jib77
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Here is the original with the 2nd op-amp properly terminated:
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FrozenGate by Avery
DIY Thermal LPM for under $50
- Thread starter MarioMaster
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Why do you have the Zeroing control on the Input rather
than the output where it belongs...
You can not Zero that LPM by reducing the input signal...:thinking:
Jerry
You can contact us at any time on our Website: J.BAUER Electronics
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I only reconstructed the schematic based on the netlist in the board file. I did not make any changes to where the zeroing is.
The board and schematic is consistant proving my point.
The zeroing appears to work by shifting the tec lower ref.
I didn't look too closely at it.
As for the noise reduction, I feel grounding both inputs on spare opamp will lead to a tiny bit noise driving the output as hard as it can due to no gain set. Remember resistors are noisy so the two inputs will not be equal. By setting it up as a follower of a single reference this is eliminated and gain is set to 1.
Btw, why not make the second opamp do something usefull ?
That said, the layout can be improved a lot too by not having the pots on wrong side of the amp...
The board and schematic is consistant proving my point.
The zeroing appears to work by shifting the tec lower ref.
I didn't look too closely at it.
As for the noise reduction, I feel grounding both inputs on spare opamp will lead to a tiny bit noise driving the output as hard as it can due to no gain set. Remember resistors are noisy so the two inputs will not be equal. By setting it up as a follower of a single reference this is eliminated and gain is set to 1.
Btw, why not make the second opamp do something usefull ?
That said, the layout can be improved a lot too by not having the pots on wrong side of the amp...
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Your drawing proves nothing pertaining to the Zero
Adjust of the LPM..
Not Correct... it is the output that is shifted... Not
the input.
Have a look at the original Drawing in post #353...
That Zero circuit is at the output of the OP Amp...
Yours is at the Input...:thinking:
Your Zero circuit only attenuates the input...
It has absolutely nothing to do with Zeroing the LPM...
Have you actually built your "modified" circuit and tested
it with a TEC mounted on a Heat Sink...
If so... have Laser Calibrated it to be sure your modification
of the input from the TEC is not uncalibrating the LPM
by adjusting the input pot... :thinking:
Jerry
You can contact us at any time on our Website: J.BAUER Electronics
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Sorry Jerry, I think you are confusing my basis for the circuit.
I am just trying to reconstruct it. Basically the images in the first posts are no longer available. Shows up as X'es here. All I found was the brd file.
The BRD has different names than the schematic you guys just posted so it's not compareable at all.
It really doesn't matter. It's not how I'd ever build it.
I am a bit confused by the POT1 and POT2 pins.
I just made a schematic with the same parts and same connections as on the board.
Not sure if the 1.2.8 version is the latest though.
Did MarioMaster hold the scematic file back to sell his design on his site?
I think I'll use an avr on my version though. Then I can compensate for any drift by software and measure ambient and cold side to compensate for the drift.
By exposing a TEC to some tests it's actual responsecurve can be used. The dT is important, but so is the load. When you use a TEC in generator-mode it's power transfer from hot to cold increases with the load. I have used this effect in some other designs before and controlled the load to protect the hot side form overheating. The effect is significant and should not be ignored.
Black-body radiation too can be easily compensated for in a digital version.
A 15x15mm area TEC heated to only 50c would radiate/convect away around 12mW from hot side in 23c air and about 9mW in 30c air. Heat the TEC to 80c and you loose around 27mW in 23c air.
A fanned heatsink on cold-side could also keep the base operatingpoint more even and is important for the effciency of the TEC which drops dramatically when cold side temp increses, thus giving lower readings.
I am just trying to reconstruct it. Basically the images in the first posts are no longer available. Shows up as X'es here. All I found was the brd file.
The BRD has different names than the schematic you guys just posted so it's not compareable at all.
It really doesn't matter. It's not how I'd ever build it.
I am a bit confused by the POT1 and POT2 pins.
I just made a schematic with the same parts and same connections as on the board.
Not sure if the 1.2.8 version is the latest though.
Did MarioMaster hold the scematic file back to sell his design on his site?
