UV-C Sensor

[Paul Moir]

I have a critical application where a failure of a UV bulb if undetected immediately would be somewhat expensive.  We ended up simply monitoring the power going into the bulbs to check their health.  It's hard to keep a measuring type UVC sensor alive when constantly exposed to the intensity needed to get an appreciable kill in a reasonable amount of time.

[Marvo]

Yes Marvo your idea is sound.

You want something like this: https://www.digikey.ca/products/en/sensors-transducers/optical-sensors-photodiodes/543?k=uvc and a transimpedance amplifier.
Note the sharp cut-off at 280nm.

Interesting that the call the supply "20-40W automatic control", I wonder how its modulated? We were using temperature sensing on the glass to shut down the lamp in case the water stops moving, as the water can overheat if you are pumping 40W into it.

Things to watch out for:
- properly water sealing the sensor from the water, sapphire or quartz window can be used
- do not look at or expose your skin to the UV light, even for a short time

This one is looking good as the nasty UV that is taking care of business is in the far UV 250 n meter range. The suggested sensor will not detect near UV from the sun so you will not have to shade it from daylight. It will only see far UV from the sterilizing lamp. Next question is can you buy a Digi-Key Part Number    SD012-UVC-011-ND or equivalent sensor? How to turn that into an alarm? Many here that know how. In the mean time put a new white t-shirt or new white socks next to it. If they glow in the dark chances are the lamp is good. I would ware UV glasses for that test.

I was wondering if I could tax you on a question that is unrelated. In Cape Town did you or your friends know of Sixto Rodriguez and his songs. Did your parents talk of him ?

Yeah, I have a couple of Rodriguez albums, he was something of an icon in this country. Saw him live as well. https://en.wikipedia.org/wiki/Searching_for_Sugar_Man

[_Wim_]

If you put an "UV-bandpass filter" in front of a photodiode (like this for example https://www.ebay.com/itm/UV-Optical-Bandpass-Filter-254BP10-12-5mm-diameter-EB00014T/311641773821?hash=item488f4c16fd:g:WIgAAOSwepJXa~vi) it might be sufficient to decrease the sensitivity to visible light enough, so you can detect the difference in emitted light intensity with a normal photodiode and an transimpendance amplifier. Photodiodes are less sensitive in the UV region, but with your light source, I think you still should be able to detect sufficient UV light, even with the 22% transmittance of the bandpassfilter.

[phil from seattle]

It seems to me that detecting the visible light from fluorescence is the easiest way to go if you want to have an electronic indication of failure.  Though, I think it might be easier just to have way to look at the fluorescent material. No electronics needed.

By the way, I have a similar sterilizer (they call it a UV filter) for my pond and it emits a blue glow around a clear plastic collar at the coupling.  It's really too faint to see in sunlight, though. We know the bulb needs replacing when we get an algae bloom. Perhaps not a good solution for detecting failure in a potable water system...

[Zero999]

If you put an "UV-bandpass filter" in front of a photodiode (like this for example https://www.ebay.com/itm/UV-Optical-Bandpass-Filter-254BP10-12-5mm-diameter-EB00014T/311641773821?hash=item488f4c16fd:g:WIgAAOSwepJXa~vi) it might be sufficient to decrease the sensitivity to visible light enough, so you can detect the difference in emitted light intensity with a normal photodiode and an transimpendance amplifier. Photodiodes are less sensitive in the UV region, but with your light source, I think you still should be able to detect sufficient UV light, even with the 22% transmittance of the bandpassfilter.

The trouble with that is the photodiode's plastic packaging might be opaque to UV.

[mikeselectricstuff]

Seems to me that just sensing the power draw and keeping track of run-hours will cover the vast majority of failure modes very easily.
Glass lamps are a somewhat mature technology, & I'm struggling to think of a failure mode that wouldn't alter the electrical characteristics enough to detect.
 

[John Heath]

Yes Marvo your idea is sound.

You want something like this: https://www.digikey.ca/products/en/sensors-transducers/optical-sensors-photodiodes/543?k=uvc and a transimpedance amplifier.
Note the sharp cut-off at 280nm.

Interesting that the call the supply "20-40W automatic control", I wonder how its modulated? We were using temperature sensing on the glass to shut down the lamp in case the water stops moving, as the water can overheat if you are pumping 40W into it.

Things to watch out for:
- properly water sealing the sensor from the water, sapphire or quartz window can be used
- do not look at or expose your skin to the UV light, even for a short time

This one is looking good as the nasty UV that is taking care of business is in the far UV 250 n meter range. The suggested sensor will not detect near UV from the sun so you will not have to shade it from daylight. It will only see far UV from the sterilizing lamp. Next question is can you buy a Digi-Key Part Number    SD012-UVC-011-ND or equivalent sensor? How to turn that into an alarm? Many here that know how. In the mean time put a new white t-shirt or new white socks next to it. If they glow in the dark chances are the lamp is good. I would ware UV glasses for that test.

I was wondering if I could tax you on a question that is unrelated. In Cape Town did you or your friends know of Sixto Rodriguez and his songs. Did your parents talk of him ?

Yeah, I have a couple of Rodriguez albums, he was something of an icon in this country. Saw him live as well. https://en.wikipedia.org/wiki/Searching_for_Sugar_Man

It still surprises me that he could be a rock star and no know he was a rock star. It was only 10 years ago he was moving furniture to pay the rent. If he only knew he was famous half way around the world. How could that happen today with the internet and all? It is one of those feel good stories. I will close with one of his songs.

 

[Marvo]

I have a critical application where a failure of a UV bulb if undetected immediately would be somewhat expensive.  We ended up simply monitoring the power going into the bulbs to check their health.  It's hard to keep a measuring type UVC sensor alive when constantly exposed to the intensity needed to get an appreciable kill in a reasonable amount of time.

Seems to me that just sensing the power draw and keeping track of run-hours will cover the vast majority of failure modes very easily.
Glass lamps are a somewhat mature technology, & I'm struggling to think of a failure mode that wouldn't alter the electrical characteristics enough to detect.

My first failed attempt was to monitor the current being drawn by the ballast but the difference between normal run current and the current during lamp failure was too small. Maybe I used the wrong current monitor... Would it be better to monitor the current on the output side of the ballast rather than the input side?

[Paul Moir]

I just did a simple peak detector on the input side of some power factor corrected electronic ballasts.  I don't remember the ratio between bulbs out and on but it was quite a lot.  At least 2:1 but I think about 5:1.  You can easily see the bulbs warm up, reach peak power and then start to drop off as they get too warm (no forced cooling).  Each ballast supported about 30W so that might be the difference if you're running a lot less.