From PICLIST@MITVMA.MIT.EDU Fri Nov 15 10:18:27 2002 Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-7.13) id AA7316280078; Fri, 15 Nov 2002 10:18:27 -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 <6.007DD0AC@cherry.ease.lsoft.com>; Fri, 15 Nov 2002 13:04:20 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8d) with spool id 6380 for PICLIST@MITVMA.MIT.EDU; Fri, 15 Nov 2002 13:04:15 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 6223; Fri, 15 Nov 2002 13:03:14 -0500 Received: from tomts7-srv.bellnexxia.net [209.226.175.40] by mitvma.mit.edu (IBM VM SMTP Level 320) via TCP with SMTP ; Fri, 15 Nov 2002 13:03:14 EST X-Comment: mitvma.mit.edu: Mail was sent by tomts7-srv.bellnexxia.net Received: from amd1200 ([64.231.204.235]) by tomts7-srv.bellnexxia.net (InterMail vM.5.01.04.19 201-253-122-122-119-20020516) with SMTP id <20021115180314.IGYA27906.tomts7-srv.bellnexxia.net@amd1200> for ; Fri, 15 Nov 2002 13:03:14 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2910.0) Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: Date: Fri, 15 Nov 2002 13:03:10 -0500 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: Herbert Graf Subject: Re: [EE]:Pressure sensor confusion To: PICLIST@MITVMA.MIT.EDU In-Reply-To: <000e01c28cca$41a351e0$36313fd1@xero> X-RCPT-TO: Status: R X-UIDL: 277600702 X-Evolution-Source: pop://mailinglist%40farcite.net@mail.farcite.net/ X-Evolution: 0000078c-0000 > I am having problems figuring out how to use my Motorola pressure > sensor MPS5010dp. > > The offset voltage is .243v. no pressure applied. > I take two seperate vacuum readings: > > 1.845 v = 3.607 Kpa > 1.565 v = 2.992 Kpa > > the difference in Kpa is .615 Kpa. > > But if I take the difference in voltage output = .280 volts, and > calculate the Kpa for the voltage difference I get .1703 Kpa. > > Why is this? I'm not familiar with that sensor but generally they aren't perfectly linear and need quite an "interesting" formula in cases where full swing is necessary. What I did with my (for an atmospheric pressure project) is record the value the sensor put out every hour and recorded the atmospheric pressure reported on our local weather channel. After a few days I had enough info to put those values into Excel and have it apply it's "magic" to generate an equation for me. Turned out to be rather accurate (had to use a 1st order polynomial for best fit). A similar procedure should work in your case. TTYL -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.