Signals

areofall · Nov 5, 2002

Hi, I'm doing an assignment on Tranducers connected to PLC's. One task asks why tranducers are connected to PLC's generally provide a : 0-10v dc signal or a 4-20mA signal. why is this?
If you know of any good books which might help it would be a great help!
Thanks

Steve Etter · Nov 5, 2002

Maurice,

I would love to answer your first question directly, but to do so would actually have me doing the assignment for you! I can't, in good conscience do that.

Instead, let me answer this way: Understand what a transducer is and what it is doing. What does it tell you and how? Once you understand this, the answer to your assignment should be apparent.

As far as a good book goes, I would suggest Phil's book .

Once you have come up with an answer to your assignment, please post it. Many of us here will be happy to help once you show that you have given it a real try first.

Hope this helps,
Steve

Rick Densing · Nov 5, 2002

Why 0-10V? I don't really know either. 10V is a nice low, round number, I guess. 4-20mA has some reasoning. Think about the nature of current. Why start at 4mA?

Sean Caldwell · Nov 5, 2002

as far as i know its a non USA thing

along the same lines as our 50Hz power supplies and your 60Hz (it is 60Hz isn't it?) as far as i know anyway

and i must agree with Steve try find out first

Rick Densing · Nov 5, 2002

What do you mean by non-usa thing? I see both methods a lot.

As far as trying to find out- what are we trying to teach him? How to use a search engine or the index in a book?
We should be encouraging the thought process- offer enough to plant the seed and see how it grows.

Mr. Allen Bradley · Nov 5, 2002

Why start at 4 ma?

Why start at 4ma?

Because, if your 4-20ma cable is open, the current drop to 0 ma.

Than, if you are plugged to a plc's, you know immediately that the cable is broke.

Other: 4-20ma can be 0-100% in your plc's. It's easier to calculate with it in some application.

4 = 0%
8 = 25%
12 = 50%
16 = 75%
20 = 100%

Rick Densing · Nov 5, 2002

I meant it as a question for the original poster to think about.

Sean Caldwell · Nov 6, 2002

its also possible that 10v is used just for the ease of the answer. i dunno iv not looked for the answer and do not know it off the top of my head.

the non-usa thing just meant that a few things are different there from in the UK anyway as far as i know i thought the US was different from everywhere but again i may be wrong.

Rick Densing · Nov 6, 2002

I still don't know what you mean. What is different?

Sean Caldwell · Nov 6, 2002

for one our power supplies.

ours comes in at 50 Hz and i have been led to believe yours comes in at a different rate (60Hz i believe).

TimothyMoulder · Nov 6, 2002

It's not the power supply, it's the outlet you plug it into.

US standard AC power transmission is 60 Hz. The plug in your house you use for your toaster is 120VAC, 60Hz

European is 50 Hz. Your american toaster will do funny things, since it does not speak the language.

TM

Sean Caldwell · Nov 6, 2002

thank you i was right sort of (you say outlet i say power supply for want of a better word)

anyway thats what i meant

Rick Densing · Nov 7, 2002

What threw me off was that we were talking about 0-10v and 4-20mA. Those are DC. I wondered where 50 and 60 Hz came from.

andydaoust · Nov 9, 2002

Sean Caldwell said:
thank you i was right sort of (you say outlet i say power supply for want of a better word)

anyway thats what i meant

Don't you mean, means or mains for your supply?

Could 0 to 10VDC just be 0 to 100%? Easy to figure. Bad since zero means 0% and not dead loop.

johnhopps · Nov 9, 2002

I'm not 100% sure about the following, but I think it is correct. pls no emails if it is not.

0 to 10 vdc is an older signal, but is still to be found on some equipment, like an old Chart recordor, ETC..., so the Transducer manufacture's provide it as a type of output offered.

4-20ma is a current signal, which provides NO SIGNAL LOSS thru the transmission lines. Current is same everywhere along the loop.

It has become the Default standard (I Think) in USA.

4ma as the ZERO Value is used so that the device has can be LOOP POWERED by this initial 4ma. (I Think) Hence, it is called a two wire device.

Signals

areofall

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Steve Etter

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Rick Densing

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Sean Caldwell

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Rick Densing

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Mr. Allen Bradley

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Rick Densing

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Sean Caldwell

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Rick Densing

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Sean Caldwell

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