Dear All,

I want to calibrate drum level DP transmitter for level control. Range has to take 0 to 8000 mmWc or -4000 to +4000 mmWc or give suggestion, more details & send PDF files on drum level control.

Regards,
Prashant Pagar

 

Hi,

A DP level measurement of a steam drum is about the worst possible application for DP level measurements conceivable. The density of the "liquid" and as a concequence the indicated level not only changes with the temperature but also with the steam pressure. This will require that you compensate the measurement with temperature and pressure measurements in order to calculate the level from the DP. Also You will have to make sure that both the impulse lines are allways completely filled with water. In real life this means that once you start up the boiler, it will take quite some time before the reading will become accurate. For all these reasons I would advise a different measurement principle for the steam drum level control. Anyway, it would always be a good idea to have a second and maybe even third independent measurement for such an important and safety related measurement. A middle of three would be the best way to go using three different measurement principles, e.g. DP, positive displacement, Infrared, mechanical with floating body, Radar if available in required temperature range...

 

David's advice is correct. There are a number of boilers and steam turbines here that use two indications(D/P and gap probes). Solutions here as listed below.

The questionable D/P type is for indication ONLY and is usually viewed by the operators and engineers as "maybe it's right".

Secondary, multiple-level(usually 3 levels: upper, middle, low) "spark plug"(point gap) type as the PRIMARY means of actually monitoring and controlling levels. The outputs of EACH are also feed to local, easily-seen(large) displays for operators to glance at and KNOW what's going on quick. They indicate levels in steps but a card in the 24A fieldbox can output mA for a simulated analog-to-DCS. Boilers and steam turbines cost $$$$$$ and can be LETHAL if not controlled properly. The newest units on the latest steam turbine are Penberthy/Tyco(we use 3 levels, vendor page only shows 1). Also, the 24A's we have display on their fronts AND repeat signals to single displays at convenient locations around the drums AND send to DCS:

Concept: http://www.penberthy-online.com/btp6.asp

24A JB/CP: http://www.tycovalves-na.com/brands_results.asp?Selection=Penberthy

Local Displays: http://www.penberthy-online.com/btp5.asp

NOTE: If you get these, keep very close tabs on the ceramic probes. We had one lost by a contractor's employee named "he don't work here no more"....probes cost about $450 each in May of 2003.

JC