Boil Drum - Level Transmitter Range

I WORKED BEFORE IN STEAM POWER STATION AND I REMEMBER THAT THE NAGATIVE LEVEL OF THE DRUM IS RELATED TO DATUM LEVEL (ZERO LEVEL) UNDER IT THE INDICATOR SHOWES THAT THE LEVEL IS IN NEGATIVE

SO THE TRANSMITTER IS CALIBRATED NORMALY BUT THE INDICATOR IS ADJUSTED TO SHOW NEGATIVE LEVEL

FOR EXAMPLE:IF THE LEVEL TO BE MEASURE FROM 20MMW TO 200MMW SO THE ZERO OF THE TRANSMITTER WILL BE 20MMW AND THE SPAN IS 180 ( 200-20) & THE ZERO LEVEL (DATUM) IS 90MMW .ABOVE THIS LEVEL THE INDICATOR WILL BE POSITVE BUT BELOW IT THE INDICATOR WILL BE NEGATIVE

I HOPE THIS HELPS YOU

BEST REGARDS

Hi there,

First - Pressure = Height x Density X Gravity (P=HDG)

Now - temperature and pressure have an affect on density.

The pressure and temperature in your boiler steam drum are not 100% constant. So your density is changing all the time, even by small amounts.

The temperature of your impulse lines (the takeoff lines going to the transmitter) are at a different temperature to the temperature inside the drum - so you have a density change.

As you can see from the above formula - this will in turn affect your level reading i.e. the accuracy.

The solution would be to have temperature(density) and pressure compensation to offset these affects. This would in turn give you a much more accurate reading but at a higher cost.

You would need three pressure transmitters and a temperature mesurement of the liquid in the drum. P1 placed at the lowest point of the drum. P2 Placed at a fixed point midway up the drum (P2 to P1 gives you a known height) and P3 at the top of the drum.

Now you have a fixed height, temperature and pressure compensation if you use the following formula: P1-P2/known height = density (density compenstation)

P1/compensated density = level i.e no more fluctuations or offsets.

Regards,

Craig

Hi I m Bikash ,working in a 600 mw boiler drum. There are 3 d/p s 3 temp transmitter. I want to know why we use transmitters like this???? plese anyone help to solve this question......

Hello

out of three drum level LT ,one is used for alarm purpose and average is taken for other two LT in three element control in DCS.

Sushil