4-20 ma or 0-10vdc

[tmk]

I'm looking for help. My employer (sysint) gives me questions that he knows I don't have the answer for. My homework is to find the answer and get back to him. He will ask everyday untill I get one. This question is about a week old. If I had a choice why would I want a 4-20ma over a 0-10vdc signal? If anyone could point me in the direction for this info I would appreciate it.

[lonboy]

Hint - voltage drops over distance

[klrogers]

What effect does running a control cable near a power cable have on it? be thinking about magnetic fields, good luck, which I had such a boss!

[davem]

Who says the correct answer is 4-20mA? 0-10VDC is much easier to troubleshoot - whether it's as an input, or an output...all it takes to screw up your troubleshooting endeavor is for a tech to switch his leads to mA, but forget to set his meter to mA, stuff voltage into the mA leads, silently blow the internal fuse, then never read a proper mA signal again..."hey! It doesn't work! Replace that sensor..." or better yet "Replace that controller - it's got a blown output..."
Convincing the tech that he should check those hard-to-find little fuses inside his Fluke is a lot harder than using a control signal that easy to troubleshoot in the first place.

Perhaps not the most compelling argument for the 4-20mA-vs-0-10VDC argument, but a valid one.

Besides, since the boss reads this board at least as much as you do, he won't buy this line of reasoning anyway...

[chrisc]

4-20 is less prevelant to line loss and noise. 0-10 is much easier to troubleshoot and read with a meter. I try to standardize on 0-10 whenever possible. I'm sure if sysint is your boss, he'll try to exlain in different logic and try to include LON or Army Corps wherever possible. Just having fun, Sysint!

[joey791]

Im a 0-10VDC man myself but, heres an instrumentation point of view

With a 4-20 signal 4 is your live zero, with 0-10V you start at 0, so if you have a 4-20 input or output and you are reading 0, you know you have a power problem(short version have alot to do tonite)

[techboy]

I myself also prefer 0-10V. You only need a 20 dollar voltmeter to check. And you can always make sure the controller is pumping out 10 V by manualling the output on the computer. (Is it written "manualling"?..he.he.).
-techboy

[md master]

Sysint is gonna bust your yuts for cheatin'.

[sysint]

Originally posted by md master
Sysint is gonna bust your yuts for cheatin'.

He's OK. I told him to post it. I figured you guys would steer him a bunch of different directions.

He's new to controls. He's just a wookie.

Besides, he didn't post my specific question to him so he is still a bit in the dark.

[tmk]

Hey thanks alot fellas! Is there a certian place I can go on the net to read up and deeper into this so then next time I might be able to answer on the spot!!

That would throw him!

Agian thank you very much.

Hey MD Master. Thanks for the warning however he knows I put this up. He thinks it is a great tool to learn from others and to get good web sites for research.

TMK

[tmk]

OK, the question is in what instance would I want to use a 4-20ma over a 0-10vcd.

One would be distance.
Would this have anything to do with a PID loop?!

[sysint]

Try using the "edit" button. Web newbie too.

Anyway, the question was specifically:
No, I'll let him tough it out a little longer. He needs an answer by Friday

[lonboy]

Let's see.... PID is an acronym for Perplexing, Intimidating, and Difficult. In most cases if you leave off the D it works pretty well.....
Now that we have that cleared up, what do you want to drive from the CV output, what and where is your PV input, and how are you adusting the SP?

-Lb