Are mercury thermometers truly more accurate than Class A thermal resistors?
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To reduce errors, we chose Class A thermoresistors. The wiring is not connected to the DCS; instead, a digital display unit is placed next to the equipment inside an explosion-proof box. However, for process control purposes, a mercury thermometer is still required due to its higher accuracy I’ve never used a mercury thermometer, but I know that the thermometers we have at home are made of mercury. So does mercury really have such a significant advantage over thermistors?
Look at the accuracy class of the mercury thermometer; what do you think about a mercury thermometer with a range of -200 to 300?
This post was last edited by chenyan4244 on 2015-7-13 at 10:38. I have never used mercury; I’ve not even seen it, so I don’t have any opinion on the matter. I’m not sure if it’s possible or not. If you know, seniors, please let me know. The operating temperature is around 150. Could you please provide information on the precision grades of mercury, as well as its price and performance? I couldn’t find the answers I was looking for on Baidu or within this website
This post was last edited by bd4kg on 2015-7-13 10:49. What is the scale of your mercury thermometer? First-class mercury thermometers are calibrated against second-class mercury ones, and there are models with precision of 0.1 and 0.05. It’s likely that such thermometers aren’t used on site; they’re rarely employed in modern industrial production. You can just send your resistor for testing directly
There are many mercury thermometers at the site of our boilers; since they’re not connected to the DCS and are only used for local monitoring, they serve merely as a reference, and no one pays attention if they get damaged
The Work Safety Administration said that production was banned in China in 2020, but it didn’t state that it couldn’t be used; it only said that we shouldn’t use it either. But now people can find ways to circumvent these rules
The accuracy of mercury thermometers can be very high; for example, the common fever thermometers are one such example. However, their measurement range is limited. In industrial applications, where a large measurement range is required, increasing accuracy necessitates making the thermometer longer
It is strictly prohibited in industry, and it is no longer used in hospitals either.
Mercury thermometers are direct-reading instruments. In other words, it can obtain readings without any form of signal conversion. Direct-reading instruments have higher reliability due to the absence of intermediate signal conversion, and therefore are used as the final measurement method in many situations. On some devices, it is even required as a legal mandatory measure. Mercury thermometers (and actually, not only mercury thermometers, but also other direct-reading thermometers such as bimetallic thermometers) generally do not have very high accuracy (as defined in technical measurement terms). However, a higher resolution can be achieved by selecting an appropriate range, which in turn reduces the absolute error of the measurement and enables high precision in the measurement process (not high precision of the measuring instrument itself). Taking a mercury thermometer as an example, its range generally does not exceed 10 degrees, but its resolution (the precision of the scale) can reach 0.1 degrees; in other words, its accuracy is not higher than 0.5 grade, which is lower than 0.2%|t|, one of the accuracy standards for A-grade platinum resistors. But in reality, it is very difficult to achieve a resolution of 0.1 degrees for platinum resistors after conversion and transmission. Moreover, the full accuracy specification for Class A platinum resistors is 1.5°C or 0.2%|t|. Thus, this “precision” is not that “precision”. There is a conceptual difference between the precision you mention and the precision referred to in terms of manufacturing processes. Furthermore, it cannot be generally said that one has an advantage over the other. It’s just using different methods to meet different requirements. In my opinion, given that instructions are given on-site as well, using a bimetallic thermometer is more appropriate than constructing a cabinet or using a mercury thermometer.
Most of the on-site temperature indicators in production equipment use bimetallic thermometers; since they are for local indication, high precision is not required.
No, because there were no instruments in the factory back then, so resistors weren’t used in the manufacturing process. They were reluctant to adopt such \"high-tech\" elements as resistors, and they also had very high requirements regarding temperature accuracy – it was said that the accuracy needed to be 0.1 degrees. Anyway, I think it’s impossible; unless there’s someone standing in front of each reactor, it’s impossible to achieve an accuracy of 0.1 degrees using on-site displays for control. Are they trying to take advantage of the fact that I’ve never done this kind of work before?