RE: Advice for ADC chip(s) selection to work with R6K Rabbit Module?

Hi Rhys,

 

I have a 16 channel system that reads up to fourteen 4-20mA pressure sensors
for depth and one 4-20mA temperature sensor with 0 - 100 deg C range. 

 

I use the MCP3424 from Microchip and it works really well. I use 4 of them
on each board. I use the 16 bit setting and I get 1mm precision on depth
with a 15M depth sensor.

 

They are I2C interface so easy to hook up to the Rabbit.

 

There is a built in 2.5V reference.

 

Just make sure you use good decoupling on the VDD input. I use a 4u7F tant
cap with a 0.1uF ceramic on the VDD pin and a small inductor in series with
the supply. The supply side of the inductor I fit another 0.1uF cap. I get a
very nice stable reading with that setup.

 

I have not used thermistors for temperature before but you will need some
kind of linearisation calculation of calibration to correct to a straight
line. Is there any reason you can't go with RTD and then use 4-20mA
convertor? Is it purely price is the limitation? The 4-20mA means you can
locate the sensor some distance away from your circuit.

 

Good luck

Dave.

 

From: [email protected] [mailto:[email protected]] On
Behalf Of rhysmicrofoundry
Sent: 05 February 2013 12:19
To: [email protected]
Subject: [rabbit-semi] Advice for ADC chip(s) selection to work with R6K
Rabbit Module?

 

  

I am considering a project that requires 16 channels of ADC for temperature
sensors. 

Anybody have experience with a particular chip(s) - successful and not?
Suggestions about single channel - multi chip or single chip - multi channel
implementations? 

Requirement calls for 0.5F accuracy - I am thinking maybe a better quality
thermistors - 20F to 210F range. Comments? 

Also an suggestion about calibration strategy that you have worked with -
good or bad.

Any comments or suggestions welcome! Things to watch out for.

Thanks,
Rhys