0-10VOLTS AND 4-20 mA

f mc caffrey

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Join Date
Dec 2002
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TRANSDUCERS CONNECTED TO PLC'S GENERALLY PROVIDE A 0-10V SIGNAL OR A 4-20 mA SIGNAL. INVESTIGATE AND EXPLAIN WHY THEY ARE USED

THANKS
 
I believe the instructor wants YOU, not me (us) to investigate.
Asking for an explanation is not investigating.

Hint: the reason has to do with losses.
 
Let's suppose that you were in charge of defining a standard for the signal levels of analog sensors. The amplitude of the signal is to be proportional to the phenomenon being measured.

What characteristics of DC voltage make it an attractive choice for a standard signal? Why a zero to 10 volt range? Why not zero to 100 volts? Why not 3.14159 to 6.0 x 10^23 volts?

What characteristics of DC current make it an attractive choice for a standard signal? Why a 4 - 20 mA range? Why not zero to 100 mA?

Why are both standards in use? Why hasn't one proved superior to the other?
 
Its funny, I never thought about or asked the question "Why 4 to 20ma" but now that this has come up I can see a reason pertaining to plc's but not necessarily appropriate for the non solid state world.

The 0 to 10volt is obvious.

I can only hope the questioner asks more questions and/or posts his findings on the subject. I dont want anyone to post an answer just because of me. I have my ideas and will now research the subject.
 
all I know (only took a paragraph.. ouch)

Hint - I=E/R

Has something to do with the resistance of a loop and the normal supply voltage used.

Why 4ma instead of zero?
- I think it has something to do with the fact that you have to have a functional loop in order to read 0 (4ma) of whatever you are measuring. More robust that way I guess. (back in the day).

How about posting what you find, when you get the questions answered, I wouldn't mind getting my brain jarred loose again. Mann... the memory is fading.

Why is there 0-10V? I never had to use it. Everything I worked with is pretty much 4-20ma. Take that back, have used 0-10V on a drive once, when using a pot. Is it a distance thingy?
 
Damn!

No matter where I go, no matter how hard I try to hide, I just can't seem to get away from that damned "Avagadro's Number!!!"

A POX ON YOU, STEVE!
 
Avagadro's Number:

6.022 x 1023


This is the number of atoms in a "Mole". I always thought it was closer to the number of atoms in a Muskrat, myself.

A "Mole" is a convenient way to do calculations with masses of elements (Elements such as Hydrogen, Helium, etc.)

A "Mole" is an amount of mass (in grams) equal to the Atomic Weight for the given Element. For example, the Atomic Weight of Oxygen is 16. Therefore, 1-Mole of Oxygen has a mass of 16 grams.

1-Mole (16 grams) of Oxygen has 6.022 x 1023 atoms of Oxygen.

1-Mole (14 grams) of Nitrogen has 6.022 x 1023 atoms of Nitrogen.

Please! Don't ask for any deeper explanation... I would then have to delve into the world of "Stoichiometry". Then you would know too many secrets of the Atom, then I'd surely have to kill you... National Security, don't cha know?
 
F McCaffrey,

why do we on the European continent (and others) drive on the right hand side of the road, and the English (and a mere few others) drive on the left hand side? Why do people write names starting with capitals, which is considered polite, and why is the use of capitals on the internet considered as shouting, and thus being rude?

It all has to do with standards and/or agreements. Some of them are simply choices made sometimes in the past, others are based on solutions for certain problems.

It might help you to know that the oldest standards for analog signals were 0-10V and 0-20mA. Later on the standards -10V to +10V and 4-20mA were introduced, which are now commonly used. Ask yourself what could be the reason for this. Consider the distance between the transducer and the PLC. What to do with bidirectional signals? Motor do tend to turn both ways! What if you had to measure their speed? Ask yourself this kind of questions and you'll find the answers yourself.

Kind regards,

Jean Pierre Vandecandelaere
Instructor PLC - SCADA - Basic ICT
VDAB Bruges
Belgium
 
What's an avacado (or it's number--why does an avacado have a number)got to do with process signals, anyhow?? We're not talking guacamole, here, are we??
 
Actually, some o' us old coots will remember 0-5 VDC as being much more popular than 0-10 VDC, and 3-15 psig being pretty common as well! Hint for original question: notice that the 3-15 psig has a 20% "live zero" just like 4-20 mA.

I always wondered if 0-5 VDC was popular because you could get telephone stuff pretty cheap, and telphone stuff was 0-5 VDC because ya could get telegraph stuff pretty cheap. Does anybody know if this is true?
 
Many active or "smart" transmitters are "loop powered". The two signal wires power the device. Whether it's the first 4 mA or not, I don't know.
 

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goodday everyone,could you kindly advise me on how to make a simple 0-10volts simulator for my plc?pls advise tks
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