dp cell quest

Hey guys... Using dp cell to measure vacuum pressure which is connected too the hp side n lp side is blocked off. My concern is when I tighten the plug on the lp side the dp changers....pls assist

Dp cell range is - 10kpa too 10kpa

Are you using an instrument manifold to connect to? or going right to the cell?.

I'd use an instrument manifold, tighten up all your connections, open the equalize port, then close it before applying pressure to the high side of the cell.

On a mechanical vacuum gauge, the bourdon tube is referenced to the atmosphere surrounding the bourdon tube.

To measure gauge pressure vacuum with a DP transmitter, like one would with a mechanical vacuum gauge on the manifold of car engine, connect the high side to the vacuum port and leave the low side of the DP open to atmosphere, because atmospheric pressure is the reference for gauge pressure measurements.

When you screw a plug into the low side on a DP transmitter, you are compressing the volume of air behind the plug, creating a false reference point.

-10kPa is only 3 inches of mercury (Hg), which is only 10% vacuum from atmosphere. That's a pretty 'light' vacuum. Are you sure you have enough range to measure the vacuum level needed?

If this is 4-20mA, 4.0mA will be -10kPa, 0kPa (atmosphere) will be 12.0mA, 10kPa will be 20.0mA

Theboss said:

Hey guys... Using dp cell to measure vacuum pressure which is connected too the hp side n lp side is blocked off. My concern is when I tighten the plug on the lp side the dp changers....pls assist

Dp cell range is - 10kpa too 10kpa

Click to expand...

10kpa to 10kpa is a very narrow range. They make devices with a wider range you may want to look into.

When measuring a vacuum (or suction) with a differential pressure gauge the L (low pressure) connection should be connected to the process and the H (high pressure) side should be open to atmosphere. I usually use a vent fitting on the H connection so that the port can breathe but dirt and such is excluded.

http://www.mcmaster.com/#vent-plugs/=t71gn0

I agree with you danw. Makes total sense.

Thanks to the rest off you gentleman as well.