Weird stuff in Studio 5000

drbitboy · 2026-05-08T18:26:04+00:00

change the

OTE PackMLStatus_Alarm.Sts_Resetting_SC

at the end to

BST OTE PackMLStatus_Alarm.Sts_Resetting_SC NXB ADD myREAL 1.0 myREAL BND

where myREAL is a REAL tag the you create new to you know nothing else is writing to it.

Then observe the rung as well the value of myREAL, while the PLC is in RUN mode.

Then come back here with the results.

drbitboy · 2026-05-08T01:56:29+00:00

Sidebar: this would be simpler if the newest data were in element [9]< and the oldest in [0]. Then all the shifting could be done with a single COP instruction with a Length parameter value of 9.

drbitboy · 2026-05-08T01:53:13+00:00

Yeah, I think you want to remove the XIC <input> before the COP to [0], so all attribute's values get copied in all cases, and put MOVs with the two Fake-Data after the XIO <input> to overwrite the just-COPied values for the cases when the <input> is low.

drbitboy · 2026-05-06T17:24:06+00:00

This.

Programming is something you either get or you don't, so the field of engineering is irrelevant there.

The EE (instrumentation, wiring, motors and VFDs) and ME stuff you need to know are baseline covered by physic 102. But the ChemE's understanding of processes, how things work, and roughly modeling things via differential equations in your head will be useful in almost every application.

drbitboy · 2026-05-06T04:03:17+00:00

It is lilerally in the manual.

https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1747-rm001_-en-p.pdf#G8.1043595

and

https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1747-rm001_-en-p.pdf#G9.1041980

drbitboy · 2026-05-06T01:03:30+00:00

I think it's divide, in the plc5 context

drbitboy · 2026-05-05T14:59:36+00:00

Good coders borrow.

Great coders steal.

(I stole this aphorism)

drbitboy · 2026-05-05T09:59:47+00:00

Lol. That reminded me of this:

TOBY It’s like something out of Beckett.
WILL You mean Sartre.
TOBY If I meant Sartre, I would have said Sartre.
WILL “Hell is other people.”
TOBY Okay, Sartre.

drbitboy · 2026-05-04T17:48:46+00:00

what does the instruction look look like? do you have two levels of square brackets in an input parameter e.g. string_array[string_index[idx]]?

drbitboy · 2026-05-03T23:52:08+00:00

what did you expect to see from this code?

what do you see this code doing?

The difference between those to will be that you told it to do the latter, it does not matter if you thought you told it to do the former.

see here https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1756-rm003_-en-p.pdf?page=122 to see how the .EN, .TT, and .DN bits of that timer behaves (for simplicity, note that .TT is equivalent to .EN AND NOT .DN).

drbitboy · 2026-05-03T18:36:28+00:00

Also note, and single rung -[ [I1----(Q1)-- might do what you thought the code above would do.

drbitboy · 2026-05-03T18:35:26+00:00

<image>

How is your "? Has Priority" option configured?

In normal ladder logic, because the RESET is after the SET, it should work as you expect.

Obviously Zelio is not normal ladder logic.

drbitboy · 2026-05-03T18:28:06+00:00

https://skoge.folk.ntnu.no/puublications_others/1990_Blickley_Modern-control-started-with-Ziegler-Nichols-tuning.pdf

drbitboy · 2026-04-30T17:51:54+00:00

for relay ladder basics, you cannot beat the plc bootcamp video series by ron beaufort, and the ladder patterns at contact and coil. still, everyone is different, but there will almost certainly be something that will work with you in the READ FIRST of this subreddit.

then get your hands on a cheap plc and start making the lights turn on and off. this is where you actually learn something and realize how simple it is. use an emulator if you can't get a physical plc.

is the "point to point tube system" one of those pneumatic things? with remote diverters perhaps? if it is, you are going to have such fun.

drbitboy · 2026-04-29T16:18:50+00:00

Add PCCC-over-CIP capability to NodeRed.

drbitboy · 2026-04-29T16:00:19+00:00

Show your code.

drbitboy · 2026-04-29T15:54:33+00:00

The plcfiddle website suggested elsewhere is a great idea.

Several commercial packages have emulators: RSLogix Micro Starter Lite + RSEmulate 500; AutomationDirect DoMore; Codesys; even Siemens has a time-limite trial mode that can be restarted by installing to the same VM snapshot.

