Control.com - Nerds in Control

Dear All,

I am looking for some information on the DP transmitter connection for boiler drum level measurement. I am basically looking for if the steam and water side of the drum is connected to the high or low end of the DP transmitter and the reason.

I looked at various postings in the Control.com. I found the followings thread little bit useful but not so clear.
http://www.control.com/thread/1026228727#1342623072
This thread tell to connect the steam side to the high end of the transmitter and water side to the lower end of the transmitter.

I also looked at one of the article in EMERSON website: http://www2.emersonprocess.com/siteadmincenter/PM%20Rosemount%20Docume nts/00840-0100-4360.pdf

This article shows to connect the Low end of the transmitter to the steam side and high end of the transmitter to water side .This is also confusing.This article says the DP is maximum when the level is lowest and DP is minimum when the level is highest. It again says when the level is minimum the transmitter out will be 4 ma. So it is confusing . At the minimum level if the DP will be highest how the transmitter output 4 ma.This is really confusing.

Both the above information does not tell the reason why and which side of the drum (Water or Steam) needs to be connected to the high or low end of the transmitter. So I need all of your suggestion to clarify this.We are using Rosemount DP transmitter for drum level measurement. I have the following questions:

1. The steam and water side of the drum will be connected to High or Low end of the transmitter and why?

2. The DP will increase or decrease with increasing and decreasing level and why?

3. When the level is highest the DP transmitter output will be 20 ma or 4 ma?

4. Why to use the condensing pot in steam side tapping point?

Regards
Narayan

Steam side will have to connect on LP side, and water side on HP side.

Codensate Pot will provided at Steam side to fill DM water.

For drum:
1mm of water level = 1mm of WC.

Imagine that drum is empty. Now filled DM water on Steam side (Which is connected on LP side)

Now the pressure acting on LP side is higher than HP side because of the water filled by us in condensate Pot.(Because drum is empty)

Now DP transmitter will give Low reading (For example you are taken tapping points on 1000mm distance, the DP transmitter will give -1000mmWC, Similarly the range should be -1000 to 0mmWC)

If the water comes 50% of Drum, the DP transmitter will give DP as -500mmWC.

Actually the DP transmitter is giving difference between 2 water level. One is in Steam side,(The water filled by condensate pot)

One is water level. If the water goes to full, the difference between Water filled in Condensate pot, and drum is equal. SO DP tranmitter will give 20ma.

For above example -1000mmWC = 4ma
and                   0mmWC = 20ma (lly, Range is -1000 to 0mmWC)

Regards
Karthik