New to plctalk.net

Welcome to the site - no problems we will happily mislead you.

at the end of the day any understanding of logical control will help you have a look at the download section of this site.
you need to prepare yourself for the inevitable change over of PLC's from old to new.
there are heaps of student questions/posts on this site.
CONVEYOR / TRAFFIC LIGHT / ELEVATOR / LIFT controls
Also FLIP FLOP (latching button)
I like to teach relay logic to convert to PLC
- three relays one light one PB
- two way light control
- star delta start
etc
All are well known and a good start

thanks for the reply, i'm finding lots of useful information on this site! its awesome

Hey Brian. Welcome to the PLC world. I have been in the field for a few years now and somedays I still feel like a begginer. There is something to be learned everyday. I have found this site very helpful. Also I resieved training from a company based in Ontario. They are called Automation Training. Great bunch of guys. I recommend you take PLC 500 introduction course followed by the advanced course. This will teach you foundamentals and more complicated practices. I also took the Control Logix course they offer. You have a plant full of old equipment so learning the new technology is esential to getting them out of the stone ages.

good to see another Canadian on line. We are few and far between.

:beer:mate we even get KIWIS here:beer:

actually I'm registered to start the allen Bradley plc 5 fundamentals on july 15 with automation training, i'm doing the online course which I heard was pretty good. I more or less need to learn the analog aspect of the PLC world. I've worked with lots of discrete and understand its principles pretty clear. But seeing as how we have tonnes of process control I really need to get up to par on the analog aspect of PLC's and how it all works, would make my job a lot less confusing!

Pay a lot of attention to Scaling. Older PLC's had different methods of scaling in the modules (raw, PID, engineering, others) and others are done in ladder commands. Some dont make sense until you have one already in place and have to figure them out backwards.

Welcome to the frey, its a lot of fun !

TheWaterboy said:

Pay a lot of attention to Scaling. Older PLC's had different methods of scaling in the modules (raw, PID, engineering, others) and others are done in ladder commands. Some dont make sense until you have one already in place and have to figure them out backwards.

Welcome to the frey, its a lot of fun !

Click to expand...

Plus even modules in the same series have different scaling depending on the module itself. For example a 4-20mA Input on a 1762-IF2OF2 has a raw data format of 6240-31200, but on the 1762-IF4 its 6241-31206. On the 1762-OF4 the output range is 3120-15603 for 4-20mA.

not entirely sure what scaling is, sounds like alien language right now!

brstilson has reinforced what I meant
.
Scaling is when you have a signal input, be it voltage, 4-20ma current loop or whatever else, and "scaling" or converting that value into a range you want to work with.
For example a valve that has a position feedback will have a 4ma signal indicating closed and a 20ma signal indicating open.

Scaling means taking that range of 4ma to 20ma and converting it into the integers 0 through 100 so you can display it as percent.

in the case of the IF4 module, instead of the numbers 0-100, you see 0ma = 6241 and 20ma = 31206. Thats a little harder to work with and that has to be "Scaled" back to 0-100 to be a useful display value.

Hope that helps a little.

Sorry Waterboy - slight mistake in your post, (0ma = 6241) should read (4ma = 6241)
Brian - simple Analogue -

think of a mug of coffee when it is empty and when it is full 0 ~ 100%
Half Full = 50%
1/4 Full = 25%

we have sensing devices that can detect the level of this cup
they give an output of either voltage or current
The sensor ranges on the market are 0 ~ 10V +/-10V also 5V
and 0~20mA or 4~20mA

when we talk scaling we say that empty = 0% or 0 height for example
with a 4 ~ 20 mA sensor 0 = 4 mA
so a Full Cup is %100 or 3"
this would be 20 mA
using an SCP instruction - Which you will learn (Scale with Parameters)
you set this up in the PLC.

THEWATERBOY and BRSTILSEN has highlighted the problem with Analogue Input cards.
They have a 'BIT' digital accuracy - there are a different number of BITS depending on the Manufacturer or Cost of the device - Also what is needed . (who cares if the coffee cup is 49.99995% full)
the AB cards are selectable for either Current or Voltage
The range is also settable.
BUT with a 4~20mA sensor the AB card range is 0 ~ 20mA
AS a result the actual "ZERO" value will not show as 0 - IT WILL DEFAULT TO NEGATIVE (32000 approx)
THIS IS WHERE AB IS FUN
KEEP THIS POST CLOSE TO YOU
This information is about 10 ~ 15 pages further in the manual than where it should be - BUT IT IS CRUCIAL
the info posted by BRSTILSEN is the most useful you will find

iant said:

Sorry Waterboy - slight mistake in your post, (0ma = 6241) should read (4ma = 6241)

Click to expand...

:facepalm:

See how confusing it gets!

You have come to the right place.

Key things:

RSLogix5 and 500 have key differences. Critical among them:

1) Addressing. Get used to octal. Its easy and only really applies to I/O in the PLC5. Getting used to 1/2 slot, single slot, and two slot addressing isn't simple, but once you know how to apply some basic rules (which I always have to look up) it is not all that complicated until you have to figure out some undocumented system with no back up files.

2)I/O documentation. While ONLINE in RUN mode, if you drill into the nooks and crannies, you might find completely inaccurate information with RSLogix5 for the I/O layout while this is impossible with a SLC500. I like to get the latest and greatest commented code and make sure that the channel configurations and I/O layout stored in the RSLogix5 windows file actually matches what is going on inside and along the blue hoses of of the 1785 series processor. I am a big fan of the PLC-5. Once you have the documentation done and stored in the RSLogix5 file, there are shortcuts to getting the analog data which is actually running in each smart module (analog and some others).

3) The PLC5 memory layout is fixed, you tell it which channels to scan and which addresses and it does not care what is out there. Some foolhardy and lazy folks even hot swap the cards without problems , while the SLC will fault immediately if any card goes missing or is wrong.

4) The PID instruction has an ideal base rung structure that is totally different between them.

5) Communications. The PLC-5 isn't quite as powerful as a Logix 5000 controller but is ten times or more better and communications than the single CPU SLC. The PLC-5 has been called by its designers a multi channel "block transfer machine". And the block transfer instructions in all their applications are very different between the slot based SLC scanner and the multi-channel PLC-5.

I am sure others can add to this short list...