Just out of curiosity... Why did you go SMD rather thanI finally got the LPM PCB's from China, after a 2 month wait (MakePCB.com, really good quality and price but takes forever and you do not get any updates). On the same day I got another order I placed 2 weeks ago from a domestic source.
What board.... :thinking:Because he was planning on heat-sinking the board?
Nice clean idea in theory.... but..Mostly for size ... I wanted to make it small enough to mount it on the TO220 heatsink opposite the TEC.
The majority of the heat should be dissipated into the fins, as opposed to the back of the heatsink.Nice clean idea in theory.... but..
Sorry to say....Not a good Idea...IMO
The fiberglass PCB will act as an insulator and slow the
heat dissipation speed of the Heat Sink.
I wouldn't recommend it if you want your LPM to be as
accurate as possible..
Just like we do not recommend installing Thermopiles into
enclosures... the heat generated by the Laser Beam has
nowhere to go and can throw off readings...
Even more so with the 445nm beasts that are being built...
BTW... if you are not too worried about accuracy... I'm sure
that will be fine...
Just my $0.02....
If that is indeed the case than a <2mm thick piece of metal may not be the best way to go about it. In the end, the change in temperature would be rather readily felt.^ Uhm, but keep in mind that, for LPM purpose, the main thing that the heatsink have to do is NOT to dissipate heat (this can be the point if the TEC was used as cooler, NOT as sensor) ..... when you use a TEC (or a thermopile, for this) as power sensor, the main purpose of the heatsink is to KEEP the temperature of the "reference" plate as more stable as possible (once all the assembly have reached ambient temperature, before to start the measure, ofcourse) .....
For this purpose, a lot of fins only helps in reaching a stability point at ambient temperature more quickly, but then for KEEP IT STABLE, the more important thing is THE MASS of the heatsink (or, being more precise the THERMAL MASS) ..... can say that, once the assembly is at ambient temperature, a solid block of aluminium or copper is better, for this, than a lot of fins ..... so, in this special case, the fact that the back of the heatsink is enclosed, or don't have air circulation, is almost ininfluent.
I made some LPMs in this way, and a pair of them have the sensor totally enclosed in the box, with the rest ..... once you left them stabilize at ambient temperature, there's no difference in the readings, from them and the "open sensors" ones (ofcourse, you NEED to left them reach stability with ambient temperature, if you carry them from one place to another with different temp, but this is valid also for open types).
A different case happens if you need to make long-times readings of a high power laser beam ..... in this case, the capacity to dissipate the heat transferred from the reading face to the reference face start to become important, too, but in these cases, i usually use big-mass heatsinks with forced air circulation (fan), with the reading face insulated from the airflow ..... the more important thing, for a sensor with that limited thermal mass, is not the presence of the enclosure on the back, is that you don't keep it with your fingers or that you don't place it on a surface with a high thermal conductivity and different temperature than ambient air, like metal plates, for avoid that these things changes the thermal equilibre .....
Yes, but usually that type of sensor is not specifically designed for long-time readings with high power lasers, right ? ..... i mean, is difficult that a home / hobby user needs to do a 5 or 10 minutes sampling on an 1W laser, is more usual to use it for check for instant powers, and this requires usually 15 seconds, or few moew .....If that is indeed the case than a <2mm thick piece of metal may not be the best way to go about it. In the end, the change in temperature would be rather readily felt.
If the back was open, any change in temperature would be readily felt.
If the back was closed, there's no way for air to circulate, hence any temperature difference would be intensified.
:wtf:Whoa... backup it Nelly....The majority of the heat should be dissipated into the fins, as opposed to the back of the heatsink.
If the heat is being dissipated out the back of the heatsink, then the heatsink isn't doing it's job correctly.
The heatsink is meant to remove heat from an object, and allow the heat to dissipate into the ambient air, either by forced ventilation or by natural convection.
If it's simply leaking out the back then it's not working correctly. The heat should be taking the easiest path out, which should be out the fins.
Invariably there will be some heat leaking out the back instead of going into the fins, but the majority of it should be going into the fins.
The only case in which I can see readings being affected is if the board is actively generating heat. The amp should be calibrated to offset that, if that is indeed the case.
Also, care to explain this?
As far as I can see, the back of the thermopile is enclosed, and hermetically sealed.The heat will be dissipated into the air inside the compartment, and will stay there. There's no way air can circulate in that cavity.
Air is a very poor conductor of heat, and that plug cavity makes a much better insulator than the fibreglass board does.
With the fibreglass board, there's a small gap (mounting standoff), and as a result, there'll be (small, but nonetheless existant) convection currents moving between the board and the heatsink.
And before youask, I don't have any hidden agendas. I just find it odd that you suggest the opposite to what you do. Perhaps it was my mistake not to know who Nospin was.