BSR in Logix5000

[Daryl 1]

Hi folks. I'm just recently learning bit shift registers, and although I'm understanding what they're about, I'm struggling to apply the knowledge. I've been going through a massive learning curve over the last 6 months or so, and I'm struggling to retain interest in the learning part, although I'm due to take a break from studying for the next few months so I can begin to apply the things I'm learning, but right now, I'm struggling with the bit shift register instruction. I understand that the shift right and shift left is moving a bit through an array, no problem, I get it. However, I'm not sure how to apply it, how to control it, and just as importantly, where to apply it. I'd appreciate if someone could provide the simplest of examples and explain how each instruction and tag is being used and controlled. thanks in advance... Daryl

[Chris Elston 79]

Daryl, I wrote an article about BIT SHIFT LEFT. http://www.mrplc.com/kb/index.php?article=71 Most of the time engineers will use this to track a process. The article describes how to apply it.

[Guest]

basic idea: a sensor at ONE point on a conveyor line tells you "what-to-do" to a certain part on the conveyor line ... BUT ... you can't actually DO the required action – until the part reaches ANOTHER point further down the conveyor line ... SO ... you need to REMEMBER the required action by setting a bit (like writing a "remember-to-take-this-action" note) - and then SHIFT that note along with the part as the part moves down step-by-step through the conveyor line ... THEN ... when the part (along with its "remember-to-take-this-action" note) finally reaches the ACTION point on the conveyor line, you have the PLC examine the bit status and then take the prescribed action ... FOR EXAMPLE: suppose that a sensor at ONE point on a conveyor line tells you that you need to DISCARD a broken bottle ... BUT ... you can't actually discard the bottle – until the bottle reaches the KNOCK-IT-OFF-THE-BELT point further down the conveyor line ... SO ... you need to REMEMBER to DISCARD the bottle by setting a bit (like writing a note) - and then SHIFT that note along with the bottle - as the bottle moves down step-by-step through the conveyor line ... THEN ... when the bottle (along with its "remember-to-discard-this-bottle" note) finally reaches the DISCARD point on the conveyor line, you have the PLC examine the bit status and then actuate a ram to discard the bottle – by knocking it off the belt ... SUMMARY ... you set a bit (either ON or OFF) as dictated by the status of a sensor ... then you use either a BSR (Bit Shift Right) or a BSL (Bit Shift Left) to "TRACK" the ON or OFF status of the bit step-by-step down the conveyor line – keeping in time with the step-by-step motion of the part down the conveyor line ... using a BSR or BSL is usually "dealer's choice" ... in other words, choose the one that makes more sense to your human mind – the PLC doesn't care about "left" or "right" ideas ... FINALLY ... read the information under the heading "Bottle Line Simulation – Applying Bit Shift Instructions" at The Learning Pit website which can be reached by following the link shown below ... www.thelearningpit.com - Traning Resource Page I hope this helps ... PS Edit ... I see that Chris is up early too ... Edited 1 Apr 2011 by Ron Beaufort

[dmargineau 6]

The most common application for the Array Shift instructions BSR (BSL) is keeping track of "different" elements within an intended "identical elements" fixed length batch. For example a fifteen station production line inspects for quality compliance after Station 5. There are no provisions for removal of the defective products until Station 10. A Length=5 Array will "load" a "true bit" at position one of the array every time a defective product is sensed at Station 5. A good product will load a "false bit" and so on. By shifting all the array's bits in one direction after every product inspection step is completed, the position of the defective product (true bit)is tracked through the stations (which will not process it anymore) and then, after five shifts (when in Station 10) is "unloaded" from the array (the defective product is removed from the production line, literally speaking).

[Daryl 1]

Guys, that's an excellent response, particularly good explanation from yourself Ron, but this is where it breaks down for me. I know the theory of what it's meant to do, and a typical example of applying, but unfortunately it's the actual step-by-step, doing it in practice that I need explainin. This is where Chris's link comes into it, and it seems ideal for what I need to learn. This might also be the diffrence between training with Rockwell instead of Ron's bootcamp!! If only he was in the UK! thanks... Daryl