Question: What are these things? (AKA chemist trying not to

[ghostwriter]

Hello all,

Here is my set up, I have 8 photodetectors, I assume they are in fact
photoresistors but am not sure. I have not been able to get a
resistance measurment when I put a multimeter across it, but I get a
voltage when I touch both probes to the hot wire.

These photo-thingagigs connect to what I assume is a constant current
supply. As best I can figure the current supply corrects for noise in
the line(actually I use a knob on the front to correct for noise) and
as the resistance of the photoresisters change the voltage output of
the current supply changes to maintain a constant amperage. A data
logger captures the change in voltage and I use this data to analyase
and compare different samples. If it help this assumes that as the
light hitting the resistor decreases the resistance increases and
forces an increase in voltage.

Here of course is the kicker, this piece of equipment was cobbled
together by our field service group. Nobody here is willing to touch
the thing, and I am down to a single working photodetector. I dont
know if it is likley to be the current supply or the
photoresistors(assuming of course that they are photoresistors), or
for that matter the datalogger or the datacapture software.

My best guess is that I am using photoreistors and they have burnt out
due to time and use. Is this something anyone has seen before? And
since I have been unable to get a resistance reading off of the
working sensor, what am I missing? Is the resistance from a standard
photoresistor to low to measure with a multimeter, I wouldn't think
so, but God knows I have been wrong before.

Any help appreciated.

Ghostwriters

 

[Mark W. Lund, PhD]

On a kinder note, this discription could be for almost any type
of a solid state photodetector. It would be helpful if you could
take some pictures, post them on a web site, and let us know.

Otherwise are there any part numbers on the photodetectors?

Best regards
mark

ghostwriter wrote:

Hello all,

Here is my set up, I have 8 photodetectors, I assume they are in fact
photoresistors but am not sure. I have not been able to get a
resistance measurment when I put a multimeter across it, but I get a
voltage when I touch both probes to the hot wire.

These photo-thingagigs connect to what I assume is a constant current
supply. As best I can figure the current supply corrects for noise in
the line(actually I use a knob on the front to correct for noise) and
as the resistance of the photoresisters change the voltage output of
the current supply changes to maintain a constant amperage. A data
logger captures the change in voltage and I use this data to analyase
and compare different samples. If it help this assumes that as the
light hitting the resistor decreases the resistance increases and
forces an increase in voltage.

Here of course is the kicker, this piece of equipment was cobbled
together by our field service group. Nobody here is willing to touch
the thing, and I am down to a single working photodetector. I dont
know if it is likley to be the current supply or the
photoresistors(assuming of course that they are photoresistors), or
for that matter the datalogger or the datacapture software.

My best guess is that I am using photoreistors and they have burnt out
due to time and use. Is this something anyone has seen before? And
since I have been unable to get a resistance reading off of the
working sensor, what am I missing? Is the resistance from a standard
photoresistor to low to measure with a multimeter, I wouldn't think
so, but God knows I have been wrong before.

Any help appreciated.

Ghostwriters

--
----------------------------------------------------------------------
Mark W. Lund, PhD ** Battery Chargers
CEO ** Bulk Cells and Custom Battery Packs
PowerStream Technology ** Custom Power Supplies
140 S. Mountainway Drive ** DC/DC Converters
Orem Utah 84058 ** Custom UPS
http://www.PowerStream.com ** Engineering, manufacturing, consulting

 

[ghostwriter]

Robert Baer <robertbaer@earthlink.net> wrote in message news:<419B1042.63D8EBD9@earthlink.net>...

Well, i have been an electronic technician for over 50 years, and can
say that, for all practical purposed that you know almost nothing about
electronics or electronic components of any type.

Very true, 90% of my knowledge in the subject is electrochemical
theory and the remainder is dominated by black box understanding of
the capacities of electrical equipment.

At least someone pointed to one box and said "this is a power supply"
and the detectors and said "these aer photodectors"
And you have "dug into the guts" enough to be "dangerous".
From your description, i cannot say if you have photoresistors,
photodiodes, or some other tyoe of photo detector.

They are in fact photoresisters. And after finding a meter with a
high enough resolution I was able to determine that they had in fact
worn out due to use. I realized that since my small multimeter was
reading an open circuit that I needed to go up in resolution not down.
Exposure to varying levels of light let me create comparison curves
and at that point it was obvious that the problem was in the
photoresisters.

The same goes with the supply, except it is rare to find a constant
current supply in use.

Again true, it is a constant voltage supply, wired so that a variable
resister can be used to remove noise from the line then run though a
digital Amperage meter that generates a voltage signal that is
captured by a datalogging card and sent into a NI Virtualbench data
management suite.

The "nobody is willing to touch it" would seem to mean that they know
less than you do.
And if the equipment is slowly falling apart and there are no local
repair options in sight, then it would seem that you are beating a dead
horse.

I have ordered the photoresisters and will wait to see how it goes
from here.

You give no clues as to the use(es), sensitivities, spectral needs, or
any thing else of interest - except the hint that it has some kind of
data digitizing capabilities, which something else then reads, logs and
maybe analyzes (clue: software).
I most likely could fix it, and maybe even find a more reliable way to
do the same detection.

No real need to know too much about the details, I will replace the
resisters with the same make and model. I am primiarly interested in
doing control/experimental comparisons and therefore do not have
specific specs for the results. If they are far removed from the older
results I will lose the ability to do cross-comparison between old and
new data, not a huge loss for me.

However, either trash it and get off-the-shelf equipment to do the

job, or forget the whole thing and let someone else "worry" about the
dead project (it is dead if the equipment is dead).

Thanks for the reply.

Ghostwriter