At 07:13 AM 5/29/01 -0400, Bob wrote:
> > Foam is quite reflective.
>
>Yeah, it _is_ white, after all. :-)

I was going to add that to the line, but it seemed a bit much after
mentioning "red spot" and "quite reflective".

A wavelength bandpass filter over the receiver and a LED transmitter would
also be helpful.

The weak point with all of these ideas lies with the real world: If you've
ever had to clean an expresso machine, you'd notice how coffer and milk
splatters all over everything. How will any sensor system be kept
operational over time?

Conductivity and other contact-based methods have the hygiene issue to
contend with. So you've got a CIP problem to also solve.

Another possibility is to use a temperature sensor. When the headspace
becomes reduced because of the froth, the temperature of the air above may
be a reliable indicator of fill level. Another possibility is a 0-100% RH
sensor, since the headspace humidity may be usable with a threshold.

Of course, as I believe was already mentioned, if you design the mechanical
part of the system correctly, the electronics becomes simpler: just measure
weight or volume dispensed, since the system fills consistently enough.
This method is simple enough to work by time alone and is practical in the
field.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral@lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

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