Differential Pressure Gauge

A1) Yes, though such a device is uncommon. If onward transmission is not required then a simple sight glass might fit the bill, for example.

A2) In order to interchange pressure and level one needs to know the density of the liquid. Density varies with temperature.

A3) There are maybe more than a dozen ways of measuring the level of a liquid in a tank. The correct one to select depends upon the application, which is a function of many variables that are not presented in the original posting. Preference is less applicable than appropriateness in this regard.

Thank you PWSlack. I will anticipate another solution, probably a sight glass.

Or a dipstick, perhaps?

Or, some common sense, if any is available.

Good point.

A differential pressure sensor or a sight glass requires that the tank be empty while the lower connection port is inserted, which may not be practical when retrofitting. If you need to fit the level indicator while the tank is still in service, using a single access to the roof of the tank. A float with a top rope, led over a pulley mounted on the top of the tank, to a weight on the outside of the tank. As the float rises, the weight lowers against an inverted calibrated scale, allowing the level to be read directly.

Please advise if level measurement is further used for volume calculation or is the pressure in the tank that is of interest?

With a conical bottom the volume calculation needs further processing if pressure or level is being used.

Level measurement will not be furtherly used. Actually, only the local level indication is needed.

See first post then and follow up!

DP obviously can not get to true empty point if you are doing batches. On process water tanks that are never emptied, we use them regularly. For batches, to do a conical bottom to true empty point, you can use a guided wave radar or capcitive rod and bend the rod to follow the contour. Linearity then is obviously violated when the liquid falls into the bent portion. We always transmit to a PLC and this creates some real "fun" programming the non-linearity created by the bent rod. On just an indicator system, extrapolation of the data (readout) can be done and recorded so you know where the fluid truly is in the tank.

Nothing beats sight glass, as it works well during power outage too.

Other than that, I would use one differential for actual measurement, another for an "almost empty" warning, both local and remote reporting.

If the tank is completely and freely vented to atmosphere, then a mechanical gauge pressure pressure gauge can be used. The cheapest gauges do not have removeable dials, but mid and upper level gauges have dials can be removed and custom silk screened with a scale that is appropriate. The dial below is a custom dial:

The scale must take into account the specific gravity of the medium, as mentioned earlier in the thread. If the medium's specific gravity changes, the gauge error is proportional to the SG change.

If the tank is pressurized, there are mechanical DP gauges that could be used, typically a diaphragm gauge. Same deal, the DP range is selected and the dial has to be custom silk screened.

In the US, the custom silk screening is done through gauge distributors, not the manufacturer.

http://www.ittbarton.com/page15.html
Contact them with your requirements, stating the tank fill-height and fluid density. They will be able to produce the level measurement onto the standard DP scale, or provide you with sufficient info to mark it up yourself. www.ittbarton.com/

If as PWSlack mentioned the density is stable then a PDI is a good option, but remember, the location of it as well as any contaminants can foul the sensing lines.

Most gauge manufacturers can make specialty gauge scales in pressure or level, as long as you give them the detailed information.

Since the Gauge is generally below the sensing line location you have to take into account the hydrostatic pressure due to the location of the gauge.

You did not indicate if the tank is a closed vessel where you would need a PDI, if its atmospheric you could use a PI with the range equivalent to the height of the tank times the density and include the hydrostatic head due to location of the gauge.

It appears, that since #9 note there is a divergence in language, what is assumed factual.

In that note, I insisted on one local, mechanical indicator that works even during power outage.

And two differential pressure silicon sensors. One for measurement, one for empty/near empty reporting.

I may be off the mark. But, is not the instrumentation drifting toward mostly electric?