Can Analog Multimeters Be Replaced by Digital Multimeters?
Undoubtedly, a multimeter can be said to be the most commonly used electronic measuring instrument for electricians, but choosing a digital multimeter or an analog (pointer) multimeter is a problem. Some people say that digital multimeter has gradually replaced analog multimeter, but many professional electricians are still more accustomed to using analog multimeter. What are the differences between a digital multimeter and an analog multimeter? Which one is better to use?
Firstly, the biggest difference between a digital multimeter and an analog multimeter is that the reading is displayed. The digital multimeter is a liquid crystal display with high resolution, which can fundamentally eliminate parallax when reading data, making the reading relatively convenient and accurate. In this regard, analog multimeter cannot be compared, but it also has its own unique advantage, which is that it can intuitively reflect the changes in the properties of the measured object through the instantaneous deflection of the pointer.
Due to the intermittent measurement and display of digital multimeter, it is not convenient to observe the continuous change process and trend of the measured electricity quantity. For example, a digital multimeter may not be as convenient and intuitive as an analog multimeter in verifying the charging process of capacitors, the variation of thermistor resistance values with temperature, and observing the variation characteristics of thermistor resistance values with light.
In terms of working principle, analog multimeter and digital multimeter are also different. The internal structure of analog multimeter includes a meter head, resistor, and battery, among which the meter head is generally a magnetoelectric DC microampere meter. When measuring resistance, only the internal battery needs to be used. The positive pole of the battery is connected to a black lead, so the current flows out of the black lead and into the red lead. When measuring DC current, shunt resistance is used to expand the range by shifting gears and connecting parallel resistors, as the full bias current of the meter head is very small. When measuring DC voltage, series resistors are connected to the meter head to achieve conversion between different ranges through different additional resistors.
A digital multimeter is composed of a function converter, A/D converter, LCD display (liquid crystal display), power supply, and function/range conversion switch. The A/D converter generally uses ICL7106 dual integral A/D converter. ICL7106 adopts two integrations, the first integrating V1 of the input analog signal, which is called the sampling process; The second integration of the reference voltage - VEF is called the comparison process. Count the two integration processes through a binary counter, convert them into digital quantities, and display them in digital form. To measure AC voltage, current, resistance, capacitance, diode forward voltage drop, transistor amplification factor, and other electrical quantities, corresponding converters must be added to convert the measured electrical quantity into a DC voltage signal.
There is a difference in the polarity of the battery connected internally between a digital multimeter and a pointer type multimeter: the digital red lead is connected to the positive pole of the battery, while the black lead is connected to the negative pole, while the pointer type happens to be the opposite. The diode measured by the digital meter exactly matches the actual polarity of the diode, while the pointer type is exactly the opposite.
In use, analog multimeters are equipped with mechanical zero adjustment knobs or adjustment screws. If it is found that the needle is not pointing to the mechanical zero position (i.e. the zero point of the voltage scale or the infinity of the ohm scale), it is necessary to gently and slowly rotate the mechanical zero adjustment mechanism with a finger or screwdriver to return the needle to zero to eliminate zero error. And the digital multimeter has an automatic zero return function, which is more convenient.
In addition, many digital multimeters now have added many functional ranges compared to pointer multimeters, such as capacitance, frequency, temperature, transistor measurement range, etc., which have also improved sensitivity, accuracy, and overload capacity. Overall, digital multimeter has obvious advantages, but it cannot completely replace analog multimeter. In different measurement scenarios, each has its own advantages and needs to be selected according to their actual measurement needs.
