Re: "Colorimeter"

Don Y <blockedofcourse@foo.invalid> wrote:

On 5/21/2025 6:19 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:
 

Sampling jitter within a window corresponds to spectral resolution;
the more jitter, the wider the range of wavelengths potentially
involved in the sample (over time).  As sampling the detector
is a discrete time event (the interval between samples being the
width of the window), how frequently you do this further defines
the spectral resolution.

 
I was assuming very fast sampling so that the presentation of each line
was captured by many samples, that way the software could sort it out
over a large number of repeated passes.  Keep the hardware simple and
let the software deal with the errors if it can be given enough data to
start with.

 
Are you expecting to frequently sample the entire spectrum in each
"pass" ("revolution")?  Or, walk the sampling window up/down the spectrum
in stages?

I was expecting to sweep the whole spectrum at high speed many times,
then analyse the captured data.  Television-type technology could easily
cope with that data rate from a single photocell.

I.e., how much time are you expecting to spend PROCESSING the sampled
data vs. acquiring more data?

The ratio can be varied by either the user or the designer of the
instrument.  If greater accuracy is required, it will take longer to do
both the capture and the analysis.

[...]

>
E.g., as presented to me, there was no need for calibration against
a reference standard, "flat" response across the spectrum, etc.
 
A "laboratory grade" device likely WOULD impose such specifications.
And, bear an associated (likely high) cost.

Some sort of reference source could be used to generate a known spectrum
every 'n' passes; this would also serve for synchronising purposes.
There would be no need to accurately control the rotational speed as
long as it was steady in the short term.  The reference spectrum would
calibrate the span and the end points; it could also calibrate the
spectral amplitude response of the photo-detector.

A small gas-filled discharge tube, pulsed by an ignition transformer,
would suffice for non-critical calibration.


--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk