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barg and bara
Continuous process industries, DCS questions. topic
Posted by Anonymous on 16 November, 2006 - 11:45 pm
I want to know the difference between barg and bara. how can I convert them?


1 out of 1 members thought this post was helpful...
Posted by Steve Linehan on 18 November, 2006 - 6:25 pm
BarG - (Gauge Pressure) Pressure reading relative to current atmospheric pressure.
BarA - (Absolute Pressure) Pressure reading relative to absolute vacuum.

i.e. If a tank has a positive pressure of 350 mBar and the atmospheric pressure of the day is 1006 mBar then the readings would be.

BarG = 350 mBarG
BarA = 1356 mBarA

There is no conversion from BarG to BarA as atmospheric pressure changes from day to day but the range of change is about 50 mBar. If you add 1000 mBar to a BarG reading then it will convert to BarA but will be +/- 50 mBar.

Steve Linehan


Posted by saiful islam on 6 July, 2014 - 2:17 am
so is 1 barg = 1 bar?


Posted by Michael Batchelor on 18 November, 2006 - 6:26 pm
Bar(Gage) is relative to local atmospheric pressure, while Bar(Absolute) is relative to absolute pressure. How to convert them depends on the local atmospheric pressure.

MB
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Posted by instrumania on 18 November, 2006 - 6:29 pm
bar a = bar g + 1


Posted by Anonymous on 18 November, 2006 - 8:57 pm
Bara (Absolute pressure) is a pressure mode where the reference pressure is absolute zero, i.e. not taking into account atmospheric pressure (which is approx 1 bar), where as Barg (gauge pressure)is referenced above atmoshperic pressure.
Thus the difference between an absolute pressure value and a gauge pressure value is the variable value of atmospheric pressure:

Absolute pressure = gauge pressure + atmospheric pressure.

Hope this helps.


Posted by denn on 18 November, 2006 - 8:59 pm
Barg = Bara + your local atmospheric pressure in Bar's

Dennis


Posted by senthil on 16 May, 2008 - 2:27 am
Hi sir,

I think you are wrong.
bara = barg+ atm pr.

Is it correct?


Posted by FX Bambang Budi H on 21 November, 2006 - 10:09 pm
barg means bar-gauge (gage)
bara means bar-absolute (including atmospheric pressure)
bara = barg + atmospheric pressure (Atm),
if 1 Atm = 1 bar,
bara = barg + 1.
Is it answer the question?

best regards,
FX Bambang


Posted by Roy Matson on 16 May, 2008 - 9:32 pm
Some of you seem quite confused. The first few posts got it right, went down hill from there.

Bar Absolute is not related to atmospheric pressure at all, it's related to absolute vacuum, e.g. if you have a pressure of 1.2 Bar Absolute it doesn't matter what the atmospheric pressure does, it's still 1.2 Bar Absolute.

Your weather report calls out the atmospheric pressure in Bar Absolute so you know the pressure of the atmosphere related to an absolute vacuum.
The pressure of the atmosphere is always zero Bar Gauge at sea level or 20,000 feet, wet or dry.
An altimeter (traditional) is a pressure gauge that measures the pressure related to absolute vacuum. The reading is effected by the weather. An early way to measure elevation was to boil water and measure the temperature it boils at.

If you see a pressure in Bar it's Gauge, you don't need to add the "G". A pressure gauge reads Gauge pressure. An absolute pressure transmitter is like a DP cell with the low pressure side under a perfect vacuum. We use them on evaporators to keep the conditions constant no matter what the weather does.

Hope I haven't added to the confusion!

"I'm sure this thread is going to be a long one".

Regards,

Roy


Posted by cheme on 26 July, 2008 - 1:32 am
I am a little confused. If I have a vessel that operates at atmospheric pressure, then what should I see on a pressure gauge???

= 0 barg??? or ~ 0.01 barg???
Also, I don't quite understand, when people refer to bar, they meant to say bara???


Posted by Roy Matson on 27 July, 2008 - 12:04 pm
Cheme,
If they say bar, kPa, psi, or just about any other pressure unit you should assume it's gauge, If they mean absolute they should say so, adding a g is redundant and annoying.
Just remember a pressure gauge reads g pressure.

There are some units that are based on absolute e.g. Torr

On your vessel you will see 0 bar, 0 kPa, 0 psi 0"WC etc.

Hope this helps
Roy


Posted by Vallaban on 5 November, 2009 - 2:21 am
For getting the approximate value while converting bar g to bar a then bar a = bar g + 1.02. That 1.02 is 760/750.......1 Bar = 750 mm of Hg & 1 Atm = 760 mm of Hg.


Posted by Bruce Durdle on 5 November, 2009 - 1:51 pm
Or you can use the standard value of atmospheric pressure - 1.01325 barA.

But if you are interested in "approximate" values, use 1 barA. Anything
better and you really need to start looking at the actual value of
atmospheric pressure at the measuring location.

Cheers,
Bruce


Posted by 1441q- on 22 December, 2010 - 11:37 pm
i have one question,
how to convert barg to bar?

e.g : 1barg = ?bar


Posted by curt wuollet on 23 December, 2010 - 2:13 pm
Since bar gauge is implicitly referenced to atmosphere they should be equivalent IIRC.

Regards
cww


Posted by Anonymous on 10 August, 2007 - 8:47 pm
bar a = barg +1
:-)


Posted by rajesh on 18 January, 2011 - 3:40 am
>I want to know the difference between
>barg and bara. how can I convert them?


Bar gauge pressure and bar absolute pressure...

gauge pressure = absolute pressure - atmospheric pressure.

atmospheric pressure is normally 1.013 bara

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