PLC 5 Clock Setting via HMI

[tvich]

Gentlemen,

I have customer's old PLC 5/40 who's internal S register clock values fall off by a matter of minutes every month. (that issue I believe I know (DH+, and a very convoluted inefficient messaging scheme bogging down comms on the network) why and is not my purpose in this thread)

I'd like to lean on any of you if your aware of any way I can have them manually update this time (to the S register values) through their HMI? (basically performing the same function you can do online with the 'Set Date & Time' button. Can I write directly to an N register and have this one-shot into an S register? Without affecting the online process?

I THINK that when I'd do the similar function with a Logix5000, I thought it would for a short bit, actually take the processor offline and then back online again. Or maybe not this, but it definately reset some of the running process?

Thanks....

 

[Mickey]

Can I write directly to an N register and have this one-shot into an S register? Without affecting the online process?

The answer is yes you can.
The affects on your process is dependent on how you are using the clocks registers in your program. You don't have to stop the program from running (offline) to write to these registers.

 

[OkiePC]

You can (with most HMI that I have used) read/write directly to the S registers as well. As Mickey wisely pointed out, search the program to evaluate what effect your changes may have on the system.

 

[TConnolly]

I have done this on several HMIs, same way you described. I write to N registers, range check it, then write to the clock registers in the S file.

 

[bikerdude]

Hi,

I write to N registers, range check it, then write to the clock registers

A wise programmer (like Alaric) does not allow operator to load minute value of say "74" into the minute register. PLC does not like this value at all. There are operators that will put it in there just to see what happens. Maybe they are just bored? There are others that just make simple mistakes like everyone does.

BD

 

[504bloke]

Maybe they are just bored?

BD

Or those that want an extended tea break (downtime) !

I agree with alaric and bikerdude

 

[Mickey]

Hi,

A wise programmer (like Alaric) does not allow operator to load minute value of say "74" into the minute register. PLC does not like this value at all. There are operators that will put it in there just to see what happens. Maybe they are just bored? There are others that just make simple mistakes like everyone does.

BD

FYI,
Its always a good idea to range check an input from a HMI or SCADA system. But with the PLC5 if you input a value of 74 this will not fault the processor it really does not care. It will accept the value and keep on running.
What it will do is next time the second value reaches 00 the processor will add one hour to the hours register (S:21) and 15 min will show up in the min. register (S:22) if you type in the above "74".

Just though you would like to know.

Edit: I don't know what a SLC500 will do, I don't have one to play with.

 

[TConnolly]

I just tried it in a SLC 5/04 that I keep on my desk to play with.

I tried writing a 75 to S:41 by directly writing to it and programatically writing to it. In both cases the 75 was rejected and S:41 returned to its previous value. Even when the PLC is in program mode directly writing a 75 won't be accepted and the previous valid value will be restored. Same holds for S:40 and S:42, even if the clock is disabled. Only valid values are accepted.

 

[Ken Roach]

Logix 5000 Clock Update Tool

If you have a PC connected to the DH+ control network, you can get fairly accurate time updates to your controllers automatically.

If you already use a Windows Domain Controller that uses an accurate system time, stick with that. Otherwise read what the NIST has to say about the Internet time service:

http://www.tf.nist.gov/service/pdf/win2000xp.pdf

The Logix 5000 Clock Update tool is a utility to periodically update the clocks of PLCs. It works for PLC-5, SLC, and Logix family controllers. It's included in the installation of RSLogix 5000, or can be downloaded from the RA website:

http://www.software.rockwell.com/support/download/detail.cfm?ID=3680

 

[bikerdude]

HI,

Just though you would like to know.

Wow, not exaclty the results I expected. I must have ASSuMEd that there would be a crash & burn. Nice to know RA have covered the proverbial butt on this one.

BD

 

[rdrast]

HI,


Wow, not exaclty the results I expected. I must have ASSuMEd that there would be a crash & burn. Nice to know RA have covered the proverbial butt on this one.

BD

You can't go wrong by assuming crash & burn!
It is 1000 times better to take the extra time to do proper range checking before assignments, then rely on any kind of undocumented (or, in many cases) even documented features.

Some day, taking a shortcut will bite you in the nether regions if the underlying compiler or OS changes!

 

[TConnolly]

You can't go wrong by assuming crash & burn!

QFT - Especially since depending on what you are doing with the time registers, even though the PLC won't crash, your equipment or process could crash and burn before the PLC gets around to "fixing" it.

There is no substitute for good programming practices.

 

[tvich]

Hilarious. I think it's great. I ask a relatively simple question and get tons of first hand experience. "Oh..you don't want to...'or, never do..., "or, this one time..." Thanks guys. That's exactly the information I like from this site. I DON'T want to have to figure out on site what happens if an operator enters 25.

I do have a follow up per the customer request, and I've never had to do this before, any more info on automatically updated PLC times with either an HMI (RSView32) or Windows? I'd rather stick with RSView32, as if it's a coordination with Windows, that severly hinders my already slim skillset!