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Rocket_G
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re: X-rays and Photovoltaics
Rocket_G   12/30/2010 1:19:49 AM
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Thanks Parity, ESD-protective encapsulation sounds really interesting. At what airspeed does triboelectric charge become significant? We would need something in liquid thermoset form that doesn't darken under UV (sunlight).

brightfiber
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re: X-rays and Photovoltaics
brightfiber   12/29/2010 6:00:32 AM
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Rich, to break this down to a finer level, 1) Do any of your tags work reliably time after time or do they all fail intermittently? Design issue? 2) If voltage spikes are suspect, inserting a zener diode in the circuit might be an interesting design revision. 3) Going back to electrostatic discharge, if your tags are encapsulated in any non-conductive plastic package like polycarbonate, they will develop charges on the order of 3-5 KV just from air friction leading to ESD events. Using PEEK or similar conductive plastic will dissipate charge collection and ESD events.

sharps_eng
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re: X-rays and Photovoltaics
sharps_eng   12/24/2010 10:40:09 PM
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Since the tags fail during deployment could we be seeing SEU problems due to solar radiation? What altitudes are you logging among similar tags that survive? It also is possible that your stripped-down ultra-light design allows more exposure to radiation than ordinary enclosures.

Jagdish Bisawa
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re: X-rays and Photovoltaics
Jagdish Bisawa   12/24/2010 7:21:15 AM
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Glad to know that Rich ! Would you also post the results of your findings once you are through with them ? It would be an interesting lesson for the design engineers around.

Rocket_G
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re: X-rays and Photovoltaics
Rocket_G   12/23/2010 3:10:07 AM
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Actually we're hoping for some help from the TSA folks at the airport across the street :-)

Rocket_G
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re: X-rays and Photovoltaics
Rocket_G   12/22/2010 3:51:29 PM
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Thanks, zman - the output of the PV cell goes through a 3V LDO regulator before going anywhere else, to prevent overcharging the battery.

zman_tekinsil
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re: X-rays and Photovoltaics
zman_tekinsil   12/22/2010 3:23:21 PM
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The cell is loaded during transit. With X-Ray this may "perhaps" lead to permanent traps that "may affect" the light to electricity conversion efficiency. Also the 0 instead of 1 logic you mensionned may be stuck bits that can be also due to ESD damage internally in addition to the I/O. Side question since the Voc is 4V, I assume the lithium battery is at least 2 diodes voltage-drop below the cell Voc?

zeeglen
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re: X-rays and Photovoltaics
zeeglen   12/22/2010 2:15:53 AM
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"these failures are observed after they've been in use" Possibly moisture getting into them? How are they sealed? Amendment to previous test - immerse some devices in salt water while at the beach. Your downhill ski idea is also a very valid test for simulating the shock and temperature extremes of a bird in flight.

Rocket_G
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re: X-rays and Photovoltaics
Rocket_G   12/21/2010 11:46:01 PM
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The PV cell Voc is 4V, Isc is 50 microamps. The cell is loaded during transit. A diode on the output of the LDO prevents reverse current flow through it. Checking output shorts and opens postmortem is a good idea. Thanks!

zman_tekinsil
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re: X-rays and Photovoltaics
zman_tekinsil   12/21/2010 2:40:46 AM
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You may have several problems that occured durang the cicuit build-up! ESD may be one of the culprits. You maybe able to see the I/Os quality with a voltmeter. ESD may create a short (metal melt from excessive zap). If that the case your data output maybe shorted after the ESD event. As for the X-ray, silicon based PV may survive X-ray pulses if not loaded. I am not sure what you have!. I assume the PV is not loaded (to generate electricity) during transit from FedEx for instance. Finally what is the output voltage spec of the PV (Open circuit voltage Voc, and other!). That diode may act as back to back scheme limiting current flow to the LDO!

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