Why does Q = output?

[Kevin_OTI]

Hello, Some co-workers and I have recently started learning Siemens after spending our professional lives in Allen-Bradly world. One thing we cannot wrap our heads around is that in Siemens, the short hand for output is Q. In AB world your inputs and outputs are labeled I and O respectively, but in Siemens world inputs and outputs are I and Q. We asked several more knowledgeable co-workers about this and they had no clue (I guess it never occurred to them). In what language does Output begin with a Q? Was it just a random decision when Siemens was first in development? Thanks.

[Crossbow]

Q doesn't look like a zero.

[Mark-]

Hello, Concur with Q does not look like zero. OP. Siemens is not the only entity using Q in place of 'O'. In electronics, Q is very common.

[Kevin_OTI]

Well an I looks like a 1. That does not sound like a reasonable explanation.

[Kevin_OTI]

After doing some more research I discovered that as well. I'm still very curious as to the explanation behind Q being used to symbolize Output. As I stated above, an I looks like a 1 so why do they still use I for input? Edited December 14, 2011 by Kevin_OTI

[Rodney]

Not to try and confuse the question however the I and Q were for the english speaking countries.. The german is E for inputs and A for outputs. Rod Edited December 15, 2011 by Rodney

[Mark-]

Hi, While I (uppercase I) and 1 look alike it is closer to l (lower case L) on older systems. The font you selected had the horizontal bar at the top and the bottom. The font I am using now does not contain the bars on the uppercase I. Take a look back when all font characters had the same width, 0 and O were identical width. You might see 0 with a slash through it to distinguish the two. Today you still might see the slash in a zero. Also remember, paper and pencil/pen were first. A guy writing 0 or O might not make sure the O was wider. And then when copied and reduced it was undistinguishable. That little tail on the Q was all that was needed.

[Crossbow]

Many PLC vendors don't differentiate input and output with I and O or I and Q. The IEC Standard uses I and Q. Mitsubishi uses X for input and Y for output, which is far more obvious. Omron and the old Modicons just assigns numbers, not letter required. Telemecanique products used I and Q since they were European, and that's where the IEC spec really took hold first. So which did come first, the chicken or the egg??

[Rodney]

this is the Mitsubishi IEC programming software. where it is progammed as in a tag form but the Mitsubishi still use the X and the Y which is the software downloaded to the P.L.C. But the IEC as Crossbow mentioned has the X and Q

[VoltSmith]

Transistors are denoted by Q in electronics. I always thought that was the source of Qs in PLC domain.

[DanW]

I thought Q meant Q for Quelle, meaning "source", as in, outputs source current or voltage. Siemens' technical dictionary, Fachwörterbuch Energie- und Automatisierungstechnik, in the German English volume has Quelle f(Transistor: "Source")/ source n Dan

[Karlos Esmuz]

hi!

I have the same quiestion and finally i have the answer:

1. That Q is only an english nmemonics to name the output.

2. When, I make a new question to my PLC's teacher and he response me that Q is the same used for the output on logic gates like AND, OR, NOT, etc.

3. Then, I investigate that Q really means "Quantum" emphasizing a discrete state on the Turing Machine. ( https://electronics.stackexchange.com/questions/51625/why-is-the-output-of-stateful-elements-often-named-q#:~:text=8%20Answers&text=Alan%20Turing%20used%20the%20letter,was%20permeating%20the%20scientific%20%C3%A6ther. )

 

Grettings from Colombia!

 

Edited September 1, 2020 by Karlos Esmuz