force sensor...

[Andrew W. Macfadyen]

John Honnold wrote:

> Daniel:
>
>     Most dynamometers have a strain gauge built in.  How else could you
> measure torque on a water break dyno.?

Simple a spring balance and a torque arm, works on any size of dyno 20 odd
years back I remember doing a lab on the single cylinder prototype for the P
& J type Doxford  slow speed marine engines  --- it was  the height of a 3
story building and the cylinder  bore was measured in metres  and the torque
readings came from just such a simple set up.  The torque was massive it
only did about 80 RPM full out.


>  Most strain gauges have very
> good temperature stability and the fit between the engine and the
> stand.  When the engine pivots, it pulls( or pushes ) on the strain
> gauge.  Measuring across the strain gauage and supplying this value to
> one side of a bridge will give you pretty torque measurement.
>

Your confusing a strain gauge with a load cell using strain gauges. If   use
a bar with strain gauges mounted on it in  loaded straight  compression or
tension you will get poor resolution. What's needed is  to mount the gauges
on  either a member in simple bending or a proven design such as the "S
Block" which uses a combination of bending and design  features which
concentrate the stress.

A resistance strain gauge is a tiny foil made of resistance wire or
semi-conductor which is bonded to the stress bearing component in the
direction of the stress you want to measure.  In the simplest terms:

Strain = change in length/original length

Stress = load/ cross sectional area

and both are related by the Young's modulus  for the material     "E"

Within elastic limits   Young's Modulus = Stress/Strain


 Because the strain gauge is bonded to the structural member it change
length by the same amount when loaded  changing the resistance of the gauge.

> Regards,
>
> John Honnold
>
> Daniel R. Henriksson wrote:
>
> > Sender: diy_efi-owner at esl.eng.ohio-state.edu
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> > From: "Daniel R. Henriksson" <rotax at ludd.luth.se>
> > Received: (rotax at localhost) by sister.ludd.luth.se (8.6.11/8.6.11) id
> > QAA28994 for diy_efi at efi332.eng.ohio-state.edu; Tue, 21 Jul 1998
> > 16:28:12 +0200
> > Message-Id: <199807211428.QAA28994 at sister.ludd.luth.se>
> > Subject: Re: force sensor...
> > To: diy_efi at efi332.eng.ohio-state.edu
> > Date: Tue, 21 Jul 1998 16:28:12 +0200 (MET DST)
> > In-Reply-To: <199807202351.SAA04211 at dfw-ix2.ix.netcom.com> from
> > "xxalexx at ix.netcom.com" at "Jul 20, 98 05:25:03 am"
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> >
> > I recently acuired a water-brake dynamometer.
> > I'm now looking for some force sensing device, to use as a
> > torque-meter,
> > it should be a robust temp compensated one, drag or pull doesn't
> > matter.
> > It should have a voltage or PWM output.
> >
> > Any ideas?
> >
> > Finally i can make some serius mapping of my home efi... ;-)
> >
> > /Daniel