Measurement of MOS field effect tube of digital multimeter
1. Voltage file:
When testing or manufacturing, it can be used to measure the voltage of each pin of the device, and compare it with the normal voltage to find out whether it is damaged. It can also be used to detect the voltage regulation value of the Zener diode with a small voltage regulation value. The principle is shown in the figure: R is 1K, and the voltage at the power supply terminal depends on the nominal voltage regulation value of the Zener diode, which is generally larger than the nominal voltage. More than 3V, but not more than 15V. Then use a multimeter to detect the voltage value at both ends of tube D, which is the actual regulated voltage value of tube D.
2. Current gear
Connect the meter in series to the circuit to measure and monitor the current. If the current deviates far from the normal value (based on experience or the original normal parameters), the circuit can be adjusted or repaired if necessary. You can also use the 20A range of the meter to measure the short-circuit current of the battery, that is, connect the two test leads directly to the two ends of the battery. Remember that the time must not exceed 1 second! Note: This method is only suitable for dry batteries, AAA and AAA rechargeable batteries, and beginners must be under the guidance of personnel familiar with maintenance, and must not operate by themselves! The performance of the battery can be judged according to the short-circuit current. In the case of a fully charged battery of the same type, the larger the short-circuit current, the better.
3. Resistance file;
One of the methods that can be used to judge the quality of resistors, diodes, and triodes. When the actual resistance value of the resistor deviates too much from the nominal value, it is damaged. For the two-transistor, if the resistance between any two pins is not very large (above hundreds of K), it can be considered that the performance has declined or has been damaged by breakdown. Note that this triode is not blocked. This method can also be used for integrated blocks. It should be noted that: the measurement of integrated blocks can only be compared with the normal parameters.
4. The test leads of ordinary multimeters have a large resistance value. Interested enthusiasts can make a pair of test leads by themselves; method: prepare high-quality speaker wires or multi-core copper wires of about one meter, and a pair of clips with insulating sleeves (red Black), a pair of banana plugs (red and black) for speaker wiring; one end of the line is welded firmly on the clip, and the other end is connected to the banana plug; a pair of good test leads is done.
