From PICLIST@MITVMA.MIT.EDU Fri Nov 15 10:10:37 2002 Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-7.13) id A89D15C700DC; Fri, 15 Nov 2002 10:10:37 -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 <4.007DD1DA@cherry.ease.lsoft.com>; Fri, 15 Nov 2002 12:56:30 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8d) with spool id 6179 for PICLIST@MITVMA.MIT.EDU; Fri, 15 Nov 2002 12:56:26 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 5900; Fri, 15 Nov 2002 12:55:43 -0500 Received: from b.smtp-out.sonic.net [208.201.224.39] by mitvma.mit.edu (IBM VM SMTP Level 320) via TCP with SMTP ; Fri, 15 Nov 2002 12:55:42 EST X-Comment: mitvma.mit.edu: Mail was sent by b.smtp-out.sonic.net Received: (qmail 29154 invoked from network); 15 Nov 2002 17:55:42 -0000 Received: from sub.sonic.net (208.201.224.8) by b.smtp-out.sonic.net with SMTP; 15 Nov 2002 17:55:42 -0000 Received: from sonic.net (bolt [208.201.242.18]) by sub.sonic.net (8.11.6/8.8.5) with ESMTP id gAFHtgC16879 for ; Fri, 15 Nov 2002 09:55:42 -0800 X-envelope-info: Received: from bolt.sonic.net (IDENT:bblick@localhost [127.0.0.1]) by sonic.net (8.12.1/8.12.1) with ESMTP id gAFHtgUH014126 for ; Fri, 15 Nov 2002 09:55:42 -0800 Received: from localhost (bblick@localhost) by bolt.sonic.net (8.12.1/8.12.1/Submit) with ESMTP id gAFHtgwG014123 for ; Fri, 15 Nov 2002 09:55:42 -0800 MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Message-ID: Date: Fri, 15 Nov 2002 09:55:41 -0800 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: Bob Blick 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: 277600701 X-Evolution-Source: pop://mailinglist%40farcite.net@mail.farcite.net/ X-Evolution: 0000078b-0000 > 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. This sensor appears to be a bridge sensor like many others, so the difference in voltage is what you use, then use their figures to find the pressure. But the voltage you have is at no pressure, so it's offset error you need to subtract out. The data sheet says that typical offset is .2 volts and maximum is .425 volts, so your part has close to typical offset. Sounds like Motorola makes really crappy parts with lots of builtin offset you need to calibrate out. I am used to the MicroSwitch sensors, so don't take what I say as absolute, I just glanced at the Motorola data sheet, which by the way is MPX5010, not MPS5010. > Please assume I am younger than 9 or older than 40 and just a hobbiest. I won't get all Olin on ya! Cheerful regards, Bob -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.