Instrument measurement accuracy

There’s hardly any need for special consideration; the accuracy of transmitters from different manufacturers is more or less similar. It’s just that transmitters of different types have varying levels of accuracy – for example, those of the diaphragm remote transmission type tend to have lower accuracy. The data sheets provided by design institutes also indicate the precision levels that manufacturers can achieve; it’s not possible for manufacturers to produce products with a higher level of precision just because someone requests it. Generally speaking, the precision offered by transmitter manufacturers is more than sufficient to meet industrial requirements. If it is truly necessary, some manufacturers also offer high-precision options, at a slightly higher price. Of course, the accuracy of double-flange transmitters, as you mentioned, is generally around 0.2%. I use EJA models here, and in terms of accuracy they are quite good; they are digital resonant sensors, which means their design is relatively advanced

±The double-flange version with 0.075% FS has not yet been developed; it’s probably just something that that small factory is claiming as a lie

What you said is indeed the case; perhaps I didn’t express myself clearly. What I mean is: if manufacturers offer instruments with a precision of 0.2% or 0.5%, how should we decide which precision to choose? Is it entirely based on experience?

For instruments with this level of precision, the Rosemount-3051 series can be considered.

Double flange – not a differential pressure transmitter

From the perspective of the indicators shown on the instruments: the higher the precision, the more accurate the measurements can be in theory, but the higher the manufacturing standards required. So from a certain perspective, the higher the precision of an instrument, the better it is. In terms of usage: ● The measurement error only needs to be sufficient to meet the requirements. Generally, the relative error in process measurement in chemical production is around 5% (error/% of the measured value), while the default relative error for international trade is 3% ； ●The relative error can be converted in relation to the instrument’s accuracy and range; for instruments with the same accuracy, an increase in the range also leads to an increase in the relative error ； ●When selecting a gauge, the maximum allowable error is determined based on precision and range, and it is converted into a relative error at the operating point; this value must meet the specified requirements ； ●Generally, when the operating point is between 1/2 and 3/4 of the range and the instrument accuracy is at least grade 0.5, it can meet the requirements of production. (You can tell by checking the pressure gauge and the plate level gauge.) ；

My personal understanding is that double flanges are just a type of connection method; when choosing such instruments, we usually consider the accuracy of the differential pressure transmitter. I’ve heard for the first time that double flanges also relate to accuracy – do you mean the manufacturing precision of the flanges?

Thank you for your answer. I have another question: suppose there are two ultrasonic flowmeters, one used for precise measurements and the other for general measurements – their accuracy levels will differ. But when one is not familiar with the process, how can one determine whether a measurement is precise or just approximate? The data provided in the process documentation usually doesn’t give any indications either.

In this case, it can only be determined by the accuracy of the instrument. In practical applications, try to avoid using two flowmeters to measure the same flow rate. Since errors are always present, having two units only makes things more confusing. Ultrasonic flowmeters have relatively large errors and are not suitable for accurate measurements.