From PICLIST@MITVMA.MIT.EDU Fri Nov 15 12:49:12 2002 Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-7.13) id ADC8157013E; Fri, 15 Nov 2002 12:49:12 -0800 Received: from PEAR.EASE.LSOFT.COM (209.119.0.19) by cherry.ease.lsoft.com (LSMTP for Digital Unix v1.1b) with SMTP id <15.007DD78F@cherry.ease.lsoft.com>; Fri, 15 Nov 2002 15:34:55 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8d) with spool id 8558 for PICLIST@MITVMA.MIT.EDU; Fri, 15 Nov 2002 15:34:44 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 9944; Fri, 15 Nov 2002 15:32:52 -0500 Received: from *unknown [66.17.49.171] by mitvma.mit.edu (IBM VM SMTP Level 320) via TCP with ESMTP ; Fri, 15 Nov 2002 15:32:21 EST X-Warning: mitvma.mit.edu: Could not confirm that host [66.17.49.171] is crystal-ex.crystalengineering.net content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable X-MimeOLE: Produced By Microsoft Exchange V6.0.5762.3 X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: Re: [EE]:Pressure sensor confusion Thread-Index: AcKM1/41RrSiJUTBSFSd6JTbQvPXTQAC4/UQ Message-ID: <04D03E2DF8BDBA4A8439617C9FFF092302B105@crystal-ex.crystalengineering.net> Date: Fri, 15 Nov 2002 12:27:07 -0800 Reply-To: pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU> Sender: pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU> From: Matt Heck <m.heck@CRYSTALENGINEERING.NET> Subject: Re: [EE]:Pressure sensor confusion To: PICLIST@MITVMA.MIT.EDU X-RCPT-TO: <mailinglist@FARCITE.NET> Status: R X-UIDL: 277600730 X-Evolution-Source: pop://mailinglist%40farcite.net@mail.farcite.net/ X-Evolution: 000007a0-0000 > Your measured results look good > (1.845 - 0.243) / 0.45 =3D 3.56 kPa > (1.565 - 0.243) / 0.45 =3D 2.94 kPa > The sensor is specified as +/-5% and these values are within +/-2%. Remember that there may be additional error unless you apply temperature compensation. Also remember that a "linear" part is often only "linear" enough to claim a given tolerance-- some post-processing can still be beneficial-- for example, the devices my company makes correct for both pressure and temperature nonlinearities, allowing us to get pretty nice accuracy. (In fact, should you need gear to CALIBRATE your device, once built, hit our website; we have standalone gear, and some modules intended to plug into a meter.) Pressure sensors with frequency outputs are also available, if that is more convenient for you. You should also read the appropriate temperature and error compensation documents from your vendor. You can squeeze a lot of accuracy out of pressure sensors-- we do-- but it can get very expensive to calibrate them, particularily if you need to do it over temperature, so the first things to do with any pressure metrology project, IMHO, are: 1. Determine the level of accuracy you need. 2. Determine the base accuracy of the sensor. 3. Determine how much time you have available. 4. Pick the improvement that makes the most sense given the amount of time you have available-- analog trim pots, fancy digital stuff, whatever is realistic for your needs and skills. 5. Find a calibrator with at least 2:1 (preferably 4:1) accuracy compared to your target spec that you can calibrate your device accurately. Then, have at it-- once done, calibrate. Once calibrated, check for zero drift, hysteresis, and other undesirable behavior. If found, fix. If you get particularily good at all this, drop me a line... Cheers, Matt Heck Crystal Engineering Corporation http://www.crystanengineering.net -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.