DP Gauges with Negtive Range

This arrangement will work just fine as a vacuum gauge, I do it all the time. Or, for getting a specific range, try these people, and use their gauge finder:

http://www.dfs-gauges.com/GaugeFinder.aspx

Perhaps I don't understand the complexity of your problem, but Omega (and I'm sure many others) sell DP units with field selectable ranges.

www.omega.com

It would be helpful if you tell us what you're trying to do.

If you connect a dp (differential pressure) gauge or transmitter with the high port to atmosphere and the low port to the vessel being measured, your reading will be positive if the pressure in the vessel is less than the outside pressure. If the pressure in the vessel is higher than the outside pressure, your reading will be negative.

Should you use a vacuum gauge? It depends on your application. If you're measuring the pressure inside an evaporator, you should use a vacuum gauge (which is referenced to absolute pressure). If you're measuring, say, furnace internal pressure, you should use a dp gauge since you want to make sure that the furnace internal pressure is less than the outside pressure.

"furnace internal pressure is less than the outside pressure"

Furnace pressure should always be MORE that ouside pressure, about .05" H20 WC, anyway. This prevents cold air from entering the furnace, which would ruin your uniformity.

Hmmm, we must be talking of different furnaces then.

In our factory, we have heaters that we maintain at a slightly negative pressure with respect to atmosphere.

I'm not at liberty to say what they are but suffice it to say that if the application requires that you maintain a differential pressure between two areas or spaces then use a differential pressure gauge. If the application requires you to know the actual pressure (with respect to absolute pressure), use a vacuum pressure gauge.

All of our furnaces are run at a slight negative gauge pressure, no more than a couple in. H2O, but still negative. I think we use regular Rosemount transmitters, I'm not aware of anything particularly special about them.

I believe what you are looking for is called a compund gauge. They are readily available.

Hi!

I think you should check up Rosemount guys (www.emerson.com/rosemount) - they have a model (I think it is called 3051 CD0) just for such applications....