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Low Pressure Measurement

12/14/2016 1:14 AM

We are working for a Coke Oven plant.

REquirement is to measure 0.0004 mbarg pressure.

Could anyone help with the right instrument to measure the specified pressure?

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#1

Re: Low pressure measurement

12/14/2016 1:55 AM

How big the plant? Watch the airpressure gauge. It shifts more than that when a bird passes over.

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#2

Re: Low pressure measurement

12/14/2016 3:28 AM

Hi msn,

Are you sure of your units?

By my conversion app. it equates to "about" three ten thousandths of a millimeter of mercury!!!!

John

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#4
In reply to #2

Re: Low pressure measurement

12/14/2016 3:41 AM

...or 4μm of water or 4 picometres of air. Take the reciprocal: the atmosphere isn't 2.5e8m thick!

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#3

Re: Low pressure measurement

12/14/2016 3:32 AM

The requirement is unachievable; the variation of ambient pressure during the course of a day varies by a factor of 104 to 105 of that amount.

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#5
In reply to #3

Re: Low pressure measurement

12/14/2016 3:50 AM

Yes I am quite sure about unit of measurement. Even we are bit surprised looking at the application. We are trying to explore the methods to suit application.

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#6
In reply to #5

Re: Low pressure measurement

12/14/2016 3:54 AM

The requirement is unachievable. Therefore the application is nonsense.

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#8
In reply to #5

Re: Low pressure measurement

12/14/2016 4:39 AM

What are you smoking (or drinking)?

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#21
In reply to #5

Re: Low pressure measurement

12/15/2016 9:25 AM

Maybe this is the desired resolution of the instrument? Not the range...

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#23
In reply to #21

Re: Low pressure measurement

12/15/2016 11:55 AM

OTOH, the heading does read "Low Pressure Measurement." I can only assume from this and the figure cited, that 0.0004 mbarg is either the typical pressure the OP needs to measure or the sensor's full-scale range.

Perhaps if the OP was a little more forthcoming...?

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#7

Re: Low pressure measurement

12/14/2016 4:33 AM

Were you speaking instead of sound pressure level (SPL), 0.0004 mbarg corresponds roughly to an (RMS) SPL of about 66 decibels - about the same SPL as a loud conversation or driving at highway speeds with the car windows rolled down.

Now, even if you had this sensor, what's to stop the ambient noise level in your coke-oven plant from completely swamping your pressure measurements, possibly even pegging the sensor at the limit of its range? Do we assume 0.0004 mbarg is full-scale? If so, you would probably be measuring even smaller values in the normal course of whatever process you need this sensor for, no? Whatever it is, you'd better put it in a nice quiet sound booth or your measurements will be garbage.

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#9

Re: Low pressure measurement

12/14/2016 9:00 AM

Ridiculous!

Not possible and completely unnecessary.

Why would anyone need such a minute pressure variation indication in a coke plant, even if it were sound pressure?

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#12
In reply to #9

Re: Low pressure measurement

12/14/2016 11:32 AM

Whatever the OP wants this for, I hope it's not part of some process control loop. Plant noise aside, let's say a thunderstorm rolls into the area. A big thunderclap and that loop will go apeshit.

Ordinary garden-variety microphones routinely deal with far greater pressure swings, albeit at audio frequencies, but audible frequencies aren't the only game in town, especially at an industrial plant. Lots of low frequencies too. Infrasound. Might also need to isolate the sensor from vibration.

Let's say the OP averages the sensor readings to help filter out the acoustic component. That's all well and good but it isn't going to help much if the sensor is routinely pegged by high acoustic levels.

Somebody hasn't thought this through.

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#10

Re: Low Pressure Measurement

12/14/2016 10:57 AM

Looks like "we" will be not successful.

What coke requires this fine measurement? Is this a miniature coal power plant with a self driven CO2 sequestration?

I can hear a yes . . . damn pipe dreams . .

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#11

Re: Low Pressure Measurement

12/14/2016 11:15 AM

If, in the very highly unlikely event that Andrew Westman is correct about the real purpose of your request, here's what you will need.

Sound intensity probes - Brüel & Kjær Online Store

Even for the US this sounds nonsensical.

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#13
In reply to #11

Re: Low Pressure Measurement

12/14/2016 11:32 AM

They make nice stuff.

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#14
In reply to #13

Re: Low Pressure Measurement

12/14/2016 11:39 AM

Even if it were what the OP thinks they need, the price will quickly change their mind.

I was involved in active noise cancellation in the 90's. I'm sure the price has skyrocketed since then.

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#15
In reply to #14

Re: Low Pressure Measurement

12/14/2016 12:11 PM

Yep.

