Analog and digital inputs

showshocka

Member
showshocka
Join Date
Mar 2011
Location
USA
Posts
510
Hi. Why is it that I can't I find analog inputs in the project if see a "1" and I know that they're at the input card and operating. I can always find the sourcing, sinking or 110vac inputs (or I guess the digital inputs) that are at the cards when I see them..... Screenshot
 
change the radix setting (lower right corner) to "Decimal" and try again ...

the analog input channels will be addressed as

I:5.0 = channel 0
I:5.1 = channel 1
etc.

notice that these addresses use DOTS - not SLASHES ...
 
Last edited:
For viewing convenience you can also open two instances of the input file data window. Double click on the I file. Now double click on the O file. You should have two data windows. In the bottom left corner of the Output data window you will see a small field that says O0. Click the small up arrow. It will change to I1. Now click the Radix and change it to decimal. Now you can see discrete input data in the first window and analog data in the second window.
 
Screenshots....
Pic1 Open I1 and O0 data-file monitor windows
Pic2 Change the O0 window to look at I1
Pic3 Change the Radix of one of the views
Pic4 Two Views of the Input Table - Discrete and Analog

Pic1.jpg Pic2.jpg Pic3.jpg Pic4.jpg
 
in an Allen-Bradley if a 16-bit word contains ONES in ALL of its bits, the DECIMAL value that you'd have displayed would be (-1) note that's NEGATIVE 1 ...

the numbering system is called "Two's Complement Binary" ... you can read about it here:

http://www.plctalk.net/qanda/showthread.php?postid=68241#post68241

maybe you're seeing "FW" on the "Usage" feature ... if so, the F stands for "File" - the W stands for "Word" ...
 
Last edited:
Ron. I was asking that because i find that when i add up all the binary 1's in word they add up to a value such as;6009 or 5970 or 3305 etc...depending on how many binary 1's are in that word. I see the "W" representing word and I have seen that column showing "FW" also, at the time i did not pay attention to what the value of that column was but I'm guessing that it was showing 65535, maybe if the whole word line were all 1's. What's the difference in that column showing W and FW?
 
the USAGE table tells you whether or not a specific address is being used (or not) in your program file ... (basically, is this lady "spoken for" - or can I ask her to dance?) ...

NOTE THAT THERE ARE IMPORTANT EXCEPTIONS TO THE RULES WHICH FOLLOW ...

if the address has a DOT, then presumably it's NOT used - and therefore available for your programming pleasure ... (the lady isn't wearing a ring - so go ahead, ask her to dance) ... but if the address has an "X" then it IS being used ... (stay away from that particular lady) ...

BUT ... HOLD ON! ...

even if there is a DOT (not an "X") for a specific address - take a look at the end of the row and see if there's an "F" or a "W" ...

"W" stands for Walter ... so even if the address in Walter's row isn't wearing a ring – the lady is still "spoken for" if Walter's on that row ... (do NOT ask any of those ladies in Walter's row to dance – he's mean) ...

"F" stands for Frank ... so even if the address in Frank's row isn't wearing a ring – the lady is still "spoken for" if Frank's on that row ... (do NOT ask any of those ladies in Frank's row to dance – he's even meaner than Walter) ...

SO ...

whenever an address is used by something like an MOV (Move) instruction, the individual bits do NOT show up as X's (with rings) – but the "W" means that those bits are being controlled at the WORD level ... you can't just use them in your program without first understanding how the Word-address is using them ...

whenever an address is used by something like a COP (Copy) instruction, the individual bits do NOT show up as X's (with rings) – but the "F" means that those bits are being controlled at the FILE level ... you can't just use them in your program without first understanding how the File-address is using them ...

hope that helps – out of typing time for awhile ...
 
