Power Meter Calibration and Comparison

The water cooling plug is the larger threaded hole on these. These are all the same. Coherent thermopiles that came from the same ebayer. Although how you came up with the thermopile model # is beyond me. I've even searched for the model you provided and found nothing. That plate on the back is a heater plate and each and every one of these (that came from ebay) has them. Designed to heat the backplate to offset any temperature variation. I doubt that anybody modified this sensor as they all have the bnc connector and the backplate as well. I could have shown you pictures of 20+ of them at one point.

IgorT said:

Your thermopile looks the same as the one i have in my meter.. Did you get yours on the Coherent board from e-bay?
Mine even has the same scratch in the same spot.. Mine also has the BNC connector and the heater plate on the back. I didn't see any water cooling canal tho..

What kind of amplifier are you using? I have a single op-amp circuit at the moment, but i am replacing it with a three op-amp circuit before the calibration, so that the gain won't be affected by the offset anymore. It's not much, but it will be a little bit better.

Click to expand...

I got it from another forum member, who got it from... another forum member.

I think they are modified by this ebayer, whatever he did to them, maybe they're rejected units from his profession, who knows. My lab at home is full of stuff that my father disqualified /9is that the right word?) as a lab equipment repairer/calibrator/tester.

My circuit is a one opamp circuit with LTC1050 and I'm in the process of designing a four-opamp circuit (one opamp creates the ground signal so I can use a single battery). I attached the original schematic (which I modified slightly). Is your amplifier like this?

One of the modifications was changing the series resistor of the zeroing pot from 100k to 1M. This not only increased the precision tenfold (and reduced the range, but still big enough) but also decreased the amplification error.

[edit] Kenom, Whoops, typo, I meant PM10-19C, as in the photo (too small to be readable but definitely not P10-19C)

This is the current version of my ever evolving power meter schematic. I still have a lot of thinking, soldering and testing to go before finalizing my design. Any suggestions are welcome. I'm also open to adopting your circuit if you feel it's better than this one.

Zom-B said:

I got it from another forum member, who got it from... another forum member.

Click to expand...

I have read those very words once before. They were talking about crabs though.

Zom-B said:

[quote author=IgorT link=1217029972/380#383 date=1218988694]Your thermopile looks the same as the one i have in my meter.. Did you get yours on the Coherent board from e-bay?
Mine even has the same scratch in the same spot.. Mine also has the BNC connector and the heater plate on the back. I didn't see any water cooling canal tho..

What kind of amplifier are you using? I have a single op-amp circuit at the moment, but i am replacing it with a three op-amp circuit before the calibration, so that the gain won't be affected by the offset anymore. It's not much, but it will be a little bit better.

Click to expand...

I got it from another forum member, who got it from... another forum member.

I think they are modified by this ebayer, whatever he did to them, maybe they're rejected units from his profession, who knows. My lab at home is full of stuff that my father disqualified /9is that the right word?) as a lab equipment repairer/calibrator/tester.

My circuit is a one opamp circuit with LTC1050 and I'm in the process of designing a four-opamp circuit (one opamp creates the ground signal so I can use a single battery). I attached the original schematic (which I modified slightly). Is your amplifier like this?

One of the modifications was changing the series resistor of the zeroing pot from 100k to 1M. This not only increased the precision tenfold (and reduced the range, but still big enough) but also decreased the amplification error.

[edit] Kenom, Whoops, typo, I meant PM10-19C, as in the photo (too small to be readable but definitely not P10-19C)[/quote]

I dealt with the buyer on ebay personally many times (even got a better deal than anybody else) and he indicated he purchased the units directly from coherent as surplus stuff that never got used. There was no modification done by him at all.
He had no clue what to even do with them hence the unloading them on ebay.

Hey Kenom, I've been talking with Coherent about calibration of my PM5200 meter and PM3 sensor. They are in Oregon (just a couple of days shipping from me), I am probably going to send my meter and sensor to them just because I want it dialed in. Plus, they will repair the analog needle too! The digital read works just fine, but I might as well have them make it like new.

The turn around time is 2 weeks. So, I think I will have time to do this before I get the test lasers. I may have to move my name down the list of California participants. Since there are many of us in CA, it shouldn't be a problem. So I hope you guys are ok with this idea...
Jay

Edit: Nevermind! They want too much... I think it is working good. So, I will use this experiment of ours to check calibration. Then, if necessary, I will send it to them.

Zom-B said:

I think they are modified by this ebayer, whatever he did to them, maybe they're rejected units from his profession, who knows.

My circuit is a one opamp circuit with LTC1050 and I'm in the process of designing a four-opamp circuit (one opamp creates the ground signal so I can use a single battery). I attached the original schematic (which I modified slightly). Is your amplifier like this?

Click to expand...

I also don't think the thermopiles were modified in any way.. If you would see the entire board with the thermopile, i think you would agree.


The amplifier i'm using at the moment is the LTC circuit drawn by Knimrod. Like the first one you posted. I also have 1M there, to minimise the gain error.

The three op-amp circuit is not mine tho. Phenol is making it for me, cos i'm giving him a thermal sensor..


About your four op-amp circuit.. I'll drop you a PM, so we don't pollute this thread with circuits..

Yes, I just found this long forgotten thread http://www.laserpointerforums.com/forums/YaBB.pl?num=1200112201 and it looks like it's the same kind of meter I have, except I have a different case and different display. Even the PCB layout is identical. I wonder Who bought this from him, as I don't see LarryQ in the buyers list. This makes my laser at least fourth-hand

A photo of my meter with modifications

I think that may have been bought ready made from Knimrod directly.. He made them like that.

I think that may have been bought ready made from Knimrod directly.. He made them like that.

I think that may have been bought ready made from Knimrod directly.. He made them like that.

Ok, I've gotten my scientech back and will be doing some additional testing tonight with the test lasers to see how they match up with my initial readings.

Kenom said:

Ok, I've gotten my scientech back and will be doing some additional testing tonight with the test lasers to see how they match up with my initial readings.

Click to expand...

Woot.

Everything is good to go. There was a slight variation between the two meters but was only 2-3mw. I marked the bluray at 92mw and the red at 125mw. They hit the mail tomorrow to be shipped to psuedonemon137 for verification, then on down the loop.

Good news Kenom!

Man, I have noticed how sensitive my PM3 sensor is... Are you sending the thermometer too? Maybe we should make even a separate column in the Google form for temperature?? That way we will be reminded to record that very important information...
Jay

Oh! You already did!

I'm including the thermometer. This IS NOT anyone's to keep. I want that baby back. (not that it was that expensive) Oh and jay, you did want me to move you to the end of the california list still yes?