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 i´ll 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
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.
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, my problem it´s not choose what input shoul i use... My problem it´s 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?
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
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 it´s 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?
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 it´s 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.
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 !
The gain of the circuit is set entirely by the 100Ω pot. The 5K pot sets the offset voltage. The voltage gain of the two amplifiers is fixed at 1 each for a total voltage gain of 1. In my view the 100Ω pot should be called GAIN (or SPAN) and the 5K pot should be called OFFSET (or ZERO).
I think the proper way to adjust the circuit is to apply 4 mA and adjust the "zero" and/or "span" pots as necessary to achieve a convenient 0V reference output. Then apply 20 mA and adjust the "zero" pot for a 5V output. That sets the proper gain. Last, apply 4 mA again and set the "span" pot for a 0V output. That sets the proper offset.
Hello! Sebi!
I'm working with the circuit you attached...but I have A problem.. Would you mind if I ask you something?.. I need 0-5 output.
My zero is 1.22V (turning pot 100 ohm to the minimun)..when I fix 5K pot to 5V. What can I do to get zero when de input is 4mA and 5 when 20mA?