I recently added a tank to a SCADA system. The level is being sensed by a pressure transducer near the bottom of the tank. The tank is 32 feet in the center and about 29 feet at the sides. I'm told that it will actually fill all the way to 32 feet before it overflows but on testing it overflowed before it reached 30 feet according to my reading. I'm wondering how, if at all, the sloped roof affects the pressure at the sample point near the bottom. Anyone have any experience with this?

 

You don't really need experience. Just think about it. Head is head whether in a pipe or a swimming pool. The volume per foot will vary drastically, but the depth is the depth.

Regards

cww

 

Tank shape does not affect head pressure.

Specific gravity of the liquid, does, directly and proportionally. Levels are frequently referenced to the equivalent head of water. If your liquid is not water, then a conversion is needed to bring the indicated lewel in water head to the real physical level of whatever the liquid is at its specific gravity.

Any pressure applied in the vapor space above the liquid will affect the reading. If a vent allows pressure build-up (or allows vacuum) either will directly affect the pressure reading of a gauge pressure sensor. A properly plumbed differential pressure sensor compensates for this effect.

Is your liquid lighter in density than water? 32 physcial feet of something lighter than water could easily indicate only 30' of head of water.

Issac

 

Hi-

It sounds like you need to recalibrate your pressure transducer to give you the correct 4-20ma reading for your cut off systems. It also might be toast...

http://www.drlevel.com/conventional.htm

 

I recently added 2 sensors. One is lower sensor another is upper sensor. Here mainly i am introduceing PLC programming. When plc module is connected tank and execute the progrm the servo moter is started,then water level is increasing.

At the time bellow sensor sence the signlas. After inceasing the water level water reaches to second sensor then moter will stop.After when water level reaches to first sensor the moter will start. Like this procedure i can maintain water level in between two limits.

 

Thank you for your replies. Curt you were right, that's what I was thinking and I should have trusted that thought. My mistake was trusting my coworkers. They were right, the tank is 32 feet. However, it overflows at 29 feet. All equipment worked as it should, I just had bad info.