Special functions and areas of application for the multimeters
Multimeter with more features, easy to use has become an essential tool in the hands of electrical and electronic engineers, but if you want to give full play to its role, fast and accurate to get accurate data. Then we also need to know more about some of the qualities of the multimeter:
1. digital multimeter must be better than analogue multimeter?
Solution: Digital multimeter with its accuracy and sensitivity, fast measurement speed, multi-functional, small size, high input impedance, easy to observe and strong communication features and other excellent qualities, quickly be applied. There is a trend to replace the analogue pointer meter.
But in some occasions, such as electromagnetic interference is very strong occasions with a digital multimeter test data may deviate greatly, because the digital multimeter input impedance is very high, very susceptible to the influence of inductive potential.
2. in the maintenance, through the elimination method suspected that the diode or transistor in the circuit may be damaged. But with a digital meter diode file measured its conduction voltage of about 0.6V, reverse infinity. No problem, and then check the circuit is no fault found, why?
Solution: Most of the digital meter diode file issued by the test voltage of about 3 ~ 4.5V, if the test transistor has a slight leakage or characteristic curve has become bad, in such a low voltage can not be seen. At this time we must use analogue table × 10K resistance file, the file issued by the test voltage of 10V or 15V, in the test voltage will be found to be suspected of transistor leakage in the reverse direction. Similarly in the measurement of some very low voltage resistance of precision sensitive components, the use of analogue meters are very easy to damage the sensitive components. This time to use a digital meter to measure. 3.
3. with a multimeter to measure the high voltage probe attenuation of the voltage value, the results found that the DCV test is more accurate, but the ACV error is very large. Even with a highly accurate multimeter, this is also the case, why?
Solution: The vast majority of multimeters are used in parallel to measure the voltage, the entire test circuit for the voltmeter itself is equivalent to a load is the input impedance. The larger the load impedance, the smaller the effect on the circuit under test, and the more accurate the test. But nothing can be perfect, high impedance should be sacrificed to test the bandwidth. Currently on the market in the frequency response of about 100KHz multimeter input impedance of 1.1M or so, so in the test of high-resistance load voltage at the end of 2 will have a great impact, such as high-voltage probe itself is very high resistance. At this time you have to choose a high internal resistance of the multimeter, such as ESCORT (Fortune) 170/172/176/178/179 handheld digital multimeter to test the ACV provides up to 10,000Ω input impedance, which can avoid the problem.
