SLC 5/04 - add floating point as online edit

[Operaghost]

The Usage file tells you what has been used and what is available by using a few different letters. It uses X, W, and F depending on the address and how it is being used in the logic.

When you open the input and output files, they are by default displaying the data in a binary format. So any bit that has been used will be displayed with an "X". However, you are not likely to use the bits on an analog module which is why all the bits do not have the "X" but instead have a "." meaning that bit has not specifically been used.

Instead you will likely use the entire word. So in the usage display under the "FW" column you will likely see a "W" indicating that a word type instruction is using the entire word. It is possible that a File-type instruction could use your analog value so you might even see an "F" in there. But that is probably less likely.

Now, on that display if you change back to viewing the data and then change the radix to decimal instead of seeing the sixteen bits for each word, you would instead see the decimal value that those sixteen bits represent. Very useful for analog! Now if you click Usage you will see the "X" displaying whether the entire word/element has been used regardless of Word or File type instruction.

Like I mentioned before there are still additional gotchas. Things like indirect addressing won't show up in Usage and if you have another PLC writing to memory locations in this PLC that won't show up either.

OG

 

[Doug W]

Thanks to everyone for all the suggestions and help so far. I have made a few changes in the program and although I am not getting the expected result yet in the DCS, (readings in the DCS that match with the real world pressure transmitters), I believe I need to do a little more reading and head scratching.

Thanks,
Doug

 

[Doug W]

Greetings,

Thanks to all who gave me suggestions on this problem. Things were sorted out today when I figured out that the old differential pressure transmitter had a range of 0 to 15" H2O and the new pressure transmitters were 0 to 25" H2O.

After I made the changes in the DCS and a second PLC that was getting the analog output via the DCS, the numbers matched the real world.

Mellis,

However, just a comment on the basic idea of using two pressure transmitters to replace a dP transmitter. It's often tried and rarely sucessful.

My memory was jogged by the recent cold weather here in Minnesota. We replaced the Diff. Press. Transmitter with 2 Press. Transmitters because one of the stainless tubes for the high side impulse line tended to get plugged from condensation and freezing in our fun weather here, so we ended up pulling the stainless line out and putting in a teflon line to get through the winter. Having separate transmitters allowed us to keep the tubing short and hopefully avoid the condensation/freezing syndrome.

Thanks,
Doug

 

[Lancie1]

Things were sorted out today when I figured out that the old differential pressure transmitter had a range of 0 to 15" H2O and the new pressure transmitters were 0 to 25" H2O.

I bet that whoever ordered those transmitters never thought that the 10" difference would have any effect on the PLC program, or that there was ANY reason to tell the guy trying to make it work! It happens all the time. I guess the moral of this tale is not to take anybody's assurance that "it will work" and check out everything personally.