What does "B3:0" mean in ladder

Good day. Very new at AB PLC and trying to learn, using AB provided materials. I'm familiar with Fanuc, Hitachi, and Siemens PLC's, not AB's. I have a hoist that wont raise unless the bypass key switch is turned-on (which bypasses OT switches). When I look on the ladder it shows that B3:0 (looks like NO contact) must close for it to work. Any help anyone could be would be greatly appreciated.

B3:0 is only defined to the word level. To be used in a boolean instruction it needs to be defined to the bit level. If you look below and on the right side of the contact there should be another number, between 0 and 15. That is the bit address.

B addresses are general purpose memory locations that are usually used for boolean operations. They don't have a specifically defined purpose. As MasterBlaster said there is probably an output instruction somewhere in the program that controls the state of this bit. Find that and you find what sets the bit.

Keith

Welcome to the forum

B3:0 is a Bit file 3 word 0 that has / 16 bits
I feel you will get a better understanding of how these work if you work through Ron Beauforts U Tube videos.
link below
http://www.ronbeaufort.com/sample_lessons.htm

Ok, so it's an internal I/O (like the F or G in a Fanuc)?

Right click on the address. Select Find All. A window will pop up where you can find the output instruction that sets bit B3:0/?. Click on it and the program will take you to that rung.

Also right click in any blank space on your ladder display to pull up the display properties. Select address dispaly, and select single line display for bit instruction instead of split line - that should help you see that the address isn't B3:0 but it is B3:0/X where x is a bit between 0 and 15 in Boolean file 3, word 0.

You can find the AB manuals for whatever PLC it is you are using in the literature library on AB's website. I strongly suggest you get them if you are going to be mucking about in one, especially get the addressing manual and the instruction set reference manual so that you can understand AB's memory file structure. AB does not used fixed memory locations, you can expand or shrink your data space as needed and add extra files of any data type supported by the PLC.

Ok, so it's an internal I/O (like the F or G in a Fanuc)?

Click to expand...

Yes, but pay attention to Keith's comment. B3:0 is an incomplete address when you search for the coil (OTE) instruction. The complete address is B3:0/xx where xx is the bit number between 0 and 15.

A "B" register is just internal bits...

B3 indicates which file -- you can also define a B10 or a B42 file (for example). They're just words of 16 bits each.

B3:0 indicates the first word in the file. B3:1, the second; B3:2 the third, etc...

B3:0/0 is the first bit in the first word of the B3 Binary file...
B10:4/6 is the seventh bit in the fifth word of the B10 Binary file...
etc.

It's possible for an HMI to be writing (probably at an operator button press) to B3:0/xx. So you may not see it as an output.

Hello,

And to add that in some AB processors B3/1234 is also allowed as a bit reference.

Good luck,

Mark
http://www.peakhmi.com/

Thank you all so much. Was a discrete that wired with the wrong logic (compared with PLC instruction). Problem resolved. It is amazing how quickly you folks came to my aid. Thank you