Help me to design design U-I input for A/D converter with analog switches

[snoopy]

Hi

I need help to design U (0..10V) and I (4..20mA) input for A/D convertor with analog switches controled by microcontroler.

IDea please


regards Bojan

 

[IanP]

Re: analog design U-I

If you need to convert 4-20mA to 0-10V goto:

and take a look at the last schematic digram ..
All what you need to do is to increase the gain of the second opamp from 1.25 to 2.5 ..

Regards,
IanP

 

[snoopy]

Re: analog design U-I

I need analog design for block marked red in attachment.

Univesal input for 4..20mA and 0..10V to A/D conversions controled by PIC

Regards

 

[IanP]

Re: analog design U-I

In this case for 4-20mA input use 250Ω termination (1-5V) and for 0-10V 2:1 two-resistor volage divider (0-5V) ...
Then select a low Ron CMOS switches:
**broken link removed**
You will need two microcontroller pins to control these switches - on for each channel ..

Regards,
IanP

 

[snoopy]

Re: analog design U-I

All this IC have some resistance in ON positions. From few to 250 ohm.
If I use resistor 124 ohm for current measure and switch R ON is 10 ohm.

I think this will couse errors in my measurments. Also I don´t know what will be with resistance temperature drift. I use 25ppm 0.1% tolerance resisitors 124 ohm for current measurments.

Regards
Bojan