In my plant we are equipped with 3(2o o 3logic)DP transmitters of Rosemount type:3051L2AG0XC31AAS1M5Q4 with one remote seal of type:1199MDB10AFFWG1DA00. The thing is that in a period of 5 years we've changed them all due to instability & inaccuracy driven by membrane damages. Our seals are repairable welded "M" and not all welded vacuum which means that in such high vacuum applications it can be considered reasonable to be damaged so frequently.

Checking manufacturer's manuals I found out that we can not be provided with all welded vacuum seals since these can be combined only with 3051T,2088 or 3051S and not with 3051L which is our case. So we are thinking of replacing them but don't know which would be the best solution?

Checking the web I can see that also microwave radars are considered reliable?

 

Hi there,

You need to replace those type L transmitters (completely wrong type for vacuum) with the 3051CD2A with capillaries and remote seals. The HP pad cell(remote seal) will connect to your current connection and the LP pad cell will connect to a point higher up or on top of the vessel where there is only gas and no liquid. You also need to order flushing rings the same ID as the padcell flanges and tapping point pipe, otherwise you will not be able to flush the tapping points during calibration. This is very important to do so don't even order them unless you order the flushing rings as well.

I have use these capillaries in various high pressure as well as high vacuum applications and no problems. Very accurate and reliable once they are setup properly. If someone tells you capillaries drift that is twang, it is 99% of the time just that person that don't know how to work with capillaries.

The only draw back with capillaries is to find someone to calibrate them since they are not straight forward to setup.

Actually in vacuum applications the capillary type is easier to do than a piped wet leg installation (also possible to do but not my first preference) so yes definitely go for the capillaries. The supplier will help you to select the correct type of remote seals once you told him what you want to use it on. You just need to find a place higher up or on top of your tank/condenser to mount the LP seal before you order them.

Even better than the capillaries are the Guide Wave Radars (GWR) or the Frequency Modulation radars (the micro wave radars you referred to - called the TDR technology radars - Time Domain Reflectometry). My preference would be the guide wave type radar but the draw back again is finding someone to set them up. Very difficult if you have never worked on them before. I have very good experience on the Khrone BM100A and can recommend them for your vacuum application. I would also recommend you specify the "A" since that means solid rods type. They are also flange mounted so again you need to see if you have some place to mount them on top of the vessel first before you order anything. To find the probe length(rods length) measure from the bottom of the flange to about 50mm from the bottom of your vessel and specify that as the probe length you require.

The FM radars are easier to setup and will also work unless the product is very turbulent inside your condenser. The advantage is that both radars types are not influences by pressure, vacuum, density, foam, emulsion or any of the normal problems. You will set them up once and forget about them for the next couple of years.

If all else fail and you just cannot find any place to mount the flanges of either the capillaries or the Radars, I am sure you can find some place on top of the vessel to screw in a 1/2" fitting or tap off from another piece of tubing with a T-piece. In which case you can go for a normal piped instillation and a wet leg. Not easy to do but if you work carefully and accurately it will work fine and is reliable enough, if no one fiddles with it after wards.

If you get stuck with setting up either the capillaries, the radars or the wet legs, let me know.

 

You need to be specific about the vacuum level and service, also what range of level are you measuring. Diaphagm failure can be due to many reasons. Since you need a specific vendor response, you need to contact them, they have access to far more resources available than listed in the catalogs.

 

Thanks a lot Sam,

That was for sure a comprehensive view for the total understanding of the system.

We are let's say focusing in microwave radars and had a very interesting portfolio presentation of E+H for same successful applications in other power plants.

The only thing is that we have to order them most probably directly with their bypass pots so as to be attached directly to our flanges.
Otherwise we have to manufacture them "in house" but I would be more confident with an original supplier design.

What's your opinion?

 

Hi again,

I am not to sure about these "by-pass" pots you are referring to since it can mean various things. The units I used only had the flange attached to it and you attach the complete unit to the flange on the vessel or stand pipe.

The bypass I think means a extra piece of pipe where only the cone or rod is attached and then you have a removable head. It might be a good idea but in my opinion you should remove the complete unit once or twice a year and inspect it anyway so it might only come in handy if the head fails.

 

Is your voting logic for safety reasons or just to get a useable process reading?

If safety, you might want to experiment with the alternative technologies before putting your safety on the line with them.

 

To the last Bud post,

Nothing wrong with using a voting system on these transmitters. We use the voting system in various locations on highly critical applications(for exp. the HIPPS).

Keep in mind you don't want a complete plant shutdown or deluge just because a transmitter failed. The voting system prevents that. The same thing on the safety and Fire and Gas systems. There the voting system is used on just about everything so in general it is in most cases better to use a voting system and I think it is just cost that prevent the design engineers from doing it in more places.

You are welcome to let us know about the alternative technologies you are referring to.