Can any one tell me the formula to calculate ttxm in 9E gas turbine for mkvie based control system and give a brief note on spread calculation?
The exact formula for deriving TTXM is in the application code running in the Mark VIe controlling and protecting your GE-design Frame 9E heavy duty gas turbine. There should be a block with a name similar to Thumbnail, where the 'n' is a number which denotes the revision of the block. If you right-click on the block and then click on 'Block Help' (sometimes it's 'Item Help') a most file should open to explain what's happening.
Briefly, the formula usually rejects values below approximately 500 definitely F when the unit is running and then averages the remaining values. Pretty simple. I believe some TTXMVn blocks also reject the highest and lowest values; to be sure you need to review the block used in the Mark VIe at your site.
The exhaust temperature spread calculation is also usually performed in a block, with a name similar to TTXSPVn. And you can usually access a help files in the same manner. Briefly, the block usually does some sorting and arranging of the values in order to arrange them from highest to lowest and then check to see if the highest and lowest values are adjacent(next to each other). Some blocks check for hot spots and some for low spots in the exhaust; it usually depends on the type of combustion system. However, in contrast to the TTXMVn block the TTXSPVn block does NOT usually rejects any values, as that would defeat the whole purpose of the Combustion Monitor. (It's this one little difference that usually causes the most misunderstanding.)
The best way to know how the Mark VIe at your site is accomplishing these functions is to review the blocks used in the application code running in the Mark VIe at your site and not rely on any other written description as it may or may not be applicable to your site.
If you are having specific issues, try to describe them here and we will try to answer or explain them. Most of the time issues are perceived because of misunderstanding the application code running in the Mark VIe at your site.
Hope this helps!