Three typical wrong installation ways of electromagnetic flowmeter
Author:vacorda Source:vacorda.com Date: 2018-05-09 15:33:49
Electromagnetic flowmeters are the commonly used measuring instruments in sewage treatment and chemical engineering industry. Many friends may encounter a variety of problems: unstable flow values, inaccurate flowmeters, and frequent flowmeter damage. So how to solve them?
The accurate selection is very important, but more importantly are the wrong installation ways of the electromagnetic flowmeters
Problem 1: Large fluctuations with flow rate
At a certain site, the value of the customer's electromagnetic flow meter has been fluctuating.
At the site there is a pump next to the flow meter. The fluid is in a turbulent state (that is, the water swirls) when passing through the flowmeter. In this case, the flowmeter is subject to greater disturbance during measurement, and then occurs the phenomenon.
When installing the electromagnetic flowmeter, keep it away from the pump and at least 5 times the distance from the straight pipe section to ensure fluid stability.
A similar case installed near the valve▼
Problem 2: The flow rate is always inaccurate.
On the customer site, flow measurement is always inaccurate, and sometimes there will be empty pipe alarm and lower limit alarm.
From the above image, we can see that only half of the pipe is less than water, which means that the electromagnetic flowmeter is not full at all. How can this be measured accurately?
At the outlet of the flowmeter, install a section of the pipe to extend it and reduce the diameter so that the liquid fills the entire pipe.
Problem 3: The electromagnetic flowmeter is often damaged
This electromagnetic flowmeter is installed under the water, and the instruments may cause the damage. Generally, the enclosure of the electromagnetic flowmeter is IP65, it can support rain protection, and cannot be soaked.
it is recommended to use the IP68 protection class. If the on-site pipe does not support reducing the diameter, the sewage can be concentrated and then the pipe can be re-plied. After the pump is used, the flowmeter is installed. Or change to ultrasonic open channel flow meter.
Why is electromagnetic flowmeter measurement so strict on installation requirements?
1. The electromagnetic flowmeter measurement principle is mainly based on Faraday's electromagnetic induction principle. The conductive medium cuts the magnetic induction wire to generate the induced electromotive force, and the two measuring electrodes installed on the central axis of the pipeline collect the signal.
Let’s look at the analysis of the first case. The measured water may not have passed through the measuring electrode, and no signal is completely sensed. The flow meter naturally displays a lower limit alarm or an empty tube alarm. So, the it must need the full water of the pipe.
Under what circumstances can water guarantee full pipe?
Vertical pipes, water from bottom to top, certainly full of friends, of course, there is also a horizontal pipe installation method. So that the flow of the pipe in the selected range, the flow is certainly accurate and stable.
2. The flow through the flowmeter in the pipeline should be uniform and stable. Because we measure the flow, which is actually the product of the flow rate and the cross-sectional area of the pipe. The flow rate is unstable and the flow will naturally jump.
Let’s look the analysis of the second case, the pump is near the flow meter, the first to rule out high-power instrument interference with the product signal, the flow rate is certainly unstable, so our conventional choice is to install the flow meter as far as possible. Of course, one of the most important things, a long straight pipe is needed!
The role of the straight section is to smooth the flow rate of the fluid so that it can flow evenly and stably through the flowmeter. Then continue to read with me, straight into the paragraph, the first ten five, the first ten five. (It means that the flowmeter must have 10 times the straight pipe section in the upstream direction and 5 times the straight pipe section in the downstream)
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