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How to calibrate DPT for boiler drum level control - calibration method at field without manometer as well as lab calibration method with menometer. How to decide range of DPT?

The drum level transmitter generally uses hydrostatic head method of measurement. The span is regulated by the length of the static leg in inches of water.

Calibrate with a manometer or similar source. Verify by raising and lowering water level (within a safe range while boiler is in operation) and record the transmitter output.

Well, if you use differential pressure transmitter like Siemens sitrans P DS III (for example9 you can use blind calibration option. Just reliable measure distance between "+" and "-" impulse pipe. Note that "+" pipe inserted through condensation pot on the steam side of a drum. When you know that, for instance, distance is 500 mm, than just calibrate your transmitter 4 mA=500mm and 20mA = 0.

Then, in software (PLC or DCS) you make correction regarding working pressure and temperature and perform offset. Usually, drum level is between some negative and positive value. With offset you declare zero and have level from -250mm to 250 mmm (just for example).

Now, in regular service maintenance works, you can check transmitter by connecting it to the water column and test its linearity.

Regards

Steam drum level calibration is not something you should attempt unless you really know what you are doing. Don't attempt it unless you have a boiler or process engineer verify your calculations. If you already have a set of figures that don't seem to make sense don't just assume that someone made a mistake, there might be something going on that is not obvious.

There are several different ways of connecting the DP cell to the boiler. If you post a sketch someone will be able to give you some better pointers. However, I think you are asking how to simulate the level once you have the correct figures. If you don't have a manometer you can easily simulate the pressures with a couple of lengths of clear plastic tubing filled with water, Use larger diameter e.g. 1/2" to avoid errors due to bubbles. The LP tube will be fixed at a height to simulate condensate pot and you will raise and lower the HP tube to simulate the change in level (remembering that this side is effected by drum density).

I have attached a link that shows some of the errors possible.

http://www.tycoflowcontrol-na.com/ld/180.pdf

G oogle "Steam drum level" and you will find lots more.

Hope this helps.

Regards,
Roy