Confused by the test questions!!

[Alecias1991]

Which of the following input operations require a
conversion to digital form prior to input?

a) disk
b) analog
c) contact closures
d) limit switches

I have already eliminated c) and d). English is not my first language and maybe I don't understand the question correctly. But isn't analog not an input operations?

 

[Operaghost]

I am a native English speaker, and that question doesn't make sense to me either. There needs to be more explained.

If I had to lean one way, it would be toward limit switch or contact closure. With a limit switch its contacts opening or closing voltage signal will be converted to a 1 or a 0 in the PLC. But that would also apply to any contact closure. And an analog signal is sometimes converted to a digital representation when viewed in the PLC. I have no idea what "disk" is supposed to mean. Technically all data stored on computer disk drives is stored as ones and zeroes. But, "disk" and "analog" are not operations. A "contact closure" is an operation.

The "input operations" and "prior to input" has me puzzled too. Such odd wording.

Interested how others read and interpret this

OG

 

[plvlce]

I suspect whoever wrote the question does not understand the distinction between 'digital' and 'discrete'

'Analog' simply means that something is continuously variable, that is to say it is not limited to a finite set of possible values. It could be used as an input or an output.

For example you can determine whether a hydraulic cylinder is extended or retracted by means of limit switches (discrete inputs to your controller), or you could attach a transducer and receive an analog value representative of the cylinder's actual position across its full range of travel.

An analog signal would only require conversion if whatever system you are using does not have analog input(s). If the test provides that information then b) seems like the correct choice, albeit very poorly worded (switches and contacts are discrete, but I would not call them digital.

Lacking actual information about what the input is being fed to, there is no reason to assume such conversion is 'required', so if the test does not provide any such information I would say it's a bad question.

I have no idea where 'disk' comes from.

 

[JordanCClark]

Poorly worded indeed, but an analog input card is an Analog-to-Digital converter.

 

[plvlce]

Poorly worded indeed, but an analog input card is an Anaolog-to-Digital converter.

True, but I would not say an input card is "prior to input"

 

[drbitboy]

I'm a native english speaker and I'm with OG on this one.

Was the question's intent to be so vague that many answers are possible? Is the purpose of this question something about PLCs and/or electronics, or is it some kind of conversation starter regarding communication in writing and reading?

Not to mention that not one of those choices is what I would call an input "operation."

What is the context of this question? PLCs? A panel wired with switches and whatnot? Input to what?

In one sense, they are all analog. Even the disk stores 1s and 0s as a direction or orientation of magnetization of magnetic material, and even that is stored in two sections for each bit, the bit is 1 or 0 depending on whether the direction reverses or not, so the disk head detects any reversal, or not, as an analog value, then passes that value to a 1/0 discriminator e.g. transistor.

Limit switches also supply an analog voltage level, or not, that is measured and then to 1/0 discriminator.

All of those "input operations" pass through one or more 1/0 discriminators before they are available in digital form.

Transistors are analog devices; using them for boolean logic just excludes analog values from the process.

So either all of them either "require a conversion to digital form prior to input," or none of them do.

Until we get to the quantum level, everything is analog.

What the heck does "digital form" mean anyway?

 

[Alecias1991]

the instructor is also not a native speaker. I will skip this question and have him clarify it tomorrow and will keep you posted. Thanks a lot for the responses.

 

[Steve Bailey]

Your best bet is to study the reference material the instructor used. That is most likely the source of the terminology. If the course is based on in-person lectures, you should have been paying attention to the instructor's speech patterns and word choice. If based on videos the instructor has made, review them. That will give you clues about whether "input operations" means signals wired to PLC inputs.

 

[ScottTheEngineer]

Which of the following input operations require a
conversion to digital form prior to input?

a) disk
b) analog
c) contact closures
d) limit switches

I have already eliminated c) and d). English is not my first language and maybe I don't understand the question correctly. But isn't analog not an input operations?

A Disk is digital. No conversion needed. Whether CD, DVD tape or floppy

B Analog requires conversion.
C Contact is digital.
D limit switches are digital.


The question seems pretty straightforward to me.

 

[Operaghost]

The question seems pretty straightforward to me.

I'm glad someone can see what they were getting at. I can see your logic with the wording and options. I definitely did not see it before.

When speaking with the instructor about this question, make sure they understands that you know what those four things are. If necessary describe what each of them are, or what they do. Let them know it is the wording of the question that has you (and several of us) confused. By demonstrating you know what those items are, the instructor will know you have put some effort into it and that perhaps they need to restructure the question.

As someone that has written test questions, it is a lot harder than it seems. Trying to write questions in a second language would be quite challenging.

OG

 

[gbradley]

A Disk is digital. No conversion needed. Whether CD, DVD tape or floppy
....

What about Vinyl?

 

[parky]

perhaps the question is obvious but worded poorly or maybe it's to catch you out, the obvious answer is analogue, this is not digital input but converted to a digital representation of the analogue level or so it seems.
The problem is the wording, "prior to to input", an analogue is not converted to digital prior to input it is the input that is analogue, after input it is converted.
C&D I think are pretty obvious, A is defined as tiny magnetic fields stored digitally as north or south poles, so this is a bit of a conumdrum, although generally assumed to be digital it could be interpreted as converted from fields into digital ones & noughts, however, that is not input to a PLC or digital control board. so again the word "prior" could be confusing.
We know a disk is read in as a stream of digital data, as are switches or contacts, however, analogues are not converted to the input indeed they are converted after input into a digital representation (that is if we are talking about the Actual input).
This brings us back to Peter Nachtway's post earlier, poor or wrongly worded information given for others to give relevant answers.
Very often in exams what the original author wrote seems to them accurate & meaningful, however, as we all know often leads to mis-interpretation.
I'm sure that most of us know some questions are deliberately made to check that the participant is reading the question fully before answering.
An example is:
"Which inputs to a PLC are not digital", (Tick all that are relevant) whereas,
"Which inputs to a PLC are digital".

 

[forqnc]

A Disk is digital. No conversion needed. Whether CD, DVD tape or floppy

B Analog requires conversion.
C Contact is digital.
D limit switches are digital.


The question seems pretty straightforward to me.

+1, our thinking is alike, this is how I read the question, although I understood 'Disk' to be an encoder type digital input.