DL330 psuedo one shot pulse

Caledonian

Member
Join Date
May 2009
Location
Tasmania
Posts
2
Hi all,

I'm currently porting a program from a DL330 based PLC to a micrologix 1200. It looks like the original programmer has coded a sort of one shot pulse:

|---| |--------------|/|------------------------------( )--|
| |
| Momentry_PB PB_log_coil 1_shot |
| |
|---| |-----------------------------------------------( )--|
|
| Momentry_PB PB_Log_Coil


*edit*: well my text based representation didn't come out so well but you get the idea...

So as the cpu scans through the rungs the first rung is energised. As soon as the second rung is scanned it switches off the output of the first rung, so the output stays on for no longer than a single scan of the ladder.

Now, as there is a one shot pulse function available in the DL330 instruction set, can anyone think why it would be coded this way? Is it just a programmer a bit set in his/her ways and unwilling to try out these new fangled functions or is there something a bit more sinister happening.

I only have a 24 hour period to get the new plc installed and working so I want to make sure the program is right before I go for it.

Cheers!
 
The first Series One CPU, which the DL330 is a successor to, did not have a one shot in its instruction set. That function didn't appear until the Series One Plus. Your program could be a legacy from those days.

Your understanding of the operation is correct. There is no reason not to use the MicroLogix one shot instruction.
 

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