LPM with Ophir Sensor from nospin - Awesome!

The Thermopile can be configured in 4 different ways with part changes to adjust the total
range of the head to a max of 20 watts. but it also changes the resolution throughout the scale, I figured 1mw resolution was a must for a hobbyist meter, that then results in a 5 watt total measurable max but still has a >20 watt damage threshold.

Jim

nospin said:

The Thermopile can be configured in 4 different ways with part changes to adjust the total
range of the head to a max of 20 watts. but it also changes the resolution throughout the scale, I figured 1mw resolution was a must for a hobbyist meter, that then results in a 5 watt total measurable max but still has a >20 watt damage threshold.

Jim

Click to expand...

Thanks for the info on that...

Here's another picture with my cell phone to show just how small this very nice enclosure is!

Looks like a pretty decent power meter there....

Is the wood-look fineer mandatory?

Benm

Yes the Enclosures are as you see them

Jim

Re: Ophir LPM from nospin - Awesome!

jayrob said:

I'm amazed how this zero's itself?? I gather it's something to do with this 'built in amplifier'?

Is it something inside the thermal head?

I'm no expert on meters, but if so, then I would take a guess and say that the sensor would need to be outside the electronics box in order for it to zero properly to the same environment that the laser is in.

Just thinking out loud...

I know that you explained it some in your first post, but I would like to know more information on this just for my own education...

So if you have anymore information on this feature, please elaborate!


Good question Jay, the thermopile should not be housed with other sources of heat as this adds calories to the reference heat sink the absorber is measured against.

Jim

Click to expand...

I've looked into one of these Heads and there are only 2 wires from
the Thermopile Disk going to the internal Op Amp PCB..
There are no provisions/connections to sample the main heat dissipating
enclosure/housing. The Kenometer Lites I have which use the same exact
OPHIR Heads do not zero themselves...:thinking:

Any clue as to why not... ????


Jerry

Hmmm... I don't want to take it apart, but I see a plug with 4 wires on the back of the thermal sensor...

I wonder if it is different than what you have there??

Any input on that nospin?

Hey Jay... we do R&D here and curiosity always gets the better of us..

My OPHIR 20C-A Heads have the same 4 pin plug 3 are for powering the
internal PCB (+) (-) and (ground).
The third is the output from the internal PCB that is already calibrated
to 1mV=1mW so all you actually need is a Volt Meter or DMM to have a
fully functioning LPM...

But ours just don't want to Zero by themselves and I have tested
all 4 that we have...:thinking:


Jerry

lasersbee said:

Hey Jay... we do R&D here and curiosity always gets the better of us..

My OPHIR 20C-A Heads have the same 4 pin plug 3 are for powering the
internal PCB (+) (-) and (ground).
The third is the output from the internal PCB that is already calibrated
to 1mV=1mW so all you actually need is a Volt Meter or DMM to have a
fully functioning LPM...

But ours just don't want to Zero by themselves and I have tested
all 4 that we have...


Jerry

Click to expand...

I really don't know much about electronics and stuff, and I would not want to imply anything negative about Kenom's design.

But I did test this meter from nospin in different conditions with good results...

I have to wonder if there is any heat source inside Ken's enclosure??

Is the AC/DC converter inside the enclosure? Or do you just plug a 12 volt DC input in?

Again, I don't know about this stuff, but I just think that with the sensitivity of the thermal head, it would obviously need to be away from any heat source. Even a small heat source.

But say that there is no heat. Would the environment inside the enclosure be slightly different from the environment of the laser? Perhaps that is the difference in whether it can 'automatically zero'??

Because I even took mine out to my car to test the 12 volt cigarette lighter adapter that I bought, and it was warmer inside the car, because it was warm out that day. And it went to zero if about 10 seconds or so...

No Jay... all the tests we did ware with the Head outside the enclosure...
with short leads in case of inductance..
The DC/DC converter and Volt meter in the Lites only draw 60mA...
so there is no heat in the box anyway...

Maybe nospin could shed some light on it....:thinking:


Jerry

The specs sheet for this thermophile says nothing about "zeroing" itself... :thinking:

Someone correct me if I'm wrong, but I think a possible explanation to this phenomenon is the equalization of temperature between the thermophile and its environment. The thermophile measures input heat in mW (mJ/s). Therefore, when the temperature equalizes there is no longer a change in heat to measure, and the reading drops back to zero. Jerry?

-Trevor

Under Ideal conditions over time... I agree...
But all the Coherent and OPHIR Heads (which use the Disk
Themopiles) in the Shop need to be Zeroed because they
all drift.... (electronic component Drift... PS Drift.... Heat Drift...
Ambient Air temp...etc)

But you bring up a good point...
I f I stand in front of an OPHIR thermopile... it picks up my body
heat and displays a few mW...
If I'm testing a 3mW Laser.... I don't want the head to zero itself
while testing to be able to see the reading...
How does the OPHIR Head know it is not a Laser that is creating a
signal that it needs to Zero...:thinking:

Jerry

lasersbee said:

Under Ideal conditions over time... I agree...
But all the Coherent and OPHIR Heads (which use the Disk
Themopiles) in the Shop need to be Zeroed because they
all drift.... (electronic component Drift... PS Drift.... Heat Drift...
Ambient Air temp...etc)

Click to expand...

Ah okay, thanks.

But you bring up a good point...
I f I stand in front of an OPHIR thermopile... it picks up my body
heat and displays a few mW...
If I'm testing a 3mW Laser.... I don't want the head to zero itself
while testing to be able to see the reading...
How does the OPHIR Head know it is not a Laser that is creating a
signal that it needs to Zero...:thinking:

Click to expand...

That is exactly what I'm wondering.

-Trevor

I think there are two different temp sensors inside or something...

And if they are both the same temp, it will zero. But if there is a difference between them, it will measure the difference.

But again, I'm just guessing on this. I communicated with nospin and asked him to check the thread and reply to questions being raised...

So he may have some input on these questions...

Here is how it works

The Thermopile is a very sensitive device, it consists of the absorber which is a very thin graphite disc with a broadband coating on it that absorbs energy over a wide spectrum "190nm to 20um in this case" Behind this disc are junctions of dissimilar metals or semiconductors usually Bismuth-Antimony. And on the other side of the junction is the cold side or the heat sink. When heat is applied to the absorber side a voltage is generated by this temperature offset this is called the Seebeck-effect. This voltage is directly proportional to the radiation on the absorber, then it is amplified and is now measurable.

When the Thermopile is fully temperature equalized and no voltage is being generated the amplifier is zeroed out in calibration to show no voltage.

Once this is done every time the sensor is equalized no voltage is generated and the
meter shows a reading of zero.

If the amplifier is of the highest quality this is easily repeatable within usually 1mw every time

The power supply regulation in this meter is Very Stable that makes a big difference, For instance if the Mains line A/C goes up and down
"which it does" or you make Jayrobs cool DC mod the meter wont change readings.

Jim

nospin said:

When the Thermopile is fully temperature equalized and no voltage is being generated the amplifier is zeroed out in calibration to show no voltage.

Click to expand...

Okay, calibration at the factory.

Once this is done every time the sensor is equalized no voltage is generated and the meter shows a reading of zero.

Click to expand...

Okay, no energy input = no voltage out.

If the amplifier is of the highest quality this is easily repeatable within usually 1mw every time

Click to expand...

What? Are you trying to say that the thermophile head is constantly recalibrating itself?

(And why'd you change it from 1 or 2mW?)

-Trevor