Vibration Switch (Tuning Fork) 1

[jimpiper60777]

Hello to everyone!

Can anyone elaborate what vibration switch installed in a pipe is? In our project they call it tuning fork. And why it is installed in vertical pipe.

Thank you for your sharing.

jimpiper60777

 

[MortenA]

They seem to be referring to the level swith type that is commenly known as a "tuning fork" - because it works in much the same way. The fork will have e particular frequency depending on the medium.

I assume its used in vertical pipes as a type of flow swith - although i have never heard about this before.

Here a typical - i do not know this brand. It was a random google search.

http://www.omega.com/ppt/pptsc.asp?ref=LTU2000&ttID=LTU2000&Nav=

Best regards

Morten

 

[BigInch]

Its used in vertical pipes because that way it can work as a level switch. Supposedly it could be used in a horizontal pipe, but then it would be limited to levels bounded by the pipe diameter and normally you would want to know about the levels.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[jmw]

These are fairly basic sensors e.g. Liquiphant by Endress and Hauser and Squing by Emerson Mobrey.
They are driven at their resonant frequency which is a function of the effective mass of the system, that is, the mass of the sensor and the mass of fluid it is immersed.
There is a very substantial frequency shift when in air compared to liquid so they are very simply to produce as level switches.
Liquiphant:

http://www.uk.endress.com/

click: level, click: vibronic
Squing:

http://www2.emersonprocess.com/en-U...int-Level-Detection/Squing-2/Pages/index.aspx

VEGA:

http://www.vegacontrols.co.uk/vegaswing_vibration_liquids_index.asp

Ap Con Elixir:

http://www.sapconinstruments.com/vibrating-fork/liquid-level-switch.html

KTek:

http://www.ktekcorp.com/dnn20/Default.aspx?tabid=54&productTypeId=8

and so on.... lots to choose from.


JMW

http://www.ViscoAnalyser.com

 

[MortenA]

BigInch - level in a pipe? On a vertical line (normally "empty" e.g. a drain line) i could see it as a flow switch - and the of course on bridles. But i read this as "normal piping".

Best regards

Morten

 

[jmw]

Not sure how it could be used as a flow switch.

There is no flow effect on the resonant frequency.

There is sometimes a flow effect detected in the amplitude of the signal which is sometimes detected when using a fork for viscosity measurement and even though density meters take account for all sorts of extraneous effects like Velocity of Sound, Young's modulus, viscosity and so on (none of which is accounted for in a level switch, they look for a big step change), I am not aware of any significant flow effects being noted, but as a pipe empty/pipe full alarm it is ideal.

With some fork switches they can be tuned to detect interfaces between liquids if there is sufficient density difference, but in multi-product pipelines you would be inclined to use density zoning which calls for a much more sophisticated sensor.


JMW

http://www.ViscoAnalyser.com

 

[jimpiper60777]

Thank you so much for your replies.

 

[MortenA]

lmw: If its an empty pipe = no flow=air filled, then its one freq, if theres flow (of e.g. water) then its another.

Im just guessing - as the question did not only relate to: What is a tuning fork - but also: Why is it installed in a vertical pipe!

Its a switch (flow no flow) not a meter - but then again: Im just guessing i havent seen it myself.

Best regards

Morten

 

[jmw]

Morten, it can ceryainly tell whether there is fluid in the pipe or air but not whether that fluid is flowing.
I'll grant you that if the alarm state changes it must be due to flow having occured, but a steady state cannot tell you if it is still flowing (to the best of my knwoledge).

Note: a corilis meter measures flow by the phase angle shift and density from the resonant frequency.
So it measures flow but there is no correction to density for flow vene though there is a very accurate flow measurement signal available intrincisally within the same sensor.

A 1" tube density meter (vibrating element type) can be used across a rnage of flowrates from 0-40m3/hr without any flow correction to the density being necessaray. (accuraciess to+/-0.1kg/m3 so any flow effect would have to be more significant than that.


JMW

http://www.ViscoAnalyser.com

 

[MortenA]

That was why i said: I dont know the intention of the design - but i will try to relate to the original posters questions!

Anyway note that he states that its for a _vertical_ pipe! So without any further knowledge i said: It may be a "normally dry" pipe e.g. a drain but then again - jim has not added any info since his first post...

So maybe what i meant was a air/not just air

If he refers to the bridle on some vessel then i guess it just a standard installation for a level switch.

Best regards

Morten

 

[jmw]

I see what you mean, Morten, and I think it might have helped if we knew a little bit more about the installation and the relationship of the switch to other equipment.
In the flow/no-flow scenario it might be monitoring pump discharge where a centrifugal pump can drain back if it is off and if the switch is in a point above the normal drain down level then air means pump off and liquid means pump running.


JMW

http://www.ViscoAnalyser.com

 

[BigInch]

On or off, when the signal changes, a level crossed it. It can't ever tell you anything about flow.... unless you had two, knew how far apart they were, the x-sectional area of the pipe, timed the .....

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[jmw]

All you need of a flow switch is that it can tell you if there is flow or not.
OK, when, in my example, the pump stops you will have a short period when you think there is flow, and there is, but instead of being pumped forward flow it is now gravity reversee flow.
But if you needed better than that or you need flow measurement then you need something else.
These switches are real cheap. Maybe that's all that's needed.

Using two in series doesn't really help because even though you can infer the flow rate pushing the interface from one to the next, once its gone its gone.


JMW

http://www.ViscoAnalyser.com