Hey guys. Case erector, Compact GuardLogix 5069-L306ERS2, pusher on a Kinetix 5300 with STO from the safety outputs. Light curtain on the infeed is a 30 mm resolution unit, mounted 200 mm from the pusher, OSSDs into a 5069-IB8S.
The auditor flagged the curtain distance. He wants the ISO 13855 calculation in the file and says 200 mm is not it. Nothing changed since commissioning, the machine has run two years like this.
All I have is a trend from the drive, curtain output to zero speed, about 300 ms. I tried the curtain vendor and they say buy the 14 mm version and it will be fine.
I would rather not move the curtain, the guarding is welded around it. How is the distance actually calculated, and does the finer curtain fix it, or any pointers?
300 ms from what to what, exactly, and measured with what? A drive trend starts when the drive hears about it. The curtain heard about it earlier.
Trend starts at the STO input dropping on the drive and ends at zero speed. So it misses the curtain response, the IB8S, the safety task and the output. Curtain datasheet says something like 15 ms response, not sure without checking properly. Safety task 10 ms, RPI 10 ms.
Then T is not 300. Curtain, input, task, output, drive, mechanics, all of it, worst case. Measure it with a stop-time meter on the curtain, not with a trend. Every auditor I have met asks for the meter reading first and the drive trend never.
While you wait for a meter, the arithmetic. ISO 13855: S = K x T + C. For a curtain up to 40 mm resolution you start with K 2000 mm/s, and if that comes out over 500 mm you may redo it with K 1600, minimum 500. C is 8 x (d minus 14), so 128 mm for your 30 mm curtain, 0 for a 14 mm one.
With T at 0.3 s: 1600 x 0.3 is 480, plus 128, call it 610 mm. With the 14 mm curtain it is 480, and the standard does not let you go under 500 with the 1600 figure, as I read it. The vendor's curtain buys you about 100 mm and you are still three times your 200. And your T is bigger than 0.3.
Borrowed a stop-time meter from the sister plant. Actuating the curtain with the meter's test rod, worst of ten: 340 ms to the pusher standing still. So the trend was optimistic by 40 ms.
Then 1600 x 0.34 is 544, plus 128 for the 30 mm, about 670 mm before anyone argues. Move the curtain, or cut the stop time hard and recalculate. Faster safety task helps T by a few ms, not by 300. Longer version of the formula and the PL side here: https://plctr.com/introduction-to-functional-safety-in-plc-programming/
Curtain is moving. Fabricators are cutting the guarding back and remounting at 700 mm, the pusher decel is also being looked at by our motion person to bring T down, but the distance is what we are certifying against. Auditor accepted the calculation with the 340 ms meter reading and the 700 mm.
What it came down to is that the curtain was put where it fitted at commissioning and the 13855 sum was never done, and the 300 ms I had in my head was a drive trend, not a stop time. The meter reading and the 700 mm are what went in the file.
I still do not know who settled on 200 mm two years ago, and nothing in the handover pack says. Thanks mattr and boris_h.
Meter reading in the file, not a drive trend.