Questions?!?

[just_lionel]

Hello Guys!

I have been busy, practicing my programming skills in RSLogix 500 (I've also done a little in ControlLogix, but mainly have focused on RSLogix 5 and 500)

The question I have right now (there will be more to follow, I promise that!) is what actually is the S1:15 used for? I know its used for First Pass. Does it reset timers and counters? What is it use in programming?

Thanks for all your help!

Just_Lionel

 

[Thomas Sullens]

alot of info

Go to search and type S:1/15 there is alot on this.

 

[just_lionel]

I knew there was but for some reason couldn't get it pulled up. Found what I was looking for now. Thanks!

 

[Steve Bailey]

It is used to do whatever the programmer needs it to do. Yes, you can use it to reset timers and counters if it makes sense to have timers and counters reset whenever the PLC first starts up.

It can be used to write default values into data registers. It can be used to clear faults. It can be used to restore the PLC program to a known condition. The possibilities are limited only by the constraints of the application and the limits of your imagination.

 

[Eric Nelson]

The "First Pass" or "First Scan" bit is used for anything you want to happen ONLY ONCE, and ONLY AT POWERUP (or change to run). This could be, as you suggested, used for resetting counters, etc... :nodi:

I myself use it to do any 'prep work' at startup. I usually have a 'startup' subroutine that is triggered by the 'first pass' bit. I'll put stuff like COM port settings in there. Things you only need to do once. In AB PLCs, I use FLL instructions to reset stuf I don't want retained through a power cycle, such as sequencer bits.

Note, you can also use XIO S:1/15 to IGNORE the first pass.



-Eric

 

[just_lionel]

It is used to do whatever the programmer needs it to do. Yes, you can use it to reset timers and counters if it makes sense to have timers and counters reset whenever the PLC first starts up.

It can be used to write default values into data registers. It can be used to clear faults. It can be used to restore the PLC program to a known condition. The possibilities are limited only by the constraints of the application and the limits of your imagination.

Ok. I think I understand it now. Now for your avatar. Which two are they?

 

[just_lionel]

The "First Pass" or "First Scan" bit is used for anything you want to happen ONLY ONCE, and ONLY AT POWERUP (or change to run). This could be, as you suggested, used for resetting counters, etc... :nodi:

I myself use it to do any 'prep work' at startup. I usually have a 'startup' subroutine that is triggered by the 'first pass' bit. I'll put stuff like COM port settings in there. Things you only need to do once. In AB PLCs, I use FLL instructions to reset stuf I don't want retained through a power cycle, such as sequencer bits.

Note, you can also use XIO S:1/15 to IGNORE the first pass.



-Eric

Okay, so more or less I can set it up for what I want it to do? I am writing a program that controls a conveyor system that brings meat up two seperate belts onto one big belt. If the E-Stop is triggered, I have it setup to kill power to everything (including the PLC).

Once power is restored, I want to reset all outputs, and reset all timers to zero. So with the First Scan I can do this correct?

 

[jstolaruk]

If the E-Stop is triggered, I have it setup to kill power to everything (including the PLC).

O/T, Why not just kill power to motion/non-safe outputs using a safety relay deactivated by the E-stops?

 

[Eric Nelson]

Once power is restored, I want to reset all outputs, and reset all timers to zero. So with the First Scan I can do this correct?

Yes.

I personally don't like (read: HATE) killing power to the PLC on E-Stop. Kill power to the ouputs, but leave the PLC on. Just 'inform' the PLC that the E-Stop is pressed (better yet, NOT pressed) via an input. Then, do whatever you need to in logic when this occurs.



-Eric

 

[just_lionel]

Yes.

I personally don't like (read: HATE) killing power to the PLC on E-Stop. Kill power to the ouputs, but leave the PLC on. Just 'inform' the PLC that the E-Stop is pressed (better yet, NOT pressed) via an input. Then, do whatever you need to in logic when this occurs.

Okay. That makes sense. For some reason, I thought most people killed power to the entire PLC when the E-Stop was pressed. I thought this was strange but I thought I was just crazy.

In this case the outputs I have are 3 480V motors. So when the E-Stop is pressed, kill power to these motors. In the logic, reset the outputs (Timers and Binary Bits). (Forgive me, I am thinking 'outloud' helps me a bit)

This isn't a major program, ten rungs, few outputs, inputs are buttons and photo eyes. I am having a few problems, but I think I have most of them worked out, trying out a few different things. Once I get it like I want it (or can't get pass a problem) I will post it so everyone can give me constructive criticism.

I do thank everyone for their help here. I've learned quite a bit. I might not have posted alot, but alot of people have covered what questions I have. No reason to repost them!

 

[Ron Beaufort]

are we making this harder than it needs to be? ...

Once power is restored, I want to reset all outputs, and reset all timers to zero. So with the First Scan I can do this correct?

in simple terms: yes, the First Scan bit can help you do that ...



but going further ... IF (big IF) your “outputs” are all held on by “seal-in” rung constructions (as opposed to “latched/unlatched” rung constructions) and IF (another big IF) all of your timers are TON (Timer On Delay) type timers, then you really don’t have to do ANYTHING to accomplish what you asked for ...



specifically, with an Allen-Bradley processor, a “seal-in” rung will automatically “turn off” whenever the processor first goes into the Run mode ...



and ...



with an Allen-Bradley processor, a TON timer will automatically “reset” whenever the processor first goes into the Run mode ...



I think if you’ll experiment a little bit, you’ll probably save yourself quite a lot of extra programming work ...



do we need to talk about the “retentive” properties of Latches? ... and RTO timers? ...

 

[just_lionel]

Yes, I have a bad habit of making things harder then they need to be.

 

[Ron Beaufort]

No reason to repost them!

yep ... but that's never stopped anybody else ... but we really do appreciate your consideration ...

 

[Ron Beaufort]

I just noticed that you mentioned "counters" in your original post ... now THOSE are likely candidates for the judicious use of an S:1/15 "RES" rung ...

and going even further ... I wouldn't disagree with anyone who makes the following argument:

"I always reset all of my outputs and all of my timers with S:1/15 ... even though I realize that I don't really need to do it ... because ... it helps the maintenance technicians understand that each and every time the machine starts up, these items will definitely start out at a known and predictable state ... "

I'd say that's a perfectly valid argument ...

 

[Steve Bailey]

Now for your avatar. Which two are they?

Whichever two you want, but only two on any given project.

Good and fast won't be cheap. That's because I've got to drop everything else I might be doing to get your job done fast and still do it well.

Good and cheap won't be fast. You want good work at a discount price? OK, but when somebody else comes along willing to pay full price, whose job am I going to let slide?

Fast and cheap won't be good. Needs no elaboration.