one shot OSR and Res

[Guest jack]

can any one explain what the one shot do (osr) ive read what it does but i didnt fully understand it, anther question, do we USUALLY need to reset timers , i know we use reset for counters alot but for timers do we need to reset it thank you jack

[JimRowell]

Jack, A one-shot is a term used in electronics to describe a timer that doesn't reset itself. When it's triggered, it begins timing. When the preset interval expires, it switches its output and then sits there forever until reset. The term has been hijacked by a couple of plc manufacturers to refer to similar things. AB has an instruction called OSR which stands for "One-Shot Rising". You use it to monitor the status of other devices. When the monitored device goes high, the OSR bit will go active for one program scan only. This way you know if something has "just now" changed. Similar to Mitsubishi's various pulse commands. As for timers and more specific help, you really should ask in the AB group (if that is in fact the plc brand you are interested in). Jim Rowell