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Measure boiler level
have to measure boiler drum level of 500 mm

good morning,

we have to measure boiler drum level of 500 mm. We have seal pot on upper leg i.e. steam side. Now what will be setting of transmitter. we are using honeywell smart type transmitter STC9000 series.

Hi there,

Need more info,
What is the distance between the top and bottom tapping points on the drum? (mm)
What is the distance from the bottom tapping point to the position below the bottom tapping point where the transmitter is installed?(mm)
Do you have the HP leg connected to the bottom tapping and the LP leg to the catch pot already?

Double check the model number of the transmitter. The STC9000 series does not exist. I need the correct info to see if the tx is the right size.

Our transmitter is 3000 series of honeywell make. n model no: STD-120-E1A.

distance from two leg is 500 mm. HP side of transmitter is connected to bottom flange of drum level where as condensate pot is connected at LP side of transmitter at above flange of Boiler drum i.e. steam side. Boiler Drum is on First floor and Transmitter is mount on ground floor. So impulse lines come horizontally side by side to transmitter. What configuration we have to use in transmitter?


Hi again,

Sorry for the slow response but I had to do some traveling for two days.

The transmitter you currently have is to big for the application. (0 to 400inchH2O = 0 to 10000mmH2O). You also did not send me the information I requested. I still need the distance from the bottom tapping point (HP connection) to the point where the impulse lines go into the transmitters.(at the moment)

This is a critical application so you cannot use a transmitter that is more or less the right size. The whole installation have to be right otherwise you will not get accurate and reliable readings and also with a small span like this any imperfections will be amplified when you put the transmitter on line.

I am also considering another thing that will improve accuracy, response and reliability, and that is to move the transmitter closer to the bottom tapping point and use a much smaller transmitter. Can this be done? Can you get hold of a smaller size transmitter? I think about a 0 to 2000mmH2O will be perfect for a application like this but then you need to move the transmitter to about +/- 1000mm below the bottom tapping point. Will this be possible?

I also need to know if the bottom tapping point on the drum is zero and the top tapping point is 100%. If not you need to send me the distances measured from the tapping points where zero and 100% must be.

You also need to have a look at the display unit if it is setup for direct measurement since in the old days we use to change the HP and LP legs around and then the display unit were also turned around to accommodate the 20 to 4mA signal. So in this case there is no need to change the LP and HP legs around, since you use a smart Tx, so the display unit must also be setup to take a direct measurement (4mA = 0% and 20mA =.100%)

Your installation seems to be done right. Only thing that feels wrong is the catch pot on the LP side. You say it is installed above the top flange? Might still be ok to use it like that but the side outlet of the catch pot should actually be going to the top flange and the bottom outlet of the catch pot should be connected to the LP impulse line. The top of the catch pot will be slightly above the flange.
If the catch pot only have a bottom entry (therefore it is above the flange with a T-Piece to connect to the flange and impulse line) then we will use it as it is installed at the moment.
Send me more detail about how the catch pot is installed and the actual size of it as well.


I am measuring the drum level 0-920mmWC. My transmitter range set is +620 to -320. So, the high side tapping is at +620mm & low tapping is at -320mm from the NWL. So, i had erected the seal pot at +970mm elevation. So, can i measure the range 0 to 920mmWC or not???

You can make any measurement you want and it is not influenced by where you installed the catchpot. The purpose of the catchpot is just to keep a constant head on the one side of the transmitter. Once you know what this reference value is you can set the calibrated zero and span on your transmitter to anything within its capability. The closer this span is to the actual capability of the transmitter the more accurate your transmitter will be.