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Old 2nd June 2007, 15:26   #1
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Default Light/Photo sensor needed

Hi.
I am trying to rig a 'time-totaliser' for the number of hours a high-intensity UV light works in my product assembly line.
I have been able to locate a time totaliser LCD counter (Input of 3~30 VDC Welcome to Selec) but to get my hands on a Photo (NOT object detecting Photo-electric) or a light sensor is getting difficult. I have extensively Googled for it but in vain.
Anybody with a controls/automation background able to help me with this?
Cheers

Last edited by Xsailor : 2nd June 2007 at 15:28.
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Old 2nd June 2007, 15:41   #2
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what is you application....do you want to count the number of objects or you just want to see for how much time the UV has lit.....

there can be number of ways to do it...can you be a bit specific so that we can understand what is your requirement
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Old 2nd June 2007, 15:52   #3
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I have seen some webcams available with white light leds on them which light up when there is no light. It turns out that these webcams have a small light sensor on top and on covering this light sensor with your finger the leds light up. If can do a little DIY then you can get a webcam like this (for 400-500 bucks) and open it up to get the light senson.
Another such light sensor is in a mouse with scroller . The scroller has gears and on every little scroll it either blocks the light from a small LED to the light sensor or it lets the light pass though and thats how the scroll motion is detected. you can try that also.
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Old 2nd June 2007, 15:57   #4
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Quote:
Originally Posted by low_bass_makker View Post
what is you application....do you want to count the number of objects or you just want to see for how much time the UV has lit..there can be number of ways to do it...can you be a bit specific so that we can understand what is your requirement
Thanks lbm for the quick reply.
1. Number of parts is not the need - I just need to know the number of hours the bulb 'burned'.
2. I can not use the Mains of the Lamp as a time trigger since the mains is ON 24/7. However, the light 'burns' only when a 0VDC circut is complete (Operator Switch).
3. Not possible to create a AND logic and use both values to trigger the counter as there are times when the UV lamp is not needed in production.
Moreover, i do not wish to let my operators come back saying that 'reading wrong Saar, because I forgot to Switch UV mains off when it was not needed'.

Cheers
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Old 2nd June 2007, 17:06   #5
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You can use a LDR (light depending resistance) to detect the presence of light to make it actuate it....this might help you to get the actual time for which the light was lit....commercial sensors are also available in the market for this purpose...

Banner Engineering - Photoelectric Sensors

Last edited by low_bass_makker : 2nd June 2007 at 17:12.
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Old 2nd June 2007, 19:10   #6
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Xsailer, I do not know wether it will work for you, but there is an open source application which links to a webcam and whenever there is any change in scene it clicks a photo. The change in scene could be a foreign object, a sudden change in lighting etc., This can count number of times.
Apart from that LDR is the best option. Since UV is high energy light, you will get decent amount of resistance change.
You will need to mate it to a timer.
Other option is to put a timer in the power supply of the UV light. So whenever the current flows, the timer counts! Something like a simple electricity meter.
If the current taken by UV light is a constant, you just need to do a simple mathematical computation.
For example, for simplicity if your UV light is 1KWH
In the energy meter you have 1unit, this means your light was on for 1 hour, if the unit was KWh

Last edited by tsk1979 : 2nd June 2007 at 19:12.
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Old 2nd June 2007, 22:22   #7
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Light dependant resistors (LDRs) won't help you? they are easily available and cost less too.
EFY India's first magazine on Electronics news, Products, Components, Industry: electronicsforu.com and http://www.kitsnspares.com/ could of some help to you. (though I am sure you would have already knew about these sources of information and components)
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Old 3rd June 2007, 00:57   #8
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Quote:
Originally Posted by shyamhegde View Post
Light dependant resistors (LDRs) won't help you?
how, why????????????????????????????
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Old 3rd June 2007, 01:02   #9
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Quote:
Originally Posted by low_bass_makker View Post
how, why????????????????????????????
I guess shyaam is saying that LDR can help him ...He is just wondering why is Xsailor not considering using one..
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Old 5th June 2007, 09:45   #10
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Thank you for the responces; much appreciate.
Quote:
Originally Posted by shyamhegde View Post
Light dependant resistors (LDRs) won't help you?
@shyamhegde
@lbm
I do not see any place where I mention that LDRs will not help..wonder where this came from

@tsk1979 (the king of open sorce )
If you could please note points 2 and 3 of my last post, you will see that the process does not allow me to rig a timer directly to the mains or similar.

Coming back to the topic, my machines are CE marked and I follow the CFR regulations rather to the T why I need to be very careful on the type, design and layout of any modifications.
Queries;
a) LDRs will work like a rheostat. Any suggestions on the circuit?
b) A photo meter (similar to ones used to measure exposure in cameras) would be a great option if any body can guide me to a commercial source. These meters usually throw out a small current - very useful to trip a relay and thus incorporate in a circuit.

Cheers

@lbp: did you get my pm?

Last edited by Xsailor : 5th June 2007 at 09:52.
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Old 5th June 2007, 10:04   #11
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Dear Xsailor,

Use LDR as you transducer device, LDR has higher resistance when exposed to light & low or negligible resistance when no light is there.

Connect LDR to a NOT gate(Inverter), which will read high when there is no signal from LDR(that is when your lamp is on), this high signal you can feed into a commercial timer.

So Transducer=LDR, Signal conditioner=NOT GATE, OUTPUT=TIMER

just connect these stages, they are available in market, if do not find one try bhagirath place in old delhi.

simple DIY job.
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