That's right... I said No Calibration required...

We have been playing with the OPHIR 20C-A Thermopiles...
that were on sale on eBay a while back... They were new
surplus old stock heads...
I made a deal with Kenom for a few heads and have some
more from the Kenometer Lite's I purchased from him..

They are the same ones that are used on the Kenometer Pro
and USB series...

These Heads come with a preamplifier and calibration circuit
already built into the Head and comes already Calibrated to
1mV=1mW... You don't even need to calibrate them...

All you need to do is supply a split supply and a Voltmeter..
That's all.... anything else is not really required to have
a reliable calibrated Laser Power Meter...

Here is a parts list to build a ~$100.00 LPM...
(your mileage may vary)

1) 2pc 9Volt Batteries -------- $ 4.00 (we used rechargeables)
2) 1pc DPDT toggle switch --- $ 1.00
3) 1pc DMM--------------------- $10.00
4) 1pc OHPIR 20C-A head -- $40-$150 (used) ($390.00 New)

We checked the current draw from the 9Volt batteries and
with no Laser input and at 1000 mW input each battery needs
to supply only 4.7mA...
The batteries will last quite a while before needing to be
changed or recharged.

You can see the simplicity of the circuit in the pics attached and it
is easy enough to follow..
The only thing that we are not sure of is the Label on one of the
heads (see Photo). It notes the Part Number as 20C-A-1-Y....
Looking at the Data Sheet we found on line...

20C-SH_20C-A_20C.pdf

The 20C-A means it was calibrated at customer selected wavelength...
The -1 means that the output it is 1V/1W
The -Y means that the head was calibrated for YAG 1064nm

That Part Number can only go to 4 Watts Free standing and up
to 5 Watts max with some heatsinking...
If the model number were 20C-.4-Y then... with a lot more heay
sinking the heads could read up to 20 Watts..

Even though they were calibrated for 1064nm... the calibration
seems to work well for our uses...

Now all you need to do is find some OPHIR heads...
BTW... we contacted OPHIR and in quantities of 100pc we can get
them for $250.00 USD each Brand New...

(It is to be noted that the Switch as wired in the Photos is not
correct... The DPDT switch must cut both Battery supplies not
just the common as stated below.)

Jerry

You can contact us at any time on our Website: J.BAUER Electronics

------ No Input ------ 200mW Dilda -- Serial Number

damit......wish i saw this before i made my lpm
and now it needs a new tec o_O
dam
so are u selling them??

No... this is just a quick project that we put together
for the Members here...
If they were for sale they would be in the B/S/T section...


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

dam.....
i sent a useless pm to u then

N/P... I just responded to it...


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

fifty dollars? i want.

How accurate are they compared to die4thing,kenometer,beemeter?

It should be just as accurate. The die4thing and Laserbees are calibrated using a calibrated LPM, and Kenometers use these.

-Trevor

They are as accurate as the calibration... One is not
more accurate than another if the calibration is done
right..

BTW... the total above is a bit higher than $50.00..
and can be over $100.00 if the OPHIR head you find
is expensive..


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

I would recommend getting a DPDT switch to break at least two of the power connections to the head. As it stands now there is still +18v being applied to the head, just with no ground when it is switched off.

Seems like a good project at a reasonable price to me. I don't know the exact specs on all its parts, but it dos seem like a nice diy build as long as the sensors are available.

Obviously you are correct and the unit we took the pics of had
a DPDT switch installed after the pics were taken to cut the 18V
circuit... (fixed the parts list above.. )...
Good catch....


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

so where can we get cheap cheap ophirs?

Try eBay... or do a Google search... or maybe some members here
or on other forums may have one...


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

i shall try get a TEC for my MM LPM. if its a total fail il donate it to landfill and buy one of these when (if) i get enough money

Yes I know, Zombie thread, but with all the talk of DIY LPM I just ordered a OPHIR 20C-A off of Ebay. At least that will give me something to measure my output with. Then maybe I can incorporate into some of the other cool projects here on the board.

boo. hiss. necro-post. I was expecting you to tell me where I can find my $100 LPM.

heheheh Well it is now $205.00 but you can get the OPHIR in Jerrys post here off of Ebay for $205.00. I am sure it was $100.00 a few years ago when this thread started, but you know how it is.

It's not necroposting if you add some useful info
to the old thread like where to get some elusive
build parts for the Thread project today..


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

True Jerry, I agree. There are also these sensors "Ophir OEM Laser Power Meter Sensor for CO2 YAG 60W" and I know the one in the top of this thread is only good for about 5 watts but and the one I have list here is for 60w but I wasn't sure of the wavelength designations so I went ahead and just got the one you recommended in this thread. Would this one have worked as well? The part number is 150C-A-.1-C/ERB

The description says the Absorber is optimized for CO2 (10.6um) and Er:YAG (2.94um) lasers. Other CW or long pulse lasers should be OK as well (non Q-switched lasers).

I'm always on the prowl for an ophir head. bumping a useful thread like this is a good thing IMO. I wasn't actively searching for it but came across it and left with some good info.

No you could not use that Head directly...
It does not output 1V/1W...
That head outputs 0.1V/W and would require a
stable and precise amplifier stage to bring it up
to 1V/1W....


Jerry

You can contact us at any time through our Website: J.BAUER Electronics

Alternatively, you could take note of the calibration of the sensor and calculate actual power by multiplying what the DMM displays.

Trevor

Wow this is a rough forum. I get negative feedback because I revived this thread. That sort of sucks. Oh well nothing I can do about that.

My multimeter also reads millivolts so that wouldn't be a problem. What about the wavelength of the sensor?

Would it be usable in the spectrum we normally use? It indicated the absorber is for CO2 (10.6um) and Er:YAG (2.94um) lasers. Other CW or long pulse lasers should be OK as well (non Q-switched lasers).

That was my concern. I have no problem reading the output if it is reasonably accurate like the one originally recommended at the top of this thread.

It would only be good for higher power lasers though, or so it seams. I mean 5 watts gives me .5 volts instead of a full 5 to deal with on an analog input board. Is that what you mean Jerry. Our ADC if read other than directly would only be using a very low end of an analog input?

First... don't worry about the neg rep... your Rep Powers
under your Avatar will only show once you hit 50 Posts.

Using a DMM that can only read mV would give that head
a resolution of 10mW plus ant DMM errors if the head is
still calibrated.

As I stated above to get a 1mV/1mW output from that head
with a resolution of 1mW you would need to use a stable
an precise amplifier stage.

I'm not sure if those heads are still calibrated in the visible
spectrum like the 20C heads. We've never had on in the
shop.

I find that amusing coming from a guy that is so obsessed
with fractional readings...

Using a calculator would only multiply any values by 10
but the resolution would still be only 10mW. You can easily
do that in your head by moving the decimal point to the
right by one place.


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

Assuming it's calibrated to ±3%, the readings are only rated accurate to ±4.5W at the top of the range. Considering we're using 1.0 - 1.5% of that 150W range with lasers the average hobbyist has, you can't expect a lot of precision. Especially with an old surplus sensor. You've got to verify it with a known, calibrated LPM before you can even remotely trust it.

These factors taken into account, 10mW is more than enough resolution.

I thought you would know that, but I'm glad I could help you out.

Trevor