DIY Laser Power Meter

TheMonk said:

[quote author=knimrod link=1200112201/255#258 date=1203477037]I can't discern anything obviously wrong with your assembled PCB..  I suspect either a problem with your LTC1050, your sensor head/cable, or something unseen relating to the assembly.

The only other thing I can think for you to check is to measure the resistance of the sensor head output (disconnected from amp), with and without the cable.  it should measure ~2.3K-2.5K.  If it's infinite, there may be a problem there.

If you like, pack it up and send it to me.  I'll fix it for ya.

Click to expand...

My sensor head is OK it measured 2.28k.

Thanks for the offer to fix it. Amk is sending me a LTC1050, I will replace it first and see what happen.

regards,
TheMonk [/quote]
Knimrod, I sent the DIY board to you to get fix.

Thanks again for your help!

regards,
TheMonk

I got my Coherent Board in today from ebay. Looking at it, I also see that my fuse is blown. Is there any quick/dirty test to see if the sensor head is ok, before I build my LPM, as I am waiting on the parts/pcb???

Anyone?

Thanks

The fuse on my board was blown and my sensor had a bad element - I hope yours fares better.
You can measure the resistance across the sensor. Mine was around infinite i.e. several MegOhms. Should be around 2.5K Ohms I believe.
That doesn't insure it's ok, but it's a good sign.

that sucks i would have told lyntec to refund me some money

acro-ii said:

I got my Coherent Board in today from ebay.  Looking at it, I also see that my fuse is blown.  Is there any quick/dirty test to see if the sensor head is ok, before I build my LPM, as I am waiting on the parts/pcb???

Anyone?

Thanks

Click to expand...

I wouldn't worry. I've gotten 3 boards from Lyntec. Two had blown fuses and one had no fuse at all. All three had good sensors. The fuse is in the +5V PS circuit and doesn't appear to have anything to do with the sensor.

Got my Coherent board today. Thanks RoSSco!

I gave it a quick test with my DMM (it goes to 0.01mA) and the output seemed reasonable for the lasers I tried.

toked323 said:

that sucks i would have told lyntec to refund me some money

Click to expand...

The boards are sold as-is. He wouldn't get a refund

Out of the 24 boards I've purchased not a single one has been bad. so with the recent sales of these boards for mods added to mine, that's upwards to 40 boards with only one head that had been defective. I'd say that's not bad at all!

Well I got everything except the panel meter(still waiting on Ebay meter). I put the circuit together using the PCB from Knimrod and all the parts from the parts list except for I scavenged the op-amp and BNC connector from the coherent board. Put it all together,fired it up and tried out my x-100 that I just got a few days ago. The sheet from Nova said my x-100 is 136 mW peak and 122 avg. My DIY meter had it floating aound 117-128 mW. THat's as close as I could hope for!

THANK YOU KNIMROD! For all the hard work you put into this as far as documentation, getting the PCBs made, and the continued help throughout! This was a great project, I had fun and I learned a LOT!

I'll post pics of mine once I get the panel meter and finish boxing it all up.

Some thoughts.....

I now have the Coherent module and have started to think about an enclosure. I was going to put the thermopile head inside the enclosure, but I wonder if it's better to leave it exposed to ambient air.

Here's my reasoning:

The sensor normally has temperature control/monitoring to adjust for drift as energy is absorbed by the thermopile. In an enclosure more heat would be trapped and the whole mass would start to heat up causing drift. If exposed to open air, the thermal mass would give off more heat to the ambient air.

Now, I believe this observation is only really valid is one is doing longer "run-time" tests with their lasers for doing a plot as it may take some time for the thermal mass of the heatsink to significantly change. Instantaneous power readings should not be an issue.

I would welcome any thoughts and comments on this. Cheers,

Paul

desslok said:

Well I got everything except the panel meter(still waiting on Ebay meter).  I put the circuit together using the PCB from Knimrod and all the parts from the parts list except for I scavenged the op-amp and BNC connector from the coherent board.  Put it all together,fired it up and tried out my x-100 that I just got a few days ago.  The sheet from Nova said my x-100 is 136 mW peak and 122 avg.  My DIY meter had it floating aound 117-128 mW.  THat's as close as I could hope for!

