【 Weak current College 】 digital multimeter special use skill 】

First, the structure of the digital multimeter

Digital multimeter is a digital voltmeter with corresponding features conversion circuit, it can be on AC, DC voltage AC, DC current, resistance, capacitance, frequency and other parameters for direct measurement. Digital voltmeter typically use a piece of IC chip, it will be A/D converter and can direct drive monitors display logic controller integrated in the surrounding with related resistor, capacitor and monitor,, the digital multimeter header. It only measuring DC voltage, and other parameters must be converted to and its own size proportional relationship of the DC voltage can be measured. Digital multimeter's overall performance, mainly by the performance of a digital meter. Digital Voltmeter is the core of digital multimeter, A/D converter is the core of digital voltmeter, different poses A/D converter for DMM different principle. Functional conversion circuit is digital multimeter measurement of multiple parameters essential circuits. Voltage and current measurement circuit by passive partial pressure, shunt resistor network; AC, DC conversion circuit with resistors, capacitors and other electrical parameter measuring conversion circuit, generally use active devices to a network. Feature selection is available through the mechanical switch switch, range selection switch via switch or by automatic range switching circuit.

Second, using diode stalls and 200 M Ω stalls discriminant triode

1. switch on the back of the multimeter, diode stalls digital multimeter diode stalls around the voltage output 2.7V, use one-way conductivity pn junction, judgment and judgment b very NPN, PNP-transistor.

(1) assuming that the transistor is a b, red table amount received in the assumption of b, the black table pens respectively two other extremely testing their resistance, if two measured resistance are low resistance and roughly equivalent, then on the change table pen testing their resistance is high and they are equal, then red is looking for b, and judgement is a NPN-type tubes.

(2) if the red table amount received extremely hypothetical b, according to the results of the measurement, are high resistance and are equal, the swap table pen testing their resistance is low resistance and are equal, the black table amount received as a, and b to PNP.

(3) if the above method results in a measured as low resistance, a high resistance, the original hypothesis of b is wrong and must be assumed that the other foot to b until you meet the requirements. When the three measured results is not equal to the resistance, the transistor is bad.

2. switch on the back of the multimeter resistance 200 M Ω stalls for NPN-type tube, assume its a very great c, red table amount received in the assumption of c very, black table amount received e-pole, or hand squeeze b and c, but not touch. This is in order for bc interconnect bias resistor to the transistor's base electrode with a forward current, transistor breakover. Note at this point of resistance, then red and black table pen swap re-test, and write down their resistance, compared to twice the size of the resistance, the resistance is small, which shows which assumption is correct, that the red table amount received is very c. On the contrary, the PNP-tube, the black table amount received is very c.

Note: digital multimeter and mechanical multimeter red and black table pens instead.