Analysis and Comparison of Intelligent Digital Display Meters and Analog Display Meters

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With the rapid development of science and technology, control systems such as DCS and PLC have replaced conventional instruments in the industrial sector and are widely used. In particular, large and medium-sized factories (plants) almost always employ such control systems. However, for some auxiliary processes and devices, it is still necessary to use conventional panel-mounted instruments. This is especially true for smaller factories or plants where the number of measurement and control points is limited; using control systems like DCS or PLC would not be cost-effective in such cases. During our visits abroad, we also found that DCS and PLC control systems are not used in every situation – it is necessary to decide, based on specific circumstances, whether to use such control systems or conventional panel-mounted instruments. Conventional panel-mounted instruments come in two different types: intelligent digital display instruments and analog display instruments. This article was first published on the WeChat official account “Automation Classroom”. So what are the differences in performance between these two types of instruments? We conduct analysis and comparison from the following 5 aspects: 1. Input signal aspect: Analog display instruments usually can only accept standard signals (such as 4~20mA) or select one type of input signal such as platinum resistance thermometers or thermocouples; the scale range of the instrument cannot be changed flexibly ； Intelligent digital display instruments can accept a variety of input signals; with simple configuration, they can handle DC millivolts, volts, milliamperes, thermocouples, thermal resistors, standard signals, etc., and it is convenient to set the measurement range and scale range. 2. In terms of measurement accuracy: Smart digital display meters provide easy-to-read readings without parallax error ； The display accuracy of intelligent digital meters can reach ±0.05% of the full scale plus 2 digits, with a recording accuracy of ±0.1% of the full scale; in contrast, analog meters generally have an accuracy of only ±0.5% of the full scale. 3. In terms of recording functionality: Intelligent digital display meters offer trend recording similar to that of analog recorders, as well as tabular recording. They also feature functions such as zero-point shift of the recorded curves (i.e., automatic range switching), segmented recording, and zooming in/out of the records. The measurement and recording speeds are very high, and the recorded curves for different channels can be synchronized in terms of time. On the other hand, the function of the analog recorder is limited to recording trend curves, and its recording speed is slow. 4. In terms of calculation functions: Since smart digital display instruments are equipped with microprocessors, they have the capability to perform calculations. In addition to the four basic arithmetic operations, they can also carry out functions such as square root calculation, absolute value calculation, average value calculation, and logical operations; moreover, they can automatically display and record any abnormal conditions. All of these are beyond the reach of analog display instruments. 5. In terms of interfaces: Intelligent digital display meters can communicate with computers through interfaces, thereby integrating the recorders into computer management systems. And simulation display instruments can only be used independently. So here’s the question: although smart display instruments have so many advantages and seem capable of completely replacing analog instruments, why do we still use analog instruments in some practical applications? Do you know why?