X-Authentication-Warning:	delorie.com: mail set sender to geda-user-bounces using -f
X-Recipient:	geda-user AT delorie DOT com
DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed;
	d=gmail.com; s=20120113;
	h=mime-version:sender:in-reply-to:references:date
	:x-google-sender-auth:message-id:subject:from:to:content-type;
	bh=6SM14XHMhAf4lYIpqCixqeEEIt3qhSCfB1a66c5EjmQ=;
	b=QQsHuZA4AUPYzaC1Wo+hDPgeETXpLryHQMUxsrgK8OE6J41bBaSsUk77opIil3FuUK
	hrbOcIHY54F5YtamoT1Y3eVnhGfFyZ5nXhQQvFYmzSKM/hLLTjp5jl4p8HM2zkKUArZS
	dwMCMsYX79cqCUcSdYZDxHM/R9mDO3/y6eJvjpDywpjfE69jdNGpXTOIfh0jYbm3L3k8
	NCX4gzod/qCPJbD3aMpFGdHZsDEdszgRqN2bnTviRSgtmWTjM1Y+3noMdsB3lXCmqJjv
	Gz+es3vE/3b0prOnXc91Hb4CjE6ztf7z29oXSz9hi/qGe6/8w+kXmUHksWdu4pel2Vcp
	RKZQ==
MIME-Version:	1.0
X-Received:	by 10.229.162.209 with SMTP id w17mr108066qcx.42.1369102081996;
	Mon, 20 May 2013 19:08:01 -0700 (PDT)
Sender:	silicon DOT on DOT inspiration AT gmail DOT com
In-Reply-To:	<20130521013029.16526.qmail@stuge.se>
References:	<51970516 DOT 6040101 AT neurotica DOT com>
	<CAL5HA=DVx7-YL=hrUkAzDh18ncWU7ffwmuzyhGUk8dzaZuKzyA AT mail DOT gmail DOT com>
	<5199AB8C DOT 5060501 AT neurotica DOT com>
	<CANDNR8qOPEadaaExuEcYbV_sf=YvXk6b6Zx9xhEVJQkyphFFSA AT mail DOT gmail DOT com>
	<519AB9DC DOT 4060906 AT neurotica DOT com>
	<CAKakQcdG0BwtH9MJ+yBqos2GazXyCGWn8oH7emXnjZMBuvJRxQ AT mail DOT gmail DOT com>
	<20130521013029 DOT 16526 DOT qmail AT stuge DOT se>
Date:	Tue, 21 May 2013 12:08:01 +1000
X-Google-Sender-Auth:	FVENhzD4gS4YESqCjgxsT2LbrQs
Message-ID:	<CAKakQcezZO_Q1DVOUqRz1bqJKWZX=yiu80eaNw310WBv=8Lnpw@mail.gmail.com>
Subject:	Re: [geda-user] ITEAD?
From:	Stephen Ecob <stephen DOT ecob AT sioi DOT com DOT au>
To:	geda-user AT delorie DOT com
Reply-To:	geda-user AT delorie DOT com
Errors-To:	nobody AT delorie DOT com
X-Mailing-List:	geda-user AT delorie DOT com
X-Unsubscribes-To:	listserv AT delorie DOT com

On Tue, May 21, 2013 at 11:30 AM, Peter Stuge <peter AT stuge DOT se> wrote:
> Stephen Ecob wrote:
>> one of the engineers of our "partner" company was very happy to
>> explain how he'd modified it to give better linearity
>
> What were his modifications?
>
> Did he change some of your assumptions in order to accomplish the
> better performance?

The PCA was an isolator for reading current shunts.  The 50mV peak
shunt signal was boosted to about 5V and galvanically isolated.
It was based on a linear optocoupler.  This optocoupler had a small
but significant nonlinearity.  To obtain high accuracy we
characterised this nonlinearity and cancelled it out in SW after the
signal was digitised.

I wish I could say that this linearity correction was hidden away in
our SW and that the IP thieves ended up with inaccurate readings after
"improving" our HW, but unfortunately we put an option in the UI to
turn the nonlinearity cancellation off.
I guess they would have realised what was happening after a bit of
initial confusion, and turned the nonlinearity cancellation off,
yielding an accuracy close to that of our genuine product.
I do hope, though, that they pulled out a bit of hair when they first
realised that their "improved" HW was yielding worse results at the
system level :-)

- Raw text -