Tank Level off Pressure Transmitter

Hi All,

Just wondering what the best/most accepted way to measure tank level off pressure transmitter. Pressure transmitter is located in line with the outlet (0m).

4-20mA PT also has Zero and Span buttons.

My 2 methods i can see:

• Take PT out of tank and press Zero. Return to tank and fill to overflow, press Span.
• Take PT out of tank and press Zero. Using Druck pressure pump calibrator, pressurize PT to known value above tank overflow eg: 5m, and then calculate Zero-100% (4.3m) in code.

Cheers,

Your first option will probably be the best if it's possible, as it is a simple procedure that can be done by any random tech.

Is the PT fitted to the actual outlet pipe? You can get issues with high flow rates resulting in headloss in the pipe and giving you falsely low readings. Its best if located on a static point at the bottom of the tank.

In saying that we have a number of >1000m3 water tanks with level sensors on outlets, and it's only an issue when there's a mains break somewhere.

Your first option is fine, we also just use a tape measure when it's an externally visible overflow. Give yourself 20-30mm of freeboard up the top as a minimum.

Do you know the density of the fluid? Does it change? Why not calculate it?

Is a block and bleed valve manifold out of the question for both your methods? Close block, open bleed, when drip stops, press zero. Place pump in bleed connection, pump to desired pressure, press span.

How often would you need to do this calibration that a HART communicator wouldn't be the best alternative?

Do you have an overfill protection device?

thanks for the responses everyone, Approx 200kL water tank. Density probably doesn't change too much. The pressure transducer is opposite side of the tank to the center of outlet (process 0% full) but at the same height.

Overfill protection is a digital float, plus overflow to dirt.

The PT manifold isn't bleedable, but PT can be removed while powered up.

I think I'll go with option A for ease, but option B sounds better for 'correctness'..

I was wondering why I was getting really minimised values when it was first installed.. the installers filled up the manifold with silicone ���� the water must have been pushing against it and the compressed air fluctuation on the PT side of the silicone was being measured lol

moistcat said:

I was wondering why I was getting really minimised values when it was first installed.. the installers filled up the manifold with silicone ���� the water must have been pushing against it and the compressed air fluctuation on the PT side of the silicone was being measured lol

Click to expand...

That's inconsiderate of you... they added a protection diaphragm free of charge. /s

You should have seen the look on our faces when we removed the PT to inspect, then one of us opened the manifold valve, and no water came out.. (with about 5m head on it)
We drilled out about 7" of silicone!?!?