Using electromagnetic flowmeter
measurement of molten metal fluid needs to follow the basic principles of electromagnetic flowmeter is a kind of using range is very wide range of flow measurement instrument, with the deepening of the technology and the increase of the actual demand, the variety and model of electromagnetic flowmeter with diversification, not only measure the low class liquid, there are measuring various fluid varieties resistant to acid and alkali solution and other extreme, I'm here today to introduce is a kind of electromagnetic flowmeter can measure under the molten state, and the electromagnetic flowmeter in such high temperature medium basic measurement principles and the related key points needing attention.
Using electromagnetic flowmeter measurement of molten metal flow is a typical example of high temperature fluid measurement.
With other fluid in this case, it is not the same situation, choose the basic principles of electromagnetic flowmeter induces has the following two points: 1.
Structure is very simple.
Maintenance free and high reliability.
The principle of clear.
Rarely in the flow on the output signal, and can produce factors of traffic signal control.
* item first pointed out that in principle there is no obstruction of the flow of factors, in fact not only can ignore the pressure loss, and the output signals are obtained theoretically.
That is, the output signal is only dependent on the strength of the magnetic field and pipe geometry, such as to master the art of has determined, measured on the key is to completely control the magnetic field.
That is to say, the current body of physical parameters on output hardly impact: the other principle of the structure of the flow meter.
But this kind of situation, especially the flow meter of actual flow calibration takes a lot of costs.
Because there are practical difficulties, therefore, very much hope is avoided this item also can finish the work.
Through theoretical analysis of the measured output, small diameter flowmeter has been figured out.
Output and flow between the linear damage, give theoretical treatment increased the difficulty.
However, this theory also can be applied directly.
In addition, its structure has the following three parts: 1 itself constitutes a flow, with insulated pipe bender can stainless steel tube;
2 on the wall, in two locations with tube center symmetry with the welding method installation of cable 3 formation of magnetic field of magnetic field devices.
So the structure is simple.
And in the use of magnetic field devices and permanent magnets, without any external auxiliary energy output signal can be obtained.
From the above may safely draw the conclusion: even for measuring metal rong melting, also use the same as the piping material form the flow meter.
So, the high temperature flow design basically do not have any special attention to item.
So this kind of flow meter is of high temperature molten metal processing and the theory of the electromagnetic flowmeter, the structure of the two issues together.
The details of its research results collected in Japan machinery institute survey report, here only related special matters.
Trial production of electromagnetic flow meter for measuring liquid metal structure, mainly by the magnetic field generator varies according to purpose are the following four.
With a permanent magnet type furnace channels.
Process with a permanent magnet type.
Process with large diameter dc saddle shaped coil.
Furnace with eddy current differential velocity type.
6 a, b, c, d shows and the four kinds of purposes in corresponding charts, the I and 4 kinds of used for furnace, including magnetic field device of the flowmeter is exposed to high temperatures.
On the contrary, 2 and 3 kinds of used for furnace, magnetic field device is limited to low temperature.
The following simple description of these four magnetic field device.
On one occasion by permanent magnet and pipeline into concentric rings and sheet forming strong magnetic field.
Magnet, aluminum nickel and cobalt alloy sheet with pure iron.
For use under the high temperature of 500 ℃ or so, so you should have after the formation of magnetic circuit, reduce the induction with temperature change and the non reversible change, in the hot, dry heat treatment under high temperature.
In the combination of the two, the temperature of the magnet itself can close to room temperature, therefore, don't need the special treatment.
However, in order to reduce the magnetic flux leakage, play to the performance of the magnet, magnet to form available combinations.
In contrast to 2 3 kinds of need external power supply, etc.
Sometimes flux correction device, but fewer restrictions, magnetic structure design degrees of freedom.
4 and in the past, the principle of structure is different, it is developed according to the differential transformer, its purpose is to detect detect near its velocity, the liquid metal with the theory of electromagnetic flowmeter, detailed in Cleveland's writings.
In the practical, the output with the E type said: E = K1 * K2 * K3BDV here, for the magnetic induction (B
Wei tube inner diameter (D
The average flow velocity (V wei fluid
K1 for pipe wall output short-circuit effect correction coefficient;
K2 for magnetic fluid end of short-circuit correction coefficient;
K3 for tube expansion correction coefficient.
No matter the occasion, on the principle of pipe material are magnetic, electrical conductivity is lower than the fluid.
So, using the same as the piping or thinner austenite stainless steel pipe.
In order to good to make contact with the liquid metal, in addition to carefully deal with the inner surface, and 3 welding, inspection, etc.
In section 2.
Remove the signal wire, used in the furnace, but with the MI cable, outside the furnace, can use ordinary steel wire.
However, from the perspective of reduce error caused by thermoelectric emfs, require the conductor and line is the same material.
In this paper by embellish instrument technology co. , LTD. Arrange release.
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