Last edited:
That puts it in complete perspective Ron! BIG thanks. You wouldn't happen to have an analogy like that for "PID" control would you? Also what are other Lyman's terms i can substitute for the P the I and the D?
 
be careful what you ask for ...

click the link below my signature ... go to the "Sample Lessons" page ... there are links there for basic PID stuff - and more ...

tip: if you've going to watch the YouTube videos, be sure to watch them all IN NUMBER ORDER! ... skipping around is not advised ...
 
Ron Beaufort said:
the USAGE table tells you whether or not a specific address is being used (or not) in your program file ... (basically, is this lady "spoken for" - or can I ask her to dance?) ...

NOTE THAT THERE ARE IMPORTANT EXCEPTIONS TO THE RULES WHICH FOLLOW ...

if the address has a DOT, then presumably it's NOT used - and therefore available for your programming pleasure ... (the lady isn't wearing a ring - so go ahead, ask her to dance) ... but if the address has an "X" then it IS being used ... (stay away from that particular lady) ...

BUT ... HOLD ON! ...

even if there is a DOT (not an "X") for a specific address - take a look at the end of the row and see if there's an "F" or a "W" ...

"W" stands for Walter ... so even if the address in Walter's row isn't wearing a ring – the lady is still "spoken for" if Walter's on that row ... (do NOT ask any of those ladies in Walter's row to dance – he's mean) ...

"F" stands for Frank ... so even if the address in Frank's row isn't wearing a ring – the lady is still "spoken for" if Frank's on that row ... (do NOT ask any of those ladies in Frank's row to dance – he's even meaner than Walter) ...

SO ...

whenever an address is used by something like an MOV (Move) instruction, the individual bits do NOT show up as X's (with rings) – but the "W" means that those bits are being controlled at the WORD level ... you can't just use them in your program without first understanding how the Word-address is using them ...

whenever an address is used by something like a COP (Copy) instruction, the individual bits do NOT show up as X's (with rings) – but the "F" means that those bits are being controlled at the FILE level ... you can't just use them in your program without first understanding how the File-address is using them ...

hope that helps – out of typing time for awhile ...
Click to expand...

AND, don't forget about words and that may be written from an HMI or another PLC. More than once I've used a single unused integer bit only to get unexpected results...
 
from rguimond:

AND, don't forget about words and that may be written from an HMI or another PLC.
Click to expand...
absolutely – and that's one of the exceptions that I had in mind when I mentioned this:

NOTE THAT THERE ARE IMPORTANT EXCEPTIONS TO THE RULES WHICH FOLLOW ...
Click to expand...
another potential "gotcha" are Indirect Addresses which never show up in the Usage feature ...

and another would be Indexed Addresses – if your program manipulates the S:24 "Index Register" as an offset ...

as always, so much to learn – so little time ...
 

Similar Topics

O
PLC Digital inputs & Analog Inputs Signal
Hello, I was wondering if you guys could help explain to me how the wiring and signal on Digital and Analog inputs/outputs run from the PLC to the...
Replies
2
Views
2,669
Ones_Zeros
O
M
Koyo Do-More PLC Digital/Analog Inputs
Hello all, I am a recent graduate at my first job tasked with a PLC project. I need to control a linear actuator given feedback from several...
Replies
5
Views
2,150
bernie_carlton
bernie_carlton
C
Using analog inputs for digital signals
Dear, I was looking at tender documents / drawings and this have indicated that they are using analog input for digital signals. I was wondering...
Replies
2
Views
1,834
kvogel
K
C
Analog input to digital output using structured text or one of IEC 61131-3 standard
Hello, I have a small programming task that I need help solving. I have to: * Create an analog input (4-20v)and a digital output * The analog...
2 3 4
Replies
45
Views
25,073
parky
P
D
Digital to Analog I/O
I am attempting to interface a Mistras acoustic sensor to a AB Micro820. The problem I have is the sensor logic is 3.3VDC and Micro820 is 24VDC...
Replies
10
Views
2,396
dlweber
D
Back
Top Bottom