multimeter

Security system maintenance and home appliance maintenance, car maintenance and other maintenance methods are basically the same, often with the help of a variety of instruments, instruments and tools. So as a security system maintenance technician, we must first learn and our industry related instruments, meters, tools and so on. Only by mastering and using these instruments and tools can we get twice the result with half the effort in maintenance. So in this chapter, we learn about the instruments, meters and tools often used in the security industry. Of course, if you are familiar with the content of this chapter, you can skip this chapter.

1.1 Common instruments and meters

1. Digital multimeter

Security system maintenance, because a lot of equipment is electric, so the digital multimeter is our maintenance of the most commonly used instrument. Of course, the early use of pointer multimeter can also be used, but now the popularity of digital multimeter and easy to use, so we introduce the digital multimeter, hereinafter referred to as the multimeter.

Multimeters are generally used to measure voltage, resistance and so on in maintenance. If there is integrated board failure, but also measure diode, audion and so on all kinds of circuit components. "ω" stands for resistance, "V-" stands for DC voltage, "V ~" stands for AC voltage, "A ~" stands for AC current, "A-" stands for DC current, and "F" stands for capacitance. "HfE" stands for triode, stands for buzzer and diode. All brand multimeters have similar basic functions and the same use methods. As long as we understand the meaning of these symbols on the multimeter, we can basically use it normally. The following describes how to use a multimeter.

multimeter

1.1. Voltage measurement

There are two kinds of voltage used in security system, one is dc voltage, the other is AC voltage. For example, the power supply for the detector is usually DC12 volts (DC12V); The voltage that supplies power to the monitor is usually AC voltage (AC220V). The DC voltage is expressed by DC and the AC voltage by AC.

1. Measurement of DC voltage. First, insert the black stylus into the "COM" hole and the red stylus into the "V ω". Set the knob to a dc voltage range larger than estimated, and then connect the pen to both ends of the power supply to ensure good contact. The value can be read directly from the display screen. If it reads as "1", it indicates that the range is too small, so you need to increase the range before measuring the voltage. If "-" appears on the left of the value, it indicates that the polarity of the pen is opposite to the actual power supply, and the red pen is connected to the negative power supply.

2. Measurement of AC voltage. The pen jack and DC voltage measurement, the knob to the AC file "V ~" the required range can be. Ac voltage is not positive or negative, and the measurement method is the same as that of DC voltage. Whether ac or DC voltage test, should pay attention to personal safety, do not literally touch the metal part of the pen.

1.2. Measurement of current

1. Measurement of DC current. First insert the black marker into the COM hole. If the measurement is greater than 200mA current, the red pen is inserted into the "20A" jack, and the knob is selected to dc "20A" file; If the current measurement is less than 200mA, the red pen into the "200mA" jack, the knob to dc 200mA within the appropriate range. Once adjusted, it is ready to be measured. String the multimeter into the circuit and keep it stable for reading. If the display is "1", then increase the range; If "-" appears on the left of the value, it indicates that the current flows from the black stylus into the multimeter.

2. Measurement of AC current. The measurement method is the same as the DC current measurement. Set the gear to the AC current. After the current measurement is finished, make a good habit of inserting the red pen back into the "V ω" hole. Because if you measure the voltage directly with the current mode, the multimeter will burn out.

1.3 measurement of resistance

Insert the stylus into the "COM" and "V ω" hole, select the knob to "ω" in the required range, with the stylus connected to the metal parts at both ends of the resistance, the resistance can be measured by hand, but do not touch both ends of the resistance at the same time, it will affect the measurement accuracy. Keep good contact between pen and resistor when reading. Note the unit: In the "200" file, the unit is "ω"; in the "2K" to "200K" file, the unit is "K ω"; in the "2M" file, the unit is "M ω".

1.4. Measurement of diodes

Digital multimeter can measure led, rectifier diode, etc., pen position and voltage measurement, the knob to the file; The red pen is connected to the positive pole of the diode, and the black pen is connected to the negative pole, which shows the forward voltage drop of the diode. Schottky diode pressure drop is about 0.2V, ordinary silicon rectifier (1N4000, 1N5400 and other series) about 0.7V, led about 1.8 ~ 2.3V. Replace the pen, the display display "1" is normal, because the reverse resistance of the diode is very large, otherwise the tube has been broken down.

1.5. Measurement of buzzer gear

The digital multimeter has a special gear, which is the buzzer gear shared with the diode. Special because the previous pointer multimeter does not have this gear, and it is shared with the diode, its function and resistance close, equivalent to the resistance of 0 ohms. The biggest advantage of buzzer is intuitive, the main role is to judge whether the circuit is short circuit and open circuit, judge whether components breakdown. The tap position is rotated to, the pen position is the same as the voltage measurement, and the two pens are respectively in contact with both ends of the line. If the buzzer sounds "di", the multimeter displays "0", indicating a short circuit; If the multimeter displays 1 and does not sound, it indicates that the line is open. Similarly measuring components, if the two stylus exchange contact components at both ends, the uniform sound of "di", the multimeter shows "0", indicating the breakdown of components, this method generally refers to the test diode and audion. Buzzer measurement is most commonly used in security system maintenance.

1.6 measurement of triode

Triode measurement, divided into two steps, first determine the triode tube type, and then determine the triode pin. The specific method is as follows: the stylus insert is the same as the measuring voltage; The principle is the same as diode. First assume A foot as the base, with the black pen and the foot contact, red pen and other two feet respectively contact the other two feet; If both readings are about 0.7V, then connect the red pen to pin A and the black pen to the other two pins. If "1" is displayed, then pin A is the base. Otherwise, it needs to be measured again and this tube is A PNP tube. What about the collector and emitter? Digital table can not be used as a pointer table pointer swing to judge, so how to do? We can use the "hfE" file to judge. First select the gear to "hfE" gear, you can see a row of small jacks next to the gear, PNP and NPN tube measurement. The tube type has been determined before, insert the base into the corresponding tube type "B" hole, and insert the other two legs into the "C" and "E" holes respectively. At this time, the value can be read, that is, the β value; Then fixed base, the other two feet switch; Compare the two values, and the pin position with the larger reading corresponds to the multimeter surface "C" and "E".

Note: the above method can only directly measure small triodes, such as 9000 series triodes. If you want to measure large tubes, you can use wiring method, that is, lead the three pins out with small wires and then measure.

Recommended Articles

Leave a Reply