Electronic Projects, forums and more.

Go Back   Electronic Circuits Projects Diagrams Free > Electronics Forums > Electronic Projects Design/Ideas/Reviews


Electronic Projects Design/Ideas/Reviews Are you building an electronic project or want to? Maybe you need some assistance? Come and submit your electronic questions here and let our experienced members find a solution.

Reply
 
Tools
Old 30th August 2005, 09:48 AM   #1
Default 0-10V, 4-20mA conversion to 0-5V

Hi...
I'm building an electronic project that has to control 4 relays.
I've one input sensor that could be 0-5V, 0-10V or 4-20mA selected with jumpers. My input microcontroller only accept 5V. What i have to do to the others inputs to have accurate results? If i use a voltage divider to the input 0-10V iīll have unprecision results due to error associated to resistances. In my input 4-20mA how i turn in an accurate signal 0-5V?
There are any IC that does that?
Regards
leonel is offline  
Old 30th August 2005, 10:20 AM   #2
Default

Resistors comes in precisions of 5%, 1% ir even lower. I don't think resistors are your problem, more like output impedance.
Anyway, what you need is an opamp in non-inverting configuration with gain of 0.5.
checkmate is offline  
Old 30th August 2005, 01:12 PM   #3
Default

If i understand right, You have 3 outputs from sensor. Why not connect the 0-5V output directly to microcontroller? I mean, the 0-5V is a basic output and the other two contains additional circuits (opamp for 0-5V to 0-10V and 0-10V to 4-20mA). Using the 4-20mA output only reasonable when the distance between devices too long.
So the most precise output is 0-5V.
Sebi is offline  
Old 30th August 2005, 02:18 PM   #4
Default inputs

Sebi, my problem itīs not choose what input shoul i use... My problem itīs that my circuit has to be prepared to the 3 inputs, that are choosen by jumpers.
I agree with the ideia to use the non-inverting amplifier with a 0.5 gain to the 0-10V input.
But to 4-20mA what configuration shoud i use?
leonel is offline  
Old 30th August 2005, 08:34 PM   #5
Default

Analog Devices made a precise transmitter. The receiver is simple.
Attached Thumbnails
0-10V, 4-20mA conversion to 0-5V-4_20to0_5v.gif  
Attached Files
File Type: pdf ad694_.pdf (426.3 KB, 636 views)
Sebi is offline  
Old 31st August 2005, 12:37 PM   #6
Default

What do you think it's best... A simple opamp with a 250 ohm resistor or the upper one?
leonel is offline  
Old 1st September 2005, 01:43 AM   #7
Default

Hi
first of all the 4-20mA should not be converter to 0-5V
using 4mA as base point is with a reason so it should be always converted to 1V-5V
depending on the accuracy requirement you can use a precision resistor of 250 ohm (actually no opamp is required just a current limiting series resistor for AD input will work) but if you can use an opam as buffer it will be good (just it will add some errors so accuracy will reduce a bit depending on what component you use

for 0-10V you can use a precision voltage divider

Just note that even if you use a precision OPAMP the best available its will still have offset voltage and bias current errors
__________________
Instruite
http://www.icesociety.org
=====================
Ideas that work,
Concepts that sell.
=====================
instruite is offline  
Old 1st September 2005, 06:25 PM   #8
Default

Hi...
I build one board with a 0-5V and a 0-10V. The 0-5V works very well with my micro, but i did a voltage divider with R=150ohm (1%) and i don't have my voltage output right. For example if my input is 5V, my output itīs supposed to be 2.5V, but i have 2.2V. It's impedance problems? If i put an opamp with a gain i will not have problems with my output impedance?
leonel is offline  
Old 1st September 2005, 06:36 PM   #9
Default

The problem is with input impedance rather than output impedance. You can use an opamp voltage follower, or a half-gain non-inverting opamp.
checkmate is offline  
Old 2nd September 2005, 12:39 AM   #10
Default

leonel wrote:
Quote:
I build one board with a 0-5V and a 0-10V. The 0-5V works very well with my micro, but i did a voltage divider with R=150ohm (1%) and i don't have my voltage output right. For example if my input is 5V, my output itīs supposed to be 2.5V, but i have 2.2V. It's impedance problems? If i put an opamp with a gain i will not have problems with my output impedance?
150 ohm is too small a value to use for voltage division
You should use a bigger resistor the maximum resistance value will be decided for current requirement for the analog input of the microcontroller.
__________________
Instruite
http://www.icesociety.org
=====================
Ideas that work,
Concepts that sell.
=====================
instruite is offline  
Old 2nd September 2005, 08:21 AM   #11
Default

Initially i had a 510ohm resistor but the difference was bigger... i will try with opamps to see the result!
leonel is offline  
Old 4th September 2005, 04:16 PM   #12
Default

Quote:
Originally Posted by checkmate
Anyway, what you need is an opamp in non-inverting configuration with gain of 0.5.
u better go check out your op-amp theory. a non inverting op amp has to have a minimum gain of 1 to obtain 0.5 gain and no inversion a ptential devider on the input must cut the signal in half !
__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

www.simonsphotography.org.uk/ - My other hobby
www.rushdenrotaract.org.uk/ - make a difference and have fun !


Never buy "Trust" products, all mine broke !!!
Thunderchild is offline  
Old 18th October 2008, 09:00 AM   #13
Default help me

Quote:
Originally Posted by Sebi View Post
Analog Devices made a precise transmitter. The receiver is simple.
thanks for your attachment files.

in your disign, there areresistor zero and resistor span.

please tell me about resistor zero and resistor span.

thank you before..

Last edited by rl_east; 18th October 2008 at 09:01 AM.
rl_east is offline  
Old 18th October 2008, 09:14 AM   #14
Default

Quote:
Originally Posted by rl_east View Post
thanks for your attachment files.

in your disign, there areresistor zero and resistor span.

please tell me about resistor zero and resistor span.

thank you before..
hi,
The thread is years old.

The 'zero' is set to give '0v' on the output for 4mA loop current and the 'span' is set to give +5V output for 20mA loop current.

Is this what you are asking.?
__________________
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/
ericgibbs is offline  
Old 18th October 2008, 09:20 AM   #15
Default

how we can set resistor to be zero or span?

thank
rl_east is offline  
Reply

Tags
010v, 05v, 420ma, conversion

Thread Tools
Display Modes




All times are GMT. The time now is 02:21 AM.


Electronic Circuits  |  Learning Electronics
eXTReMe Tracker