality of the resistance gear (ohm ω)?
Answer: Note, please do not use the resistance gear to measure the voltage. When measuring online, the equipment should be powered off, and there should be a battery or battery line, and it should be fully discharged before measurement. This is relatively easy to detect. Generally, those who are engaged in electronic maintenance and have some resistance components on hand can directly measure the resistance value.
9. How to judge the quality of DC current gear (dca)?
Answer: If there is a known current source, input it directly in the current range. If not, it doesn't matter. Just input the voltage in the current range. value, please also note the following:
a. Please do not input too high voltage, so as to avoid too much current and damage the meter. Commonly used sources that can be input are ordinary batteries, such as No. 5, No. 7, etc.;
b. When measuring the current of the input voltage, because the resistance (load) of the internal resistance of the meter is very small, if the input is too long, the source will be damaged, so try not to exceed 5 seconds for a single input;
c. Each high and low range, adjacent range, is generally 10 times the relationship.
10. How to judge the quality of the capacitor file (cap)?
Answer: Generally, find a capacitor with a known value and insert it directly for measurement. The displayed value of each range should be in a 10-fold ratio; it is best to use a good metal capacitor for testing, which has stable capacity and high precision. It is not recommended to use electrolytic capacitors for testing, because electrolytic capacitors have poor stability and accuracy.
11. What is the basic working principle of a digital multimeter?
Answer: The basic circuit of a digital multimeter is a meter circuit, and its basic function is to quantify the input DC voltage (analog quantity) and output it; other functions generally require the addition of external circuits. ps: Now the multimeter's chip, its integration is getting higher and higher, and the peripheral circuits are getting less and less, which has advantages and disadvantages. Advantages: high integration, simple external circuits, and fewer quality failures caused by component quality problems; disadvantages: once the chip is broken, the replacement cost is high and troublesome. Sometimes the money for replacing one chip can buy another meter, so Generally broken and had to be scrapped.
12. What is the difference between three and a half digits and four and a half digits of a digital multimeter?
Answer: Three and a half are also called 3 1/2 digits (pronounced three and one-half digits), and four and a half digits are also called 4 1/2 (pronounced four and a half digits). We know that after an analog quantity is quantized and converted into a number, the precision represented by it is related to the number of digits of the number. The more digits, the closer to the original value, the more accurate (this is generally speaking , regardless of other circumstances, if the quantized value is 1.00000v, the one-bit representation is the same as the n-bit representation (:). So in general, the more digits, the more accurate, that is, four digits Half is more accurate than three and a half.
13. How is the accuracy (uncertainty) of a digital multimeter calculated?
Answer: The accuracy of the multimeter is also called uncertainty by some manufacturers, which generally reads "within one year from the factory, the operating temperature is 18°c ~ 28°c (64°f ~ 82°f), and the relative humidity is less than 80%. , ±(0.8% reading + 2 digits)." Many buyers or users are not very clear about this and often ask. I assume here that there is a meter, in a certain range, such as DC 200v gear, it is written like this, the measured value displays 100.0 on the meter, then the correct value at this time should be. I think that for the average user, you can completely ignore the precision calculation and directly think that it is DC 100v. According to the manufacturer's precision calculation, when measuring 100v (display 100.0), the error is ±(0.8%*1000+2)=±10, that is, the error is 1.0v. When substituting the reading, do not consider its decimal point to display Substitute the value into the calculation, add the decimal point to the calculated value, and then use the original reading to send the freight, like this example, then the correct value is 100.0±1.0, which should be between 99.0 and 101.0v DC.
14. I am a rookie and want to learn electronic maintenance. What kind of multimeter should I buy?
Answer: Under normal circumstances, a friend who is just getting started can buy a universal multimeter (three-meter, named because it can measure voltage, current, and resistance at the same time). The most used function is resistance, and then DC voltage. , The additional functions of the multimeter, the buzzer function, and the capacitance measurement are also used more, and you should consider purchasing a meter with this function. Of course, there are some skilled maintenance personnel who may have their own unique maintenance methods, which is another matter. The most cost-effective multimeters that meet these functions are dt9205a or m890d, which are standard models. Some manufacturers call them dt9205, dt9205n, dt9205l, dt9205b, and dt9205m. In fact, the functions are similar. As long as you look for the function, you don't need to pay attention to the difference of the model.
15. How to use a multimeter to detect damaged electronic products or household appliances?
A: This question is very complicated, or it turns me on the wrong side. For electronic product maintenance, or brain maintenance, everyone has their own methods, and it is impossible to generalize. In general, a multimeter is just a tool with many functions (that is, it can measure many parameters). By proficiently measuring each segment of the circuit or each parameter and its synthesis, the fault can be judged. For example, by measuring the voltage of a certain circuit to determine whether it is working properly; by measuring the resistance of a component to determine whether it is normal; by measuring the capacitance of a component to determine whether it is open, short-circuited or deteriorated . . . . and many more. So the multimeter is just a tool. After you buy it back, you should also bubble in various forums, or participate in amateur classes, in order to strengthen your literacy and improve the ability to use the tool. Finally, for example, a multimeter is like a sword. Its power lies in its owner. With a few percent of martial arts (electronic knowledge), it can play a few percent of the effect.
