Lost Bits?

Hello i am new to the board and kinda new to the PLC field.

Anyway i have an ongoing debate at work about bits getting lost. I have seen for what ever reason bits sometimes getting sent and never recieved. Can anyone explain in terms that our production supervisors who know nothing about PLC's can understand) how this can happen(Besides programming errors)

How i explain it is its like the old TV's that used bunny ears. The signal from the tv station is sent loud and clear because of interferance (electrical or material) that signal is broken up sometimes even lost.

our plant engineer does not agree with me. What does everyone else think? Any input would be appreciated!!

Bits getting lost?
And where are they sent from and to?

If you are talking about communications (serial, Modbus, Ethernet, Profibus, etc.), then unless using a completely 'dumb' protocol, data should never be actually 'lost' unless there is a cabling problem.

That doesn't mean that every message from a sender to a receiver will make it intact, they might be corrupted by noise, or power glitches, or collision's, but if so, the sender will try to re-send the data, or the receiver will re-request it, or it will be sent at the next scheduled interval, depending on the actual protocol.

Bit's do not very often leak out of a wire and go off exploring on their own.

I think "programming errors" or sensor setup covers it if you're talking about PLCs. RD is right (and funny!) bits are not often found wandering around out on the plant floor. You may be missing events due to scan time or sensor settings or simply incomplete logic, especially if the machine or process was changed. But no, the bits didn't get lost; they simply were not processed, or were not processed as expected. If you are seeing machine or process downtime, it's correctable.

Someone has been watching too much Tron

Losing a bit would imply that time is lost too. Bits sent over a serial port / Ethernet affect the signal on the wire for a period of time ( bit time ). How does one lose a bit without losing the time it exists on the wire? Rdrast explained well what can happen during this bit time.

TVs back then were analog. Analog signals also exist in time and have a analog value for every nano second. The problem you describe occurs when the TV cannot detect the sync levels between the frames. It doesn't mean that the time the sync levels were not there and therefore lost.

If anyone needs any, I found 3 bits the other day! They aren't mine, but they followed me back to my desk. I've been trying not to feed them, but they are so cute!!!!!

brucechase said:

If anyone needs any, I found 3 bits the other day! They aren't mine, but they followed me back to my desk. I've been trying not to feed them, but they are so cute!!!!!

Click to expand...

I would take one of the bits, but I'm worried that it might multiply with an integer I had laying around. That integer is some hot number!

2 bits will still get ya a soda, save the other one till ya find another.

brucechase said:

I found 3 bits the other day

Click to expand...

Have you checked what state they were in? (And don't give me this 'Georgia' s**t )

And what species? Were they common bits, drill bits, or the rarer parity bits?

Ken

rsdoran said:

2 bits will still get ya a soda, save the other one till ya find another.

Click to expand...

If you can still buy a soda for 2 bits, I wanna come live where you do. Costs at least a word here.

As you've seen, bigr, more details about the sort of occurrences you are observing would be necessary for serious discussion.

"Lost bits" or "missing bits" sounds like you're chasing a missed-events situation involving an intermittent sensor or an I/O update speed or technique problem.

So much of industrial controls is digital, with built-in error checking and detection, it's hard to have a signal simply disappear into the ether without the failure being detected by the sender.

I'll trade you more speculation for more data.

Lost bits do not eat much

Lost bits do not eat much, just a few nibbles!!

Here's a recent example of some lost bits:

010101011010101101010000010100010010000101010101
001010110101011010100000101000100100001010101010
101011010101101010000010100010010000101010101010
010101011010101101 10000010100010010000101010101
010101101010000010100010010000101010101010101011
010000010100010010000101010101000000000000000000
010101011010101101010000010100010010000101010101
001010110101011010100000101000100100001010101010
101011010101101010000010100010010000101010101010
010101011010101101010000010100010010000101010101
010101101010000010100010010000101010101010101011
010000010100010010000101010101000000000000000000
010101011010101101010000010100010010000101010101
001010110101011010100000101000100100001010101010
101011010101101010000010100010010000101010101010
010101011010101101010000010100010010000101010101
010101101010000010100010010000101010101010101011
010000010100010010 00101010101000000000000000000
010101011010101101010000010100010010000101010101
001010110101011010100000101000100100001010101010
101011010101101010000010100010010000101010101010
010101011010101101010000010100010010000101010101
010101101010000010100010010000101010101010101011
010000010100010010000101010101000000000000000000
010101011010101101010000010100010010000101010101
001010110101011010100000101000100100001010101010
101011010101101010000010100010010000101010101010
010101011010101101010000010100010010000101010101
010101101010000010100010010000 01010101010101011
010000010100010010000101010101000000000000000000
010101011010101101010000010100010010000101010101
001010110101011010100000101000100100001010101010
101011010101101010000010100010010000101010101010
010101011010101101010000010100010010000101010101
010101101010000010100010010000101010101010101011
010000010100010010000101010101000000000000000000

Remember too many bits and they could well BYTE you if you turn your back on em!

I found it!!!!

Here it is 0.

I have all my bits, just missing some pieces.