THANK YOU KNIMROD! For all the hard work you put into this as far as documentation, getting the PCBs made, and the continued help throughout!  This was a great project, I had fun and I learned a LOT!

I'll post pics of mine once I get the panel meter and finish boxing it all up.

Click to expand...

I don't know what to say but thank you!  I know from first hand experience over many, many years as a hobbyist, the satisfaction of building something useful and educational.  I'm only too happy to contribute to your experiences.  If anyone really wants to thank me, post more pictures of your creation!  

chimo said:

Some thoughts.....

I now have the Coherent module and have started to think about an enclosure.  I was going to put the thermopile head inside the enclosure, but I wonder if it's better to leave it exposed to ambient air.  

Here's my reasoning:

The sensor normally has temperature control/monitoring to adjust for drift as energy is absorbed by the thermopile. In an enclosure more heat would be trapped and the whole mass would start to heat up causing drift.  If exposed to open air, the thermal mass would give off more heat to the ambient air.  

Now, I believe this observation is only really valid is one is doing longer "run-time" tests with their lasers for doing a plot as it may take some time for the thermal mass of the heatsink to significantly change.  Instantaneous power readings should not be an issue.  

I would welcome any thoughts and comments on this.  Cheers,

Paul

Click to expand...

I think you're 100% right on.  Another factor is the power being measured...  Measuring a sustained 100-300mW of thermal energy is not going to result in the kind of heat accumulation error (drift) you might expect from sustained 1-3W measurements either.  Also, mounting the sensor in an enclosure with other heat producing circuits may exacerbate the measurement drift as the sensor absorbs and accumulates heat from the inside..

Is there any friendly reliable person here, whom i could pay to buy the thermopile for me and send it to me?


I live in Slovenia, and the seller only ships inside the US...


If there is someone here, who also wants one, but doesn't know how to build the circuit, i could do it for them in return.. Even complete assembly in an enclosure with a display is possible.


PM me in one case or the other... Thanks!

What would be the best range for the LCD panel meter? Should it be 2V? (1.999 3 1/2 digits)

I can only find +-199mV in Conrad for 20€, but it's range can be extended to 2V for an additional 5€.. These are expensive..


I found a cheaper LED panel meter, again with the range of +-199mV, but it says it's very easy to extend it's range with only two resistors... I think i'll go with this one. It's only 10€...

if the range of your meter is less than 2V, you can use a simple voltage divider (2 resistors) to get a fraction of the voltage. i don't know why they would charge an extra 5€ for a couple of resistors...
or you could adjust the amp circuit to do the same thing.

I hear ya with the shipping issue. the cheapest shipping from US to Australia is more than the price of the sensor. i know even at that price it is a good deal, but i can't justify it, given how often i will use the thing.

woop said:

if the range of your meter is less than 2V, you can use a simple voltage divider (2 resistors) to get a fraction of the voltage. i don't know why they would charge an extra 5€ for a couple of resistors...
or you could adjust the amp circuit to do the same thing.

Click to expand...

Yeah, i know... This is how it's shown in the LED panel meter.. I just need a 9 MOhm and a 1 MOhm resistor to get the 2V range..
But for the 20€LCD Conrad charges an additional 5€ for individual range extenders, while the same can be done there...

The LCD is a bit smaller than the LED display, but the LED is only half the price...
I need to decide which one to take, since RoSSco is going to buy the thermopile for me and forward it...


What about the decimal dot? In these, it's set at 199.9.. If i extend the range with a voltage divider it will remain there.. In the LED, i can manually move it, but i don't know about the LCD..

I think it would be best to make it dual range... It would be great, to have the possibility of seeing laser powers up to 200mW in 0.1mW resolution...

I hear ya with the shipping issue. the cheapest shipping from US to Australia is more than the price of the sensor. i know even at that price it is a good deal, but i can't justify it, given how often i will use the thing.

Click to expand...

I was just talking about this with roSSco...

Anyway, he said he can remove the thermopile from the circuit, so the package is smaller.. I also hope it makes it lighter..


But thanks for bringing it up.. Didn't even think about it being so expensive.. What kind of shipping was that, that it cost more than the thermopile?
If you're thinking of getting one, you should also contact RoSSco... Unless you already did...