Explanation of whether a digital multimeter can replace an analog multimeter
There is no doubt that the multimeter can be said to be the most commonly used electronic measuring instrument for electricians. However, whether to choose a digital multimeter or an analog (pointer-type) multimeter is a question. Some people say that the digital multimeter has gradually replaced the analog multimeter, but many professional veteran electricians are still more accustomed to using the analog multimeter. What are the differences between the digital multimeter and the analog multimeter? Which one is better to use?
First of all, the biggest difference between the digital multimeter and the analog multimeter is the reading display. The digital multimeter has a liquid crystal display with high resolution, which can fundamentally eliminate the parallax when reading data, and the reading is relatively convenient and accurate. In this regard, it is unparalleled by the analog multimeter. However, the analog multimeter also has its own unique advantages, that is, it can intuitively reflect the property changes of the measured object through the instantaneous deflection of the pointer.
Since the digital multimeter measures and displays in an intermittent manner, it is not convenient to observe the continuous change process and the change trend of the measured electrical quantity. For example, when the digital multimeter is used to check the charging process of the capacitor, the law of the resistance change of the thermistor with temperature, and observe the change characteristics of the resistance of the photoresistor with light, it is not as convenient and intuitive as the analog multimeter.
In terms of working principle, the analog multimeter is also different from the digital multimeter. The internal structure of the analog multimeter includes a meter head, resistors, and a battery. The meter head generally uses a magnetoelectric DC microammeter. Only when measuring resistance, the internal battery is used. The positive pole of the battery is connected to the black test lead, so the current flows out of the black test lead and into the red test lead. When measuring the DC current, a shunt resistor is connected by shifting gears to shunt the current. Because the full-scale deflection current of the meter head is very small, a shunt resistor is used to expand the range. When measuring the DC voltage, a resistor is connected in series with the meter head, and different ranges are converted through different additional resistors.
The digital multimeter is composed of a function converter, an A/D converter, an LCD display (liquid crystal display), a power supply, and a function/range conversion switch, etc. The A/D converter generally uses the ICL7106 dual-integral type A/D converter. The ICL7106 uses two integrations. The first is to integrate the input analog signal V1, which is called the sampling process; the second is to integrate the reference voltage -VEF, which is called the comparison process. A binary counter is used to count the two integration processes, convert them into digital quantities, and display them in digital form. When measuring AC voltage, current, resistance, capacitance, the forward voltage drop of the diode, the amplification factor of the transistor and other electrical quantities, corresponding converters must be added to convert the measured electrical quantities into DC voltage signals.
