Ti PM550 conversion to standard ladder

Hi,

Can anyone offer me some Ti assitance?

CR230 CR240 CR 300
|----) (---*---)/(--------------------------------( )--
| |
| |
| CR300 |
|----) (---
|
|CR 300 ______ CR240
|----) (------|SF |--------------------------( )---
| |P |
| |C610 |
| |______|



Special Function 7
Compare two numbers
Start address: C610 next address: C615
Error output?......Y
Error output designator:,,,,,CR450

Location of first word (A) to be compared:……..V100
Location of second word (B) to be compared:....C130

Compare functions
Permitted:

1=A less than B
Etc
5=A Greater than B

Compare function requested:…….5
Status designator:…………………CR280
Chain special function…………….Y

My understanding is that CR230 pulses on and maintains itself through CR300.
When the SF is completed, CR240 energises and unlatches CR300.

My query is the status of the CR280 flag when the function is completed, for the remainder of the scan and the next scan?
From my experiment, in standard AB ladder code, it would seem that my following conversion is incorrect. Can anyone enlighten me? Do I need to use a latch bit for the CR280?

CR280 is used here but will never be on!
|---) (--------
|
|
| CR230 CR240 CR 300
|----) (---*---)/(--------------------------------( )--
| |
| |
| CR300 |
|----) (----
|
|CR 300 _________ CR280
|----) (------|Grt |--------------------( )---
| |A:V100 |
| |B:C130 |
| |__________|
|
|CR 300 CR240
|----) (--------------------------------------( )-----


Sorry for the poor ladder insert, I did look for some tips on this.

Thanks

Ben

NOT SURE

See if this makes sense

Follow up.. Helpful

Siemens were most helpful, this was their reply, at least its proved my conversion is incorrect:

I'm afraid I no longer have a PM550 to work on, and my memory cells are going but here goes ...

CR280 is set true when the comparison operation has executed only if V100 is greater than C130. CR240 is set true anytime the SF has executed successfully regardless of the outcome of the comparison. If CR280 is set true, and the comparison is then *not* performed on subsequent scans, nothing in this code will turn CR280 off. Simply because the SF is not called (i.e. CR300 is false) does not mean CR280 will automatically change state. In order for it to change, the SF must be executed again, and the result of the comparison must be false. The SF could be called, CR280 set true and stay true for a considerable period, even if the values in V100 and C130 have changed. It will only be on a subsequent execution of the SF that the change of V100 and C130 could result in CR280 being set false.

In your second piece of logic the same pattern applies. While CR300 is false, no comparison is done, therefore no change of state to CR280 is made. Whatever state CR280 is given by the result of the comparison will be retained until the comparison is next performed. So CR280 will change state only on a periodic basis when the check is done, not instantaneously when the values of V100 and C130 change.

I have seen a similar piece of code used to try to provide some delay in alarm detection and indication. Is CR280 an alarm indicator? If it is set true at any time, it will stay true at least until CR230 comes true again. This may be a timed pulse every few seconds. Similarly, short deviations of V100 with respect to C130 will not cause it to come on unnecessarily. This is quite crude, but simple.

Finally, is it possible that CR280 is also being controlled elsewhere in the program? There could be other logic which decides when to turn it off while the comparison is not being executed.

I hope that's been of some assistance.