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Re: Dupla or Dennerle substrate heater cables?

>I'm no engineer but I would think that thermistors would be needed
>instead of, for example, J or K  thermocouples  for the precision
>necessary to detect temp diffs a few inches apart under water. 
>Thermistors' strong points are fine precision while thermocouple excel
>with wide range of temps.  Range isn't much of an issue here.  The
>equipment wouldn't be cheap -- (http://www.omega.com).

Hmm. Since a relative measurement would be OK (difference in degrees from
"heated" to "non-heated" range of water), it would be much cheaper to just
use a bunch of surplus thermistors and some kind of data logger. The
thermistors could be placed in such a way as to be in a line perpidicular
to the cable at a spacing of maybe 1 cm or so and thus be able to measure a
gradient. The data could then be logged over time for the several
thermistors and plotted. I designed an 8-channel, 12-bit resolution
datalogger with 12 but resolution that I use to plot temperatures in our
datacenter. If anyone is interested in seriously looking into UG cable
heating email me off list and I can provide a PCB layout and a programmed
PIC microcontroller for the logger I designed, along with a schematic. It
can be interfaced to a computer using a serial port.

>Question:  Could an aniline dye (such as malachite green) be used to
>assess convction?  How would one control for dissociation or osmotic
>diffusion when trying to measure convection?

I had thought it might be possible to optically measure the diffraction
that is caused by the convection currents around the wire...


Waveform Technology
UNIX Systems Administrator