Basic Questions and Answers on the Use of Multimeter

　　Multimeters have become an indispensable tool for electronic and electrical engineers because of their many functions and ease of use. However, if we want to fully demonstrate their effectiveness and obtain accurate data quickly and accurately, we need to have a deeper understanding of some characteristics of multimeters:
　　1. Is a digital multimeter definitely better than an analog multimeter?
　　Answer: Digital multimeters are widely used due to their high accuracy and sensitivity, fast measurement speed, multiple functions, small size, high input impedance, easy to check and powerful communication functions. There is a trend of replacing analog pointer meters.
　　However, in some occasions, such as places with very strong electromagnetic interference, the data checked by a digital multimeter may be very wrong, because the input impedance of a digital multimeter is very high and it is easily affected by the induced potential.

　　2. During the repair, the diode or transistor in the circuit may be damaged through the troubleshooting method. However, the on-state voltage measured by the diode range of the digital meter is about 0.6V, and the reverse direction is infinite. There is no doubt that no fault is found when checking the circuit again. Why?
　　Solution: The test voltage announced by the diode range of most digital meters is about 3~4.5V. If the transistor under test has a slight leakage or the characteristic curve has been deteriorated, it cannot be displayed at such a low voltage. At this time, the analog meter × 10K resistance range must be used. The test voltage announced by this range is 10V or 15V. At this test voltage, it will be found that the suspected transistor has leakage in the reverse direction. Similarly, when measuring the resistance of some delicate sensitive components with very low withstand voltage, it is easy to damage the sensitive components using the analog meter. At this time, a digital meter must be used for measurement.

　　3. Use a multimeter to measure the voltage value after the high-voltage probe is attenuated. It is found that the DCV test is more accurate, but the ACV error is large. This is true even if a high-precision multimeter is used. What is the reason?
　　Answer: Most multimeters use the parallel method to measure voltage. For the entire test circuit, the voltmeter itself is equivalent to a load, that is, the input impedance. The larger the load impedance, the smaller the impact on the measured circuit, and the more accurate the test. However, nothing can be perfect. High impedance will sacrifice the test bandwidth. The input impedance of the multimeter with a frequency response of about 10KHz on the market is about 1.1M, so it will have a great impact when testing the voltage at the two ends of the high-resistance load. For example, the resistance of the high-voltage probe itself is very high. At this time, you need to use a multimeter with high internal resistance. For example, the ESCORT (owned) 170/172/176/178/179 handheld digital multimeter provides an input impedance of up to 10,000Ω when testing ACV, which can avoid this problem.

　　4. In my practical test, I want to measure voltage, current, motor winding impedance, and speed. Is there any multimeter that can achieve this function?
　　Answer: ESCORT (owned) -172 handheld digital multimeter can meet your above requirements. At the same time, its safety regulations meet the International Electrotechnical Commission IEC + + 1 CATII + 00V, CATIII 600V standards, so you can use it with confidence even in three types of environments without worrying about safety issues.

　　5. Is there a digital multimeter that is very cheap, has good functions, is reliable and stable?
　　Answer: If there is such a good thing in the world, please tell me :). But relatively speaking, the digital multimeter produced by Taiwan ESCORT (Fuyu) has a higher cost performance.

　　6. What is traceability?
　　Answer: Traceability is the property that a measurement result or measurement standard value can be linked to a regular reference standard, usually a national measurement standard or an international measurement standard, through a continuous comparison chain with a degree of regular uncertainty. That is, professional metrology tools -----> metrology standard tools -----> metrology reference tools. For example, the unit of mass that we come into contact with most in our daily lives: kilogram, its standard is based on the mass of a 1 kg platinum-iridium alloy cylindrical weight stored in a three-layer locked safe in a castle in Sèvres, Paris. All mass units in the world are based on this. Similarly, DCV 1V/ten V is based on the Josephson quantum voltage array stored in the Paris World Metrology Bureau.