I have used a DP transmitter with diaphram seal to measure Propane tank level. The level keeps changing from + or - 500 to 600 mm comparing to the sight glass. After venting the low side, the level becomes accurate and after 10 hrs again the level changes to 500 to 600 mm + or - starting from 10mm gradually. Can any one help?

 

What shape is the tank? Sphere? Vertical cylinder? horizontal cylinder?

What's the level when full? 15m, 10m, 50m?

What brand and model transmitter? How old is it?

Are either or both of the high or low sides of the transmitter fitted with diaphragm seals and capillary tubing? Or is the diaphragm seal you refer to at the end of an extension tube that fits into a flanged spud? Or some other style?

If seal/capillary, what is the length of the capillary tube that connects the diaphragm seal to the transmitter body? What is the fill fluid?

What is the ambient temperature at the times you are comparing level readings? Same temperature?

What do you mean by "after venting the low side"? Even at winter (assuming you're in the northern hemisphere) ambient temperatures, propane develops a healthy vapor pressure which cannot, literally vented off. More gaseous propane will vaporize to replace that which is released during "venting".

Does "venting off" release any liquid propane from the low side?

As a percentage of full level, at what level did the xmtr reading match the sight glass "after venting" 30% full? 50% full? 80% full?

David

 

Thanks for your concern.

>What shape is the tank? Sphere? Vertical cylinder? horizontal cylinder?

VERTICAL CYLINDER

> What's the level when full? 15m, 10m, 50m?
> 3.5M
> What brand and model transmitter? How old is it?

ROSEMOUNT 3051S

> Are either or both of the high or low sides of the transmitter fitted with diaphragm seals and capillary tubing? Or is the diaphragm seal you refer to at the end of an extension tube that fits into a flanged spud? Or some other style?

DIAPHRAM WITH fLANGE AND CAPLIARY TUBE.
FULL SET FROM ROSE MOUNT

> If seal/capillary, what is the length of the capillary tube that connects the diaphragm seal to the transmitter body? What is the fill fluid?
> 3 MERTERS.FILL FLUID SILICON OIL DENSITY 0.95
> What is the ambient temperature at the times you are comparing level readings? Same temperature?
3TO 4 DEG C SOME TIMES MORE TILL 20 DEG C
>
> What do you mean by "after venting the low side"? OPEN THE VENT PORT AND RELEASE THE GAS.

Even at winter (assuming you're in the northern hemisphere) ambient temperatures, propane develops a healthy vapor pressure which cannot, literally vented off. More gaseous propane will vaporize to replace that which is released during "venting".

> Does "venting off" release any liquid propane from the low side?
YES SMALL QTY

> As a percentage of full level, at what level did the xmtr reading match the sight glass "after venting" 30% full? 50% full? 80% full?

CLOSE TO 50%

ARUL

 

> What shape is the tank? Sphere? Vertical
cylinder? horizontal cylinder? <

Vertical cylinder.

> What's the level when full? 15m, 10m, 50m? <

3.5M

> What brand and model transmitter? How old is it? <

Rosemount 3051S

> Are either or both of the high or low sides of the transmitter fitted with diaphragm seals and capillary tubing? Or is the diaphragm seal you refer to at the end of an extension tube that fits into a flanged spud? Or some other style? <

Diaphragm with flange and capillary tube. Full set from Rosemount.

> If seal/capillary, what is the length of the capillary tube that connects the diaphragm seal to the transmitter body? What is the fill fluid? <

3 meters. Fill fluid silicon oil density 0.95

> What is the ambient temperature at the times you are comparing level readings? Same temperature? <

3 - 4 deg C, sometimes more till 20 deg C

> What do you mean by "after venting the low side"? <

Open the vent port and release the gas.

> Even at winter (assuming you're in the northern hemisphere) ambient temperatures, propane develops a healthy vapor pressure which cannot, literally vented off. More gaseous propane will vaporize to replace that which is released during "venting".
>
> Does "venting off" release any liquid propane from the low side? <

Yes, a small qty.

> As a percentage of full level, at what level did the xmtr reading match the sight glass "after venting" 30% full? 50% full? 80% full? <

Close to 50%

ARUL