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Strange Artifacts of new LPM's output...

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Atomicrox

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FWIW my Ophir also does the turn-on overshoot and sometimes the turn-off overshoot. I'm not sure if that's due to me moving the lasers while pressing the button. Might be, since any small movement will create that "ringing" effect on the graph.

Anyone with one of those remote wired tail caps?

Would also be interesting to see if this happens on other thermopile LPMs out there..
 



Livinloud

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Anyone with one of those remote wired tail caps?

Would also be interesting to see if this happens on other thermopile LPMs out there..
GREAT IDEA!!!! I have always wanted to invest in a pressure switch but never have. This is great excuse to do it and test results! Give me a few weeks to pay my current bill, order one and have it arrive. Ill post the results for everyne.

BTW with all these bumps, figured there be one response from the OP but listen........................you hear that? Oh yup, nothing! :tinfoil:
 

Trevor

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I've got a pressure switch. I can rig up a test tomorrow.

In the meantime, I need to sleep. Just got back from working at a football game.

Trevor
 

Atomicrox

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Cool, waiting for your results!
Be sure not to move your hand near the "field of vision" of the sensor. It can pick up human heat 1m away very easily... one could even use them as intruder detectors XD
 

ARG

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Lab laser, anyone? :p

I'll set one up tomorrow and see what I get. Having the head and the laser bolted down will give clear results
 

djQUAN

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I have a couple lab lasers (532 and 405), a digital storage oscilloscope and ophir head but don't have access to all until next weekend so I can't do the test until then. I can still do it though if you want so you guys can confirm the output of a plot from a bare ophir and the rubicon.


PS: I like the tags. lol :D
 

Livinloud

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bahahaha I just saw the tags. OMG whoever did that needs a +100
 

Meatball

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Any updates on the lab laser run?

A purely electrical "on" function to the driver might remove this spike - is that the current hypothesis?
 

Trevor

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I got busy and forgot to do it. :eek:

School is currently pretty crazy; may have some time tonight.

Trevor
 

djQUAN

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I don't have access to my toys yet so I can't post any. Maybe tomorrow or the next day.
 

djQUAN

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Something productive to do on a cold, rainy sunday :)

Here's the test setup. I used a 150mW 405nm lab laser. I could have also done it with the 77mW 532 labby but results will be the same anyways.

To ensure absolutely no movement of the laser and the LPM from any button pressing, the laser is turned on and off automatically by a signal generator through the TTL input at 0.03Hz. The oscilloscope is triggered on single sweep so the waveform captured is the only one without any movement from button presses.

It's also pretty cool outside so I didn't have any fan or AC turned on so there are no wind drafts to disturb the TEC readings. I also kept the Ophir cover partially closed to block any air movement on the absorber surface.



Here are the output waveforms. These are from the BNC output of my LPM which is directly connected to the Ophir head output. Sorry about the cursor positions, it may be a little off since it's a little hard to see on the scope.





And for good measure, a 0.1Hz modulation with 2sec/div timing on the DSO



edit: PS: I like the new tags hahaha
 

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djQUAN

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Thanks!
Darn, it just occurred to me that I should have also replicated the "ringing" when holding the laser by hand. It'll have to wait 'till next week though since I'm already away from my toys. :( I'll update this once I get the chance.
 

Atomicrox

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While you're at it try a >1W laser as well, in my experience those have a higher initial overshoot.
 

Trevor

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I did a test with a ~1.3W laser with a pressure switch. Click for large version.



I zeroed the LPM such that it sat at ~25mW, so that overshoot on the falling edge of the signal would be visible.

For the first on/off cycle, the overshoot reached up to 1389mW, then the reading settled back down to ~1340mW. When the laser was turned off, the reading fell down to 17mW before settling back at 25mW. So, it does indeed overshoot for both rapidly rising and rapidly falling values. :)

Trevor
 
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