We use a 2450 based A/D converter (http://www.aip.de/People/wbittner/1wire/ADWandler.pdf) for Temperature and pressure (air) sensing. The sensors are 4-20mA (industrial, made and calibrated by a local company here in Potsdam, Germany).
But I was never realy happy with the resolution. We have another place where we measure pressure: Using a Vaissala sensor (expensive!) with 0-5V output, and a RS485 16bit 0-10V A/D converter to read it (See the pressure reading on http://www.aip.de/stella/status/status.php) The other pressure is listed there also as "spectrograph room pressure", where you can see the difference in reading (and also the difficulties we are having currently with our 1wire devices in general). I read a recent post about a voltage offset, and I added some 'educated guess' resistance value to the 250Ohms we have installed to compensate for the difference in result, but it again drifts away from the 'real' value. All in all: Not good enough for us (I want to see the half day variations in air pressure which come from the solar radiative pressure, which have about 1hPa=mbar amplitude), but looking at the new page http://owfs.org/index.php?page=voltage-measurement there would have been better choices instead of the ds2450. Michael On Dec 6, 2007 11:17 AM, Rob Conway <[EMAIL PROTECTED]> wrote: > > > This is the cct I constructed..its output is 4-20mA however using a 250ohm > resistor it provides 1 - 5 VDC which I feed into one channel of a DS2450 > A/D. What you guy's are taking about sounds great ...direct connect from > sensor to 1wire input > http://img.photobucket.com/albums/v319/rjconway/4-20.gif > > This cct works ok however was never able to get a full range. 1-5VDC I > measure 1050mm water gauge with a pressure sensor, and it provides a range > of 2.9 - 4.6 VDC. I translate pressure into litres for display of how many > litres are available from a reservoir. > > Would really like to know how this project of yours goes... > > rob > > ----- Original Message ----- > From: Paul Alfille > To: [email protected] > Sent: Wednesday, December 05, 2007 10:55 PM > Subject: Re: [Owfs-developers] Pressure sensing and One Wire sensors > > On Dec 5, 2007 12:17 AM, Gregg C Levine <[EMAIL PROTECTED]> > wrote: > > > > Hello! > > Of course it would have made more sense to state that fact. These are the > > MPX family of sensors first made by Motorola during the beginning of the > > MEMS ideas, now made by Freescale, in fact this pair is the MPX12D type. > > > > > > From the datasheet: http://www.ortodoxism.ro/datasheets/motorola/MPX12DP.pdf > > Full scale: 0-70mV with an offset. > > Now from my table: http://owfs.org/index.php?page=voltage-measurement > The DS2438 has a Vsens (vis) range +-250mV > The DS2761 has a range +- 64mV > Both also have supply voltage and temperature, both are pretty inexpensive. > The DS2761 allows a software bias setting that might be useful. > The DS2761 also stores a "cumulative current" which could be used for > average pressure. It is also more accurate (higher resolution with the > smaller voltage range). > > Paul Alfille > > > ________________________________ > > > ------------------------------------------------------------------------- > SF.Net email is sponsored by: The Future of Linux Business White Paper > from Novell. From the desktop to the data center, Linux is going > mainstream. Let it simplify your IT future. > http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 > > ________________________________ > > > _______________________________________________ > Owfs-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/owfs-developers > > > > > > ------------------------------------------------------------------------- > SF.Net email is sponsored by: The Future of Linux Business White Paper > from Novell. From the desktop to the data center, Linux is going > mainstream. Let it simplify your IT future. > http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 > _______________________________________________ > Owfs-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/owfs-developers > > -- Dr. Michael Weber Astrophysikalisches Institut Potsdam An der Sternwarte 16 D-14482 Potsdam Tel: 0331 7499 632 Fax: 0331 7499 200 email: [EMAIL PROTECTED] ------------------------------------------------------------------------- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 _______________________________________________ Owfs-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/owfs-developers
