Questions and Answers about Electromagnetic Flow Meter Measurement Data Failure

Q: What is the reason for the inconsistency between the electromagnetic flowmeter measurement data display and the automatic control room display?
The flowmeter installation meets the installation requirements (installed on the riser to ensure full pipe), and the automatic control room range is consistent with the flowmeter range. The flow displayed by the industrial computer in the automatic control room is 3-5m3/h more than the flowmeter on site. The cable uses rvvp shielded cable.
 
A: First check the current output of the flowmeter. Directly measure the flowmeter terminal, then check the current input terminal in the main control room cabinet, compare the two to see how big the difference is. Then convert it to flow and compare it with the flow difference. Then calculate the error value according to the accuracy level and flow measurement range described on the flowmeter nameplate or manual. If the current difference is within the error range, you don’t need to consider its fault problem and continue to run. The third is to install a model isolator to isolate the interference of external high-power electrical appliances. The fourth is to consider the length of the signal cable. Although the current signal has a long transmission distance, it still has a certain attenuation, but compared with the voltage, the attenuation is much smaller. The fifth is to look at the conversion accuracy of the DCS or PLC card.
 
Q: Are the measurement accuracy of electromagnetic flowmeters with different calibers and the same accuracy consistent? There are
two Yokogawa electromagnetic flowmeters with the same accuracy, one with a large caliber (DN200, measurable range 11-1100), and one with a small caliber (DN80, measurable range 1.8-180). When used to measure the 100 flow condition, is there any difference in the difference between the measured value and the true value of these two flowmeters? In other words, which one is more accurate, the larger one or the smaller one, or are they the same?
A: Instrument errors are generally divided into two types:
1. Relative accuracy, generally expressed in %, which means relative to the accuracy of the full range of the instrument, that is, the accuracy of the instrument is: range x%, the larger the range, the lower the accuracy.
2. There is also absolute accuracy, which is the resolution of the instrument. This is generally unrelated to the range.
When the flow velocity in the flowmeter is less than 0.3m/s, the measurement error of large and small calibers is the same (1mm/s). When the flow velocity is greater than 0.3, the standard accuracy is based on 0.35% of the flow velocity.      That is to say, as long as the flow rate is controlled to exceed 0.3, there is no difference in measurement error between using a large diameter or a small diameter.