I was working a contract at TI for a few years near Houston. Running along the length of the building in which I worked was a very large, very long HVAC duct which terminated at a big plenum just on the other side of the wall near my desk. The thing acted like a giant organ pipe, but at infrasound frequencies.

There was a 'node' right where I sat at my desk. In the next cube over it wasn't especially noticeable, but right at my desk it was. I couldn't hear it so much as feel it but it drove me bonkers. Citing the problem I asked to move to a different desk. They sent a guy over from Maintenance; he couldn't hear it. Nobody else could either, but I could. They thought I was nuts.

To convince them the phenom was real I brought in a geophone that I happened to have, set it on my desk, and hooked it up to an oscilloscope. There it was, a big fat sine wave at about 12 Hz. Moved it to the next cube over and you could still see it but the amplitude was much smaller. Not only, but when the blower shut off the signal disappeared. Organ pipe.

I got my new desk.

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#16
In reply to #11

Re: Low Pressure Measurement

12/14/2016 12:56 PM

Might want to throw this in the mix for the OP as well. B&K's infrasound mic cartridge.

Sensitivity: 50 mV/Pa

Frequency: 0.02 Hz – 20 kHz (±3 dB)

Dynamic Range: 14.6 – 146 dB

Price: USD $2226

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#17

Re: Low Pressure Measurement

12/14/2016 3:55 PM

I spent 25 years in that industry and never had occasion to read pressures measured at that accuracy. What is the measurement being used for?

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#18

Re: Low Pressure Measurement

12/15/2016 12:10 AM

are you sure it is mbar not Mbar?

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#19
In reply to #18

Re: Low Pressure Measurement

12/15/2016 12:47 AM

Good point. A far more reasonable figure for a pressure sensor, to be sure, but why then would the OP frame it as a tiny fraction of a very large unit? 0.0004 Mbarg? Why not just say 400 barg? A question for the OP.

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#20
In reply to #19

Re: Low Pressure Measurement

12/15/2016 1:06 AM

Yes, exactly. Was it a typo on the drawing/specs, or did the OP not bother to hit the shift key and why bar anyway? Isn't the world using SI units? It seems to me that a more reasonable pressure to measure is just 0.0004 bar as in gas line pressure in cm of water. An explanation of the application would help. Jim

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#22

Re: Low Pressure Measurement

12/15/2016 11:08 AM

You say: "We are working for a Coke Oven plant."

Who is "we"?

Perhaps you can induce one of your associates to communicate the requirements for you?

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#24
In reply to #22

Re: Low Pressure Measurement

12/15/2016 12:07 PM

"I" am wondering how much time people have to stop by and post replies that doesn't make much sense.

people have problems if any such questions are asked.. Answers for which can be "Google'd" and there is a problem if people don't have answers!

as already clarified we were not sure abt the inputs we had and was trying hard to get some info.

thanks though!! ��

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#25
In reply to #24

Re: Low Pressure Measurement

12/15/2016 12:36 PM

So what IS your application? If you would be a little more forthcoming you might receive better replies, no? What a novel idea.

We are not there with you looking over your situation; you are, and so the onus is on you to put us there so that we understand the problem you're trying to solve and so can offer reasonable suggestions. Possibly the solution isn't something you've even considered, but if you don't tell us anything we're in the dark as much as you apparently are.

You've finally replied, but if you're making the effort to reply, why not also use the opportunity to supply more information. Is that asking too much? Possibly your efforts to google an answer have proved fruitless as well because you're not supplying enough info there either?

If you will not put more effort into this, why on Earth should we? We have nothing to gain from this, but you do. Is that not incentive enough to be more forthcoming?

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#26
In reply to #24

Re: Low Pressure Measurement

12/15/2016 12:48 PM

TALK TO YOUR INSTRUMENT SUPPLIER!

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#29
In reply to #24

Re: Low Pressure Measurement

12/21/2016 7:56 PM

Mistakes in units of measurement in posted questions are far more common, hence the large number of requests for clarification.

What you are basically asking for is instrumentation that can accurately measure medium level vacuum, so something like a McLeod gauge, or some other form of thermal or capacitive gauge.

McLeod gauge

Try a search of CR4's Globalspec site for US vacuum gauge suppliers or similar.

Let us know what you actually find that works. As others have said the measured value seems unbelievably low for the application.

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#27

Re: Low Pressure Measurement

12/20/2016 8:20 PM

Its a bit fresh and probably not made into a sensor, but this is what you are looking for.

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#28

Re: Low Pressure Measurement

12/21/2016 3:49 PM

My take on it is that the units are wildly incorrect.

0.004 bar (4 mbar) is 1.6 in H2O or 40.8 mm H2O, measured with a draft range transmitter

0.0004 bar (0.4mbar) is 0.16 in H2O or 4.08 mm H2O still measurable with a high end draft range pressure transmitter

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