Questions about the transmitter
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Yesterday, while reviewing the instrument specifications, I found that for the EJA transmitters: 1) The model is EJA430A-EMS5A-87EB, with an accuracy of 0.075; it is a pressure transmitter. 2) The model is EJA118W-EMSH4BA-BA02-97EB, with an accuracy of 0.2; it is a double-flange level transmitter. The selection guidelines provided by the EJA manufacturer also indicate this accuracy level. My understanding is that the accuracy of level transmitters can only reach 0.2. (It consists of two flanges.) I would like to ask everyone a question here: For example, on the electrolyzer, there is a pressure transmitter for hydrogen pressure and another one for chlorine pressure; both of these transmitters are of the EJA type, so their accuracy should be 0.075. However, in terms of control requirements, we need to keep the differential pressure between hydrogen and chlorine at 2.5 KPa. Does this mean that the accuracy required in this case is also 0.2? In other words, it’s not possible for the differential pressure in each electrolyzer to always be exactly 2.5 KPa, but it can be within 2.5 KPa plus or minus 0.2, right?
I really don’t understand what you wrote ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
I finally understand now; the original poster didn’t explain things clearly enough. Here’s what it means: if you want to keep the measured value at 2.5 KPa, then that measured value isn’t accurate, as there will be fluctuations. In other words, when the differential pressure is 2.5 KPa, the actual measured value isn’t exactly 2.5 KPa, but rather it varies by up to 0.2% either way. . Since it floats proportionally, the impact isn’t that great actually!
Accuracy, also known as precision, refers to the degree of consistency between the measurement result and the true value of the quantity being measured. The accuracy of a transmitter is expressed in terms of the maximum allowable error, indicated as a percentage. When selecting the accuracy of a transmitter in use, it is determined based on your application requirements. Generally, the maximum allowable error of the transmitter should be less than 1/3 of the error tolerance required for your process. If the requirements for process accuracy are not high, but the transmitter used has very high precision, it is pointless and represents a waste of cost. The requirements for level measurement are not very high from a process perspective; a transmitter of class 0.2 is sufficient. It’s not necessary to use only transmitters of class 0.2 – using a transmitter of class 0.075 would be a waste.
This post was last edited by nmgwang*n36 on 2013-5-3 at 14:25. The pressures of hydrogen and chlorine in the electrolyzer are both controlled via their respective pressure control valves, with the aim of keeping the pressure difference between them at 2.5 KPA. However, the pressures of hydrogen and chlorine are measured by two separate pressure transmitters, each with an accuracy of 0.075. So, what is the accuracy of the measured pressure difference: 0.075 or 0.2?
It’s obviously 0.075, but system error also needs to be taken into account. . . . . . . . . . . .
The precision for a single pressure transducer is 0.075; if measurements are taken using multiple instruments, then system errors must be taken into account, which is the square root of the sum of the precisions of each instrument~~~
Personally, I think the accuracy should be 0.15, as with two 0.075 pressure transmitters, one gauge may have a positive error while the other has a negative error.
The precision should be the square root of the sum of two values of 0.075 squared.
The precision of 118 does not reach 0.075 ； 110 and 430 are okay