Another Allan-Bradley Newbie

[fasacrifice]

Hi All,

I've been using GE and Siemens for a long time and just switched to Allan-Bradley because of one of our customers requirements.

Unfortunately not happy at all so far. When i was switch from GE to Siemens, it was a great experience.

The first thing I don't understand that all the memory area is retentive in AB and there is no way to change it, right?

Isn't that dangerous and also lots programming and caution required? I have to take care of every single bit to see if it's gonna cause any problem or not when I start up first time.

Is there any way to clear all the memory at the first cycle?

Am I wrong so far or missing anything?

 

[rdrast]

Yes, all memory is retentive.
You can explicitly clear whatever you like, but even on the other platforms, if you wanted something in a defined state on power up, it is a good idea to do it explicitly.

Pre-scan on AB processors will ensure that all OTE bits are reset to false before the first actual program scan, only OTL/OTU are ignored during the pre-scan.

There is "Lots of danger and caution required" for any system capable of controlling lethal equipment. What is your actual issue?

 

[fasacrifice]

Yes, all memory is retentive.
You can explicitly clear whatever you like, but even on the other platforms, if you wanted something in a defined state on power up, it is a good idea to do it explicitly.

Pre-scan on AB processors will ensure that all OTE bits are reset to false before the first actual program scan, only OTL/OTU are ignored during the pre-scan.

There is "Lots of danger and caution required" for any system capable of controlling lethal equipment. What is your actual issue?

Too bad I am not wrong so far. I have thousands of tags. How am I gonna take care of them all? I just want a clean start up. I don't want anything to move or do anything without my command.

Is that a nice feature on AB or what? What do you guys think? Can you give me an example that keeping all the data retentive is good?

 

[rdrast]

Beats having to have an operator enter four or five hundred settings after a power failure.
Use the system first scan bit, and make it behave like your GE, Wiping out all memory if that makes you feel better.

Create an Initialize routine to be executed only when you want to completely zero out all data.

 

[fasacrifice]

Beats having to have an operator enter four or five hundred settings after a power failure.
Use the system first scan bit, and make it behave like your GE, Wiping out all memory if that makes you feel better.

Create an Initialize routine to be executed only when you want to completely zero out all data.

Yeah but you are talking about settings. I use retentive memory for all settings anyways on other platforms. What I'm worrying about is the actual outputs and things do the real stuff other than settings.

Is there an easy way to wipe out all memory at first scan? or have to do it one by one?

 

[Mickey]

Is there an easy way to wipe out all memory at first scan? or have to do it one by one?

You don't have to do it bit by bit you can do it on a word level. Just move zero to the 16 bit word. Or "Clear" the word.

 

[fasacrifice]

You don't have to do it bit by bit you can do it on a word level. Just move zero to the 16 bit word. Or "Clear" the word.

Ok. Thanks a lot.

I don't really wanna start a big discussion I just only wanna understand the real concept behind it.

Not all my data in word format. So many bits too. In this case I have to clear bit by bit or create mapping those bits to words then clean. It's still lots of work.

I just wanna hear the real life experiences that how people deal with these retentive bits.

 

[jraef]

Allan is a first name, Allen is a last name.

Allen-Bradley is named after the founders; Dr. Stanton Allen, a physician and Lynde Bradley, a 26 year old engineer patient of his who convinced him to invest $1,000 to start a company making carbon pile resistors at the turn of the previous century.

Every time you spell either name wrong, your price goes up 1%...

 

[jstolaruk]

As noted, the default for coils, be it internal tags or real I/O, is false unless OTL is used.

Something doesn't sound right here. Member tags in DBs and M bits and words are retained in Siemens, its basically the same in A-B. Can you give a exact example of your concern?

 

[fasacrifice]

As noted, the default for coils, be it internal tags or real I/O, is false unless OTL is used.

Something doesn't sound right here. Member tags in DBs and M bits and words are retained in Siemens, its basically the same in A-B. Can you give a exact example of your concern?

DBs are retentive in Siemens. That’s where I use them when I need a retentive memory like settings. Any kind of Ms are not retentive unless you define them inside the retentive M area which can be set manually. I usually set it to zero so none of the Ms are retentive.


The problem is OTLs. It’s same as SET coil in Siemens, right? I used them a lot and want them to be zero when I start up.

 

[jstolaruk]

Ah, that's why. Then, as noted earlier, make a routine that clears all of those latches on the first scan.

Most programmers I work with keep latch instructions (and one-shots) to a minimum and never are they used on real I/O outputs. We latch tags to survive a power up-down situation and if they don't need to survive that event we don't use them.

 

[fasacrifice]

Ah, that's why. Then, as noted earlier, make a routine that clears all of those latches on the first scan.

Most programmers I work with keep latch instructions (and one-shots) to a minimum and never are they used on real I/O outputs. We latch tags to survive a power up-down situation and if they don't need to survive that event we don't use them.

OK Thanks good to know. When you said "Most programmers I work with" you mean AB programmers or any kind of PLC?

I've found that SET instructions and one-shots are very useful. Do you think it's a wrong programming strategy or I've just never used AB before so they were useful to me?

 

[jstolaruk]

OK Thanks good to know. When you said "Most programmers I work with" you mean AB programmers or any kind of PLC?

I've found that SET instructions and one-shots are very useful. Do you think it's a wrong programming strategy or I've just never used AB before so they were useful to me?

Any.

The reason is that debugging a program with multiple SETs and RESETS on tags is very difficult, especially to a maintenance electrician. They are used to seeing simple rungs where one and only one output instruction is used. They can review the conditions that turn it on/off easily.

If the output needs to remain on when a condition that turned it on is removed (like a PB start on a motor) then the output should be sealed with itself (or the contactor monitoring input if its available). The stop PB would break the seal.

 

[fasacrifice]

Any.

The reason is that debugging a program with multiple SETs and RESETS on tags is very difficult, especially to a maintenance electrician. They are used to seeing simple rungs where one and only one output instruction is used. They can review the conditions that turn it on/off easily.

If the output needs to remain on when a condition that turned it on is removed (like a PB start on a motor) then the output should be sealed with itself (or the contactor monitoring input if its available). The stop PB would break the seal.

So It seems that I have to change my programming habits with AB. No choice anyways with retentive memory.

I have another question about programming languages. In Siemens, I was using let’s say %50 of the time ladder and rest Structured Text (ST) because I found that doing math calculations and step operations are much easier with ST.

In AB, it seems math calculations are much easier with Ladder. You can do so many calculations in one block.

So What do you guys usually use for what reason?

 

[jstolaruk]

I would change your habits with Siemens too, your electrician will thank you.

If its just a couple, I use ladder because I can edit online.

If its a lot of initializing on the first scan, then ST but remember it can't be edited online.