> Hello, Dan,
>
> Greater accuracy might be attained by using the fact that
> the unit of conductivity is really microsiemens per
> centimeter, not the microsiemens so commonly used.
>
> The probes can be attached by clips to external probes
> of adjustable and measurable separation. This would
> give a set of data pairs that can span the range of the
> meter scale. A least-squares-fit could then be fitted
> to the data-pair set. The slope of the LSF line would
> have units of microsiemens per centimeter, yielding
> the conductivity to within a proportionality constant.
>
> Matthew
>
> ----- Original Message -----
> From: "Dan Nave" <[email protected]>
> To: <[email protected]>
> Sent: Sunday, October 17, 2004 10:53 PM
> Subject: Re: CS>Hanna Meter Model Number
>
>
> > Ode and Mike,
> >
> > As you indicate, the range that we would use the PWT is at the lower end
> of the
> > meter's range. The accuracy, when calibrated at full scale, along with
> the
> > linearity of the response, makes the error large when compared to the
> smaller
> > readings at the low end of the scale.
> >
> > I would suggest, then, that we increase the accuracy of the readings in
> the
> > range that we will be using them. The way to do this is to calibrate
the
> meter
> > at the maximum uS reading that we are likely to encounter, say,
between
> 25 to
> > 30 uS. This will throw off the accuracy at readings substantially above
> this
> > level, but will increase the accuracy between 0 and 30 uS. So, unless
the
> > linearity of the meter's response between 0 and 30 uS is particularly
bad,
> we
> > would approach an accuracy of near +/- 2% of full scale, with full scale
> being
> > 20 or 30 uS (our new "full scale" value). If the linearity between 0
and
> 30 uS
> > is particularly bad, then we will not achieve this accuracy, and the
> accuracy of
> > the meter with normal calibration will also be bad; in short the meter
> would be
> > useless for our purposes...
> >
> > Dan
> >
> >
> > > Re: CS>Hanna Meter Model Number
> > >
> > > * From: Mike Monett (view other messages by this author)
> > > * Date: Sat, 16 Oct 2004 06:48:15
> > >
> > > Ken, thanks for the good info, especially on controlling
> > > temperature!
> > >
> > > As far as getting two units to agree, the spec is +/-2% of full
> > > scale. This means +/-2ppm, which means one unit could read 4 ppm
> > > higher or lower than another and they would still be in spec. A
> > > slight difference in temperature would increase the discrepancy.
> > >
> > > The problem is the units are design for higher conductivity than we
> > > typically get in cs, so our readings are at the bottom 20% of the
> > > range. This is the least accurate portion. Here's the specs from
> > > Hanna's site:
> > >
> > > Range : 0.1 to 99.9 uS/cm
> > > Resolution : 0.1 uS/cm
> > > Accuracy (@20C/68F) : +/-2% Full Scale
> > >
> > > http://www.hannainst.com/products/testers/pwt.htm
> > >
> > >
> > > Although individual units may differ by more than we would like, one
> > > would hope they would be consistent and repeatable. As far as I can
> > > determine from searching the archives, most people seem to feel the
> > > units are repeatable. I know you have posted seeing different
> > > results, but it is not clear what caused them.
> > >
> > > Best Wishes,
> > >
> > > Mike Monett
> > >
> > >
> > > --
> >
> >
> >
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