Electromagnetic flowmeter can flow for accurate measurements, the characteristics of fluid medium in the pipeline to effect on the measurement data is particularly large, especially if you can't do it with tube measurement, even do not have enough fluid flowing through the electrode, flowmeter can't do it work properly.
This article mainly aims at the pipe conditions to make analysis of the fluid.
According to our engineer experience, summed up down from fluid cause electromagnetic flowmeter failure mainly include: 1, the gas in the liquid, 2, liquid containing solid, 3, uneven conductivity of liquid 4, contact material matching misconduct, 5, and flow noise.
The following five aspects about the cooperate with our actual case make specific instructions: 1, the dissolved gas in the liquid to gas in the liquid will not affect the flow measurement, free gas (
The bubble)
Will affect the measurement and may cause failure.
Free gas in the liquid source has three aspects: (1) the pipe air not net, (2) from the suction piping, (3) dissolved gas conversion.
Before the two previous section has been mentioned, the latter because of liquid caused by change of temperature and pressure.
Below the liquid at room temperature, for example, static retention period in the pipeline,
Such as parking)
, the dissolved air could be converted into bubbles;
Above room temperature liquid static cooling contraction in the sealed on both ends of pipe, the formation of partial vacuum, or dissolved air gasification steam bubble.
Such formation of air bubbles in the process to drive the initial stage output sloshing phenomenon, often can appear to run for a period of time that is normal.
Control valve opening is very small, easy vaporization liquid gasification, sometimes also can form bubbles.
2, in the liquid to liquid containing solid powder, particles, or fiber, such as solid, failure may be produced are: (1) slurry noise, (2) electrode surface contamination, (3) insulation sediments or sedimentary cover or lining, electrode (4) the lining by wear or by deposition, change the circulation area.
Case 7 conductive deposits short-circuit effect electromagnetic flow sensor measuring pipe insulation lining surface if deposited conductive material, traffic signals will be short circuit and instrument failure.
Because of conductive material is sedimentary gradually, this kind of failure usually will not appear in the debugging stage, and to run a period after the show.
A diesel engine factory electrolytic tool workshop where the cutting process test device, with DN80mm instrument measurement and control of saturated salt electrolyte flow in order to get better cutting efficiency.
At first the meter running, continuous use two months later, feel the flow display value more and more small, until the traffic signal is close to zero.
On-site inspection, found a thin layer of yellow rust deposit on the surface of the insulation, wipe clean after the instrument is running normally.
Yellow rust layer is caused by a large number of iron oxide deposition in the electrolyte.
This example is a run-time failure, although not see more failures but if black metal pipeline corrosion is serious, sedimentary rust layer, also can have the effect of short circuit.
Who started running normal, over time, the flow shows more and more small, should be analyzed with the possibility of such failure.
8 cases of silt deposit Shanghai huangpu river upstream water from more than 30 kilometers to the rectangular pipe water diversion, again to two DNl600mm pipe pumping raw water into the factory, with two DNl600mm electromagnetic flowmeter metering of water.
Opened in 1991, the use of normal, but feel measurement to reduce to 1993, through inspection ruled out the instrument open part of the cause of the problem;
Check the asymmetry of flow sensor of resistance of these two electrodes, the analysis of flow sensor failure probability, because can't stop to check the hidden part.
1997 April afternoon to have the opportunity to entering the pipe internal condition, check the flow sensor tube wall thick silt place for more than 10 mm, electrode surface is covered by the silt deposit, flush with the surrounding silt layer.
After shoveling scrub, instrument operation is back to normal.
Confirm the cause of the problem is due to deposited silt internal pipe wall.
According to this instance, the flow of raw water measuring meter channel wall always deposited silt, whether affect measuring just the length, in this case the water quality conditions run 3 years has felt the flow measurement value decreases.
Electromagnetic flowmeter for measuring river raw water must be regularly cleaned.
Other flowmeters, such as ultrasonic
flow meter and mercury tube flowmeter have at least the same deposition reduce circulation area, problems, affect the measurements accuracy of triangulation DNl600mm tube deposit 10 mm 1 flow value will change.
2% 2.
5%.
Run for a long time what should be considered in engineering design at the same time the influence of deposited silt countermeasures, such as: improve the measurement velocity to extend cleaning cycle;
Presets into tube cleaning inspection hole, etc.
This example is a common failure 3 run-time, electronics has a tendency to within the liquid injection ratio of non-uniform flow & quot;
Dosing & quot;
Fluid, and injection liquid reciprocating pump is commonly used to join.
If injection liquid and the main liquid conductivity is different, the mixture mixing, electromagnetic flow sensor if its downstream, because of the rapid changes in conductivity can make the instrument output, while the liquid conductivity is greater than the threshold value and slow change will not affect the normal measuring electromagnetic flowmeter.
This phenomenon in feed water treatment project in the process of raw water to add coagulant is frequent.
4, contact with the liquid material matching improper contact with the liquid parts material produces matching fault with electrodes and improper grounding ring.
Match the misconduct in addition to the corrosion problem, mainly is the electrode surface effect.
Surface effect are: (1) chemical reaction (
The surface passivation membrane, etc. )
, (2) and electrochemical polarization (
Produce potential)
And (3) catalysis (
Electrode surface generating aerosol, etc. )
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