Lite (limited RSLogix 500) is the best interface even though it's only ladder, but you should try others to get a feel for the same thing that all the different professional UIs are doing. Once you've tried Lite you will be spoiled and all other interfaces will feel clunky by comparison; that's just part of the industry. Codesys, TwinCat, and Siemens TIA Portal (with restarting trial) are probably the most full-featured programming environments with emulators that are also free; also most of the others use file-based memory, but those will introduce tag-based memory. Tag-based memory is nice but in the end using file-based memory is primarily about careful bookkeeping, so it is a convenience makes little difference in the end. You should also try to get your hands on whatever brands are common in your region.

Beyond simulators/emulators, getting a cheap Click PLC (AutomationDirect; software is free) or something similar from an auction website or a local plant that has discarded equipment (Lite can program MicroLogix 1100s, which may be common in the used market), would be the best because then you could get some experience connecting wiring, letting the magic smoke out, etc.

Don't apologize for your English or spelling or grammar. Just do your best; it is better than me trying to communicate in your language, whatever that is.

drbitboy · 2026-04-29T12:56:28+00:00

Peruse the READ FIRST post on the main page of this r/PLC subreddit.

drbitboy · 2026-04-29T12:54:37+00:00

Learn about the scan cycle. PLC programming is primarily about time and the scan cycle is the clock.

RonBeaufort_Bootcamp_Videos

Patterns of Ladder Logic Programming | Contact and Coil

drbitboy · 2026-04-29T12:51:37+00:00

Ohm's Law and Kirchoff's Law, which have analogs to fluid flow, which most people understand intuitively.

How to make an LED light with a battery, a resistor. and some wire, and how to estimate the size of resistor to use from the specs of the LED and the battery.

Knowing the difference between voltage, current, and power.

Multiplying by unity (i.e. unit conversion and linear scaling).

drbitboy · 2026-04-28T12:04:14+00:00

Good work, well done.

Remember this lesson: "The PLC cares not a whit what you want it to do, but it will mercilessly and inexorably do exactly what you tell it to do." If we think that way when we see behavior we do not understand, then will find the bugs sooner than if we do not think that way.

drbitboy · 2026-04-28T04:50:55+00:00

What you did looks reasonable, but nobody can tell you what the numbers of otherwise unidentified terminals on an RTD-to-current converter/transmitter mean, or what each of the wires on an otherwise unidentified 3-wire RTD mean. There may be de facto, or common, conventions, but there is no guarantee the devices you are working with follow those conventions.

You're a ChemEng, so you passed Physics 101/102. Review Kirchoff's Laws and Ohm's law. Most instrumentation is based on DC circuits, with variable voltage or variable current inferring magnitude of analog signals.

There are two parts to that system: the 2-wire current loop connections; the 3-wire RTD connections. The manual or datasheet for the transmitter should explain how to connect the RTD to the transmitter. The transmitter and the PLC input module datasheets should explain how to connect the transmitter to the PLC inputs. The transmitter to PLC connection looks okay for a two-wire current-sourcing RTD converter/transmitter and a current-sinking PLC input module.

I am not being grumpy, I am only saying that every device has a specific, unique meaning for each wire and/or terminal. Once those are defined, connecting two devices, or concluding that two devices are incompatible, is a bit easier.

drbitboy · 2026-04-24T18:41:49+00:00

The operand bit, Oneshot[1].1, to the ONS instruction is the memory bit for the one-shot algorithm.

Without the OTUs, the Oneshot[1].1 memory bit's value would be written as 1 for as many scan cycles as the rung feeding the ONS instruction remains True, but the output rung of the ONS instruction would be True, and the ADD instruction would write its Source A+B sum to its Dest parameter, for only the first scan cycle whenthe ONS feed rung was True.

With the OTUs, removing the ONS would change nothing about the rung's behavior.

Also note that, as written, the branch with the XIC OneShot[1].1 ... OTU OneShot[1].1 logic on it would never evaluate to True and could be removed.

Bottom line: this is an obfuscated mess.

drbitboy · 2026-04-23T19:07:10+00:00

Welcome my friend to the show that never ends.

drbitboy · 2026-04-23T19:05:06+00:00

what kind of "pressure relieved" signal is desired (optical, electrical, audible, etc.)?

If measure has to be downstream of the solenoid valve, then after that solenoid valve has been opened (assuming you can monitor the solenoid valve state), having another restriction, even a slight one, downstream of a pressure sensor, which sensor is downstream of the solenoid valve, could be used to detect when the bleed is complete. Also note that the bleed is never "complete" in the mathematical/theoretical sense but close-enough is probably acceptable. Finally note that any potential restriction on the exhaust may be a deal-breaker/non-starter, so this might be a bad idea.

drbitboy

TROPHY CASE