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

Hi Dave!

Thanks for the info!  

The current interface does have the distance advantage that I might need so I will carefully consider it. Also the I2C interconnect will work well for the follow on CTs and pulse counters that will be added later.

The thermistor .vs. RTE is cost and the fact that some of them are already in place. It would be a matter of making a case to change out the existing devices.

Thanks again!
Rhys


--- In [email protected], "Dave McLaughlin"  wrote:
>
> 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
>