From owner-freebsd-chat Tue Nov 26 16:31:36 1996 Return-Path: owner-chat Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id QAA11897 for chat-outgoing; Tue, 26 Nov 1996 16:31:36 -0800 (PST) Received: from mail.crl.com (mail.crl.com [165.113.1.22]) by freefall.freebsd.org (8.7.5/8.7.3) with SMTP id QAA11887 for ; Tue, 26 Nov 1996 16:31:27 -0800 (PST) Received: from genesis.atrad.adelaide.edu.au by mail.crl.com with SMTP id AA14265 (5.65c/IDA-1.5 for ); Tue, 26 Nov 1996 16:14:48 -0800 Received: (from msmith@localhost) by genesis.atrad.adelaide.edu.au (8.8.2/8.7.3) id KAA04947; Wed, 27 Nov 1996 10:40:05 +1030 (CST) From: Michael Smith Message-Id: <199611270010.KAA04947@genesis.atrad.adelaide.edu.au> Subject: Re: SCSI A/V drives In-Reply-To: <199611262331.QAA25852@phaeton.artisoft.com> from Terry Lambert at "Nov 26, 96 04:31:02 pm" To: terry@lambert.org (Terry Lambert) Date: Wed, 27 Nov 1996 10:40:05 +1030 (CST) Cc: chat@freebsd.org X-Mailer: ELM [version 2.4ME+ PL28 (25)] Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-chat@freebsd.org X-Loop: FreeBSD.org Precedence: bulk Terry Lambert stands accused of saying: > > Actually, the coefficient of radial expansion for various temperates > could be calculated from knowledge of the materials inside the box to > which you attach your electronics. > > This is something a manufacturer should already know. It makes for a pretty textbook problem, yes. In practice, it's not as simple as you'd like to make out. There are any number of potential heat sources, and their location and effects on the geometry of the unit are best determined by measuring the actual item that you're interested in. If you were correct, drives would have $0.25 temperature sensors and never need to perform thermal recal. > The problem in prediction comes from not knowing the temperature at > the time of format. No, the problem in prediction is much simpler; it's practically impossible. You have to account for the temperature coefficients of the platters, the actuator mechanism, the chassis and the variance in magnetic field strength of the actuator magnet. Given that the temperatures of each of these items are not necessarily directly related to any measurable quantity, you are up shit creek before you even start. > As to putting the thing close enough to the platters: ugh. That would > be a problem, assuming the actual and ambient temperatures were inequal. Aha, the light dawns. Perhaps we'll make a practical engineer out of you yet 8) > Anyway, too much on this subject. 8-). Perhaps; I'm still waiting for someone who actually works for a drive manufacturer to pop up and chew _me_ out on a technicality 8) > Terry Lambert -- ]] Mike Smith, Software Engineer msmith@gsoft.com.au [[ ]] Genesis Software genesis@gsoft.com.au [[ ]] High-speed data acquisition and (GSM mobile) 0411-222-496 [[ ]] realtime instrument control. (ph) +61-8-8267-3493 [[ ]] Unix hardware collector. "Where are your PEZ?" The Tick [[