## PSN-L Email List Message

From: ChrisAtUpw@.......
Date: Thu, 1 Sep 2005 21:57:01 EDT

```In a message dated 01/09/2005, ian@........... writes:

Hi,
one assumption I made was that the mean signal, generated by the  mean mass
is subtracted and you are then only measuring the changes.  If  some piezo
sensor can withstand a load generated by 44 Kg (2 supports), then 2  of them might
give the required signal.  By electrically differencing the  signals from the
2 piezo sensors, the remainder is the changing mass +  noise.  Just a
thought...
Hi Ian,

I don't really see why you need such a large  pipe, when something nearer
1" would do fine. If you put on larger diameter  end pots, you increase the
period.
Trying to match up two sensors allowing  for temperature coefficients and
drifts just doesn't work to better than  about 0.1%.
When it is dead easy to measure water levels to  microns, why bother with
weight sensors? The inexpensive piezo sensors  drift in output voltage with
temperature.
There re plenty of problems in making precision  measurements. 'Doing
things the hard way' is just plain dumb.

Regards,

Chris Chapman

In a message dated 01/09/2005, ian@........... writes:
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20
size=3D2>Hi,one assumption I made was that the mean signal, generated=20=
by the=20
mean mass is subtracted and you are then only measuring the changes. =
If=20
some piezo sensor can withstand a load generated by 44 Kg (2 supports), th=
en 2=20
of them might give the required signal.  By electrically differencing=
the=20
signals from the 2 piezo sensors, the remainder is the changing mass +=20
noise.  Just a thought...
Hi Ian,

I don't really see why you need such a larg=
e=20
pipe, when something nearer 1" would do fine. If you put on larger diam=
eter=20
end pots, you increase the period.
Trying to match up two sensors allowing=20
for temperature coefficients and drifts just doesn't work to better tha=
n=20
When it is dead easy to measure water level=
s to=20
microns, why bother with weight sensors? The inexpensive piezo sensors=20
drift in output voltage with temperature.
There re plenty of problems in making preci=
sion=20
measurements. 'Doing things the hard way' is just plain dumb.

Regards,

Chris Chapman

```