PSIA vs PSIG

[ptonsparky]

Well, I ordered the wrong one :rant: and I haven't figured out who to blame. What I wanted was PSIG with 4-20 ma and 0-15lbs working pressure. 4-6 is my working range.

What I ordered was a 4-20 ma transducer that gives me 18.47 ma @ atmospheric pressure. Looks like I have another spare part on the shelf unless someone can tell me how to scale it out with only 1.53ma to work with

 

[don_resqcapt19]

That would depend on the instrument...often the manufacturers use the same instrument for multiple ranges. You will have to look at the details and see how much you can change the range of the instrument. If you can range it to ~14.7 to 29.7 it will do what you want.

 

[ptonsparky]

That would depend on the instrument...often the manufacturers use the same instrument for multiple ranges. You will have to look at the details and see how much you can change the range of the instrument. If you can range it to ~14.7 to 29.7 it will do what you want.

I went cheap...not this one. $160+-. I could set it up to tell them when it is time to change air filters on their blowers.

Max PSIA is 30 but 15 gives me the 20ma.

 

[hurk27]

What brand is it? Rosemounts generally can be rezeroed at 14.7 and span set to 29.7 which would give you a 0 to 15 psig transmitter as long as you have a hart protocol communicator to reset the zero and span to read 4-20 from 0-30psig at the above settings, Rosemounts generally use the same pressure cells for a range of transmitters, we have 100 psg rated cells that we use for 0-30 inH2O that work just fine, look at the cell max pressure if it is over 30 psi then you should be able to reset the zero and span.

Even without the hart communicator most transmitters have a way to set the zero and span under the cap or under the slide away plate on the top, it will look like a aluminum spec plate with a rivets but one end will slide off and there will be push buttons or small pots to adjust the zero and span or they might be inside the from cover on the display side older Rosemounts were pots under the aluminum plate, look for a cap, plug or buttons marked zero, span or might just have a Z and S by it.

Also you might be able to order a 0-15psg replacement cell, I would talk to your suppler, the electronics are all the same for a range of cells you just have to have a hart communicator to reset the 14.7 psia to 0 psig unless it has buttons on the transmitter to program it.

At $160+ I would suspect it is not a Rosemount as they are much higher in price, normally I see them around $500 to $700

If you post the manufacture and model I might be able to look up the info you need?

 

[GoldDigger]

You have an additional problem beside just range.
One way to build a pressure gauge is to measure the motion of or force on a diaphragm.
If it measures PSIG, one side of the diaphragm is open to atmospheric (or other ambient) pressure. The reading will be the difference between the duct pressure and atmospheric pressure.
If the transducer measures PSIA, then one side of the diaphragm will be at a vacuum, and the reading in the duct will change with changes in atmospheric pressure.
Since the pressure on the low side of the filter may change depending on downstream restrictions, what would be best would be a differential pressure gauge which would connect to both sides of the filter.

Sent from my XT1080 using Tapatalk

 

[ptonsparky]

Model #628-00-GH-P9-E1-S1 Dwyer from Grainger.

A plugged filter was about the only thing I could remotely come up with for its use. Grabbing at straws.

 

[Smart $]

Model #628-00-GH-P9-E1-S1 Dwyer from Grainger.

A plugged filter was about the only thing I could remotely come up with for its use. Grabbing at straws.

Is there a reason you cannot return it, or exchange it? I don't know the exact manner in which your went through your ordering process, but Grainger lists <link> that as a 0-15PSI model. No 'A, no 'G in the advertised spec's. In the instrumentation craft, a product is assumed to be PSIG-rated where the fourth letter is omitted. Compare with info on another model on their website with slight variation in model sequence number, only difference is P1 rather than P9 as the fitting spec': <link>

For future reference, the series model listing...

http://www.dwyer-inst.com/Product/Pressure/SinglePressure/Transmitters/Series626-628/ModelChart

 

[ptonsparky]

Is there a reason you cannot return it, or exchange it? I don't know the exact manner in which your went through your ordering process, but Grainger lists <link> that as a 0-15PSI model. No 'A, no 'G in the advertised spec's. In the instrumentation craft, a product is assumed to be PSIG-rated where the fourth letter is omitted. Compare with info on another model on their website with slight variation in model sequence number, only difference is P1 rather than P9 as the fitting spec': <link>

For future reference, the series model listing...

http://www.dwyer-inst.com/Product/Pressure/SinglePressure/Transmitters/Series626-628/ModelChart

That is what got me in trouble. Assuming it was what I wanted. I didn't see anything in the Grainger specs that said A or G either. Both times.:ashamed1: I sent the first one back because it didn't work. I had this little voice in back of my head saying "investigate further" but I ignored it until the second one did not work as expected either.

I usually order from AD and they were out of the one I wanted. I ordered a 0-10v model instead of the 4-20ma.

Another one of Life's educational moments.

 

[GeorgeB]

I could set it up to tell them when it is time to change air filters on their blowers.

Max PSIA is 30 but 15 gives me the 20ma.

That Max PSIA of 30 is without damage ... your model is 0-15 psiA for 4mA to 20mA. The 18.47 says your atmospheric pressure at the time is (18.47-4)/(20-4)*15, 13.56 psiA. That's really low for a sea level pressure ... what's your elevation.

For filter clogging, what you want is a differential transducer, reads the difference across the media.

 

[GeorgeB]

Since the pressure on the low side of the filter may change depending on downstream restrictions, what would be best would be a differential pressure gauge which would connect to both sides of the filter.

+1; AD has a series of differential transmitters at reasonable prices, but they don't get nearly that high. With AIR filters, I'm accustomed to pressure drops clean under 1 inch water, dirty under 2 inch water. Those are WAY under even 1 psiD, D== differential. 1 psi is roughly 2 feet water column (27.7 is closer, but technically depends on local gravity.

Their DPTA-20-25 is 25 inches water, or about 1 psi. On a 24*24 filter element, that would be about 600 pounds force!

 

[ptonsparky]

That Max PSIA of 30 is without damage ... your model is 0-15 psiA for 4mA to 20mA. The 18.47 says your atmospheric pressure at the time is (18.47-4)/(20-4)*15, 13.56 psiA. That's really low for a sea level pressure ... what's your elevation.

For filter clogging, what you want is a differential transducer, reads the difference across the media.

Last I knew I was above sea level. About 2200'

 

[Smart $]

That Max PSIA of 30 is without damage ... your model is 0-15 psiA for 4mA to 20mA. The 18.47 says your atmospheric pressure at the time is (18.47-4)/(20-4)*15, 13.56 psiA. That's really low for a sea level pressure ... what's your elevation.

For filter clogging, what you want is a differential transducer, reads the difference across the media.

Last I knew I was above sea level. About 2200'

13.5psia or thereabouts is reasonable at 2,200fasl. It will vary with barometric pressure.

 

[Cmdr_Suds]

It will vary with barometric pressure.

Yes, very much so. 1 in-Hg = 1.13 ft-Wc so if the atmospheric pressure changes from 28.5 in-Hg to 31.5 in-Hg the you output will change over 3 ft-Wc without the actual measured value changing. Your calibration and readings will literally vary with the weather. Not very useful if you need accurate measurements. I once found an absolute transmitter installed on a water tower and the owner could not figure out why some days the tower would overflow and others not.