A little Ladder logic help

[BeepBob]

Hello,

I am trying to replicate a piece of logic on the PLC5 onto an SEL RTAC. I am using ladder on SEL and FBD. I am having issue on the ladder portion in SEL when it comes to timer timing and the SR block. I do not have an RTAC yet to test so seeing if anyone can spot logic issue.

The off logic is identical to the on logic. Screenshot added


1. I made network 1-4 , I think it is identical in functionality to the PLC5 code, except for the timer timing, I do not know why SEL does not provide a timer timing attribute. Reason I made 5 networks (rungs) is because SEL close branch...is weird

2. Network 5-6, I am trying to do the logic using an SR block, I think I can do the timer timing by accessing the T1.IN bit?

3. Any suggestion on the FBD?

 

[drbitboy]

1) the R_TRIG instructions need to use different memory structures; in the first image all of the R_TRIG instruction use the same R_TRIG1 memory structure (bit?), which I am pretty sure means only the first one will fire. Solution is either to use a different memory structure for each R_TRIG instruction, or to have just one R_TRIG instruction that writes to an intermediate bit "oneshot" that is 1 on the rising edge of the (BST XIC SAB1_TDO NXB XIC SAB2_TDO) parallel branches, and then use XiC oneshot at the front end of the four rungs that set or reset GATE_TDO_ON and GATE_TDO_OFF.

2) GATE_TDO_OFF can be removed from that logic and replaced with the equivalent of XIO GATE_TDO_ON OTE GATE_TDO_OFF.

 

[BeepBob]

I think I figured it out . Using only 3 networks. SEL makes you put in the R_trig...then it will allow you to do a parallel contact..

 

[drbitboy]

Also, XIC theTON.TT is equivalent to XIC theTON.EN XIO theTON.DN, if SEL does not have .EN then you can write a bit with a coil on a branch in parallel with the TON.

What happens if the SAB1_TDO or SAB2_TDO value returns to 0; doesn't that shorten the .TT-driven pulse?

 

[BeepBob]

Also, XIC theTON.TT is equivalent to XIC theTON.EN XIO theTON.DN, if SEL does not have .EN then you can write a bit with a coil on a branch in parallel with the TON.

What happens if the SAB1_TDO or SAB2_TDO value returns to 0; doesn't that shorten the .TT-driven pulse?

Hmmm, I am not sure. Only the FBD have the 'TP' block. In Ladder there is only the TON block.

I think what I got now looks ok. The SEL engineer says I can use an XIO on the TIMER.Q to indicate that the timer is timing.

 

[drbitboy]

3. Any suggestion on the FBD?

Yes. Rewrite the original logic without Set/Reset i.e. one coil writing to GATE_TDO_ON, and then the translation to FBD will become obvious.

 

[drbitboy]

The SEL engineer says I can use an XIO on the TIMER.Q to indicate that the timer is timing.

Only if it in series with the state of input rung of the TON.

 

[BeepBob]

Thank you for your input!

 

[drbitboy]

This reads cleaner to me, at least the last two rungs. I am pretty sure it is essentially equivalent; it does not maintain state across a PLC mode change.

It should be trivial to convert to FBD, since it is all ANDs and ORs.

 

[drbitboy]

Sorry, the second rung is wrong in that attached image. This should be correct.

SAB12R is the result of the rising edge on the on the OR (parallel XICs) of the SAB1_TDO and SAB2_TDO bits.

 

[Ken Moore]

Very familiar with the SEL RTAC's. Never saw them used for anything other than power distribution and control. The local power provider uses them at all their sub stations. Is this a gate at a power station?

 

[SCADA_Joe]

Remember to mind the time units of the timer.

I notice T74 timer is time base 0.01 and the preset is 10 so that is 0.1 seconds and the T1 is T#1S may mean it is 1 second.

 

[BeepBob]

Very familiar with the SEL RTAC's. Never saw them used for anything other than power distribution and control. The local power provider uses them at all their sub stations. Is this a gate at a power station?

Yes, we have them at our substations. But the decision was made by the top to go ahead and use them for general-purpose. Something about lengthy acquisition bureaucracy if anything else...

 

[BeepBob]

Remember to mind the time units of the timer.

I notice T74 timer is time base 0.01 and the preset is 10 so that is 0.1 seconds and the T1 is T#1S may mean it is 1 second.

Oh yes, thank you. That slipped me.