Oneshot used with a latch

Hello everyone,

I just got a new project to implement where i will be converting a micrologix 1200 series plc program to a logix 5000 controller, don't know the controller yet.

Anyways i glanced at the already existing program and noticed oneshots used on the same rung in series with latch coils. Here is an example i demonstrated below.

Ex. Say you had a XIO called input then a oneshot in series with it and then anlatching output coil called output. The function of the one shot will make whatever comes after the one shot on for one program scan upon a false to true transition. Now if your output coil happens to be a latching coil(not to confuse this with a seal in latch) this kinda defeats the purpose of a one shot because although you have a oneshot, that latching coil if it happens to go true will indeed stay on even after the one scan.

So my question is and i know it depends on the application, but can this type of method be used to actually program a working logic and if so how have you used such logic?

I would use this method if I wanted the latch to SET only when the condition went from false to true.

Think of it like this:

|   INPUT    1-SHOT          INPUT 1-SHOT

|-----] [------] [---------------(  )

|

| INPUT 1-SHOT                  LATCH

|-----] [------------------------(S)

-Eric

dbh6,
i have seen this several times before but it has its downfalls. i replaced the oneshot logic with logic like my example. that eliminated all of my false triggers, data duplication to rsview, and false defects.

the purpose of the one shot is to prevent the latched bit from energizing after the second scan.

the downfall is that if the logic in front of the oneshot goes false to true, the latched bit will be energized again if it was unlatched, even if you didn't want it to. it all depends on what is in front of the oneshot.

what i do is have the rung conditions and have a bit b3:37 off contact and then latch in b3:37
conditions b3:37 B3:37
-----| |---------|/|------(L)

this is the same thing without the oneshot and b3:37 will not turn on again until you unlatch it first.

it took 2 days searching the program line by line before we actually saw what happened on the screen. an input turned off just long enough to see it.
regards,
james

Thanks guys appreciate it