Re: Ocelot and temperature sensings

["Jeff Volp" <JeffVolp@xxxxxxx>]

"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote in message
news:3IudnbrTTZ7F7SreRVn-jQ@xxxxxxxxxx
> "Jeff Volp" <JeffVolp@xxxxxxx> wrote in message
>
> <stuff snipped>
>
> > I measure temperature at several locations with a SECU16 and thermistors
> > that cost a couple of bucks each.  See my post on the ADI forum last
June:
> >
> >
>
http://www.appdigsupport.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=7;t=0004
> 39#000000
>
> Yes - that's what I want to do although I am at a loss to understand the
> C-Max code - as usual.
>
> IF Module #1 -SECU16 Thermistor is < 256
> THEN Load Data to: V_Temp1
> THEN V_Temp1 - 107
> THEN V_Temp1 * 117
> THEN V_Temp1 / 170
> THEN V_Temperature = 113
> THEN V_Temperature - V_Temp1
>
> A few questions other than explaining what the above code is doing:

Quick code overview:  A plot of the voltage produced by the
resistor/thermistor network is non-linear, but there is a significant
portion of the curve that is nearly linear.  That linear portion can be
moved up or down in temperature, determined by the value of the fixed
resistor.  The above code converts the actual voltage measurement to degrees
F over that range.  Basically, it removes the offset at 0 degrees, and then
adjusts the scale to produce 1 count per degree F.  The code is a bit
convoluted to maintain accuracy with the 16-bit fixed point calculations.

> 1) What kind of wire and what sort of length limits are involved?

I used just #22 twisted pair.  My longest run must be close to 100 feet.
Length should not be a issue with the SECU16.  A capacitor could always be
added across the thermistor if noise pickup became a problem.

> 2) Will temperature changes affecting the SECU16 enclosure and pull-up
> resistors affect the accuracy of the readings?

The fixed resistor must be reasonably stable, and should be a 50 ppm/C or
better 1% resistor.

> 3) Is there any way to log the readings?

That may be question better addressed to the ADI group.  There have been
some recent discussions regarding just that.

Jeff