I think I'll use an avr on my version though. Then I can compensate for any drift by software and measure ambient and cold side to compensate for the drift.
By exposing a TEC to some tests it's actual responsecurve can be used. The dT is important, but so is the load. When you use a TEC in generator-mode it's power transfer from hot to cold increases with the load. I have used this effect in some other designs before and controlled the load to protect the hot side form overheating. The effect is significant and should not be ignored.
Black-body radiation too can be easily compensated for in a digital version.
A 15x15mm area TEC heated to only 50c would radiate/convect away around 12mW from hot side in 23c air and about 9mW in 30c air. Heat the TEC to 80c and you loose around 27mW in 23c air.
A fanned heatsink on cold-side could also keep the base operatingpoint more even and is important for the effciency of the TEC which drops dramatically when cold side temp increses, thus giving lower readings.
Hmm. I think a AVR based version that plugs into pc is a good idea. Can also log data.
No point wasting money on a display either. Solves the whole issue this circuit originally uses the offset to, for using a small voltmeter as a W(mW) display device.
No point wasting money on a display either. Solves the whole issue this circuit originally uses the offset to, for using a small voltmeter as a W(mW) display device.
qumefox
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The schematics are in this thread. If you'll read the whole thread, you'll see them. They were reposted later after the first ones in the OP vanished. Though Jib's schematic is correct. Yours however.. isn't. regardless of how it was generated. It will not function correctly.
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Never said it would. I said I generated a schematic file for the .brd file in this thread. Which post has a correct brd file if any?
Anyway, I agree it wouldn't work. The other schematic would work nicely though. It doesn't have those odd extra POT pinns either.
Anyway, I agree it wouldn't work. The other schematic would work nicely though. It doesn't have those odd extra POT pinns either.
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I'm not sure... but the schematic in the 1st post strangely
disappeared after his LPM was for sale on his site..:thinking:
There are copies of the circuit scattered in the rest of this
Thread... you will need to read the entire Thread to see
the actual circuit and use descriptions.
I've attached a copy of the original MM Circuit...
Jerry
You can contact us at any time on our Website: J.BAUER Electronics
Attachments
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Thanks Jerry.
I did think it was strange as I did read all the posts, but now the images on page 12 loads again and I can see that there are correct circuits there.
Nobody wants to post their brd/sch files though which is a shame...
Still, I actually have a few small TEC's and stuff so I guess I'll try setting up a rs232 based meter.
I'll use the differential metering function of the avr allowing 1x 20x and 200x amplification. That together with switchable 1.1v and 2.56v reference will give from 2.5mV and up to 5.4µV resolution pr div. Reading ambient temp as well as hot-side temp and using a fixed load should allow estimating the exact point on the loadcurve for the element and compensate for the direct-radiation loss as well.
I did think it was strange as I did read all the posts, but now the images on page 12 loads again and I can see that there are correct circuits there.
Nobody wants to post their brd/sch files though which is a shame...
Still, I actually have a few small TEC's and stuff so I guess I'll try setting up a rs232 based meter.
I'll use the differential metering function of the avr allowing 1x 20x and 200x amplification. That together with switchable 1.1v and 2.56v reference will give from 2.5mV and up to 5.4µV resolution pr div. Reading ambient temp as well as hot-side temp and using a fixed load should allow estimating the exact point on the loadcurve for the element and compensate for the direct-radiation loss as well.
Jufran88
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I have my schematic posted in my DIY LPM thread in my signature.
qumefox
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Well, These are simple non-inverting op-amp amplifier circuits. It doesn't really take a rocket surgeon to come up with a board layout. Schematics are more than enough to replicate this circuit.
Kmor2004
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Not to mention if you want to change componets out, from say..through hole parts to SMD parts, just knowing the schmatic is fine because then you can pick the parts you want to use, and layout the board the way you want it.
Do you really believe that?
Wasting time laying out a circuit from scratch is silly.
Also, Eagle has built in functions for swapping components so if a holemounted one is already there is's quicker to swap to a diff package than doing it from scratch.
If you just want to tweak the board to fit a different connector it's a lot easier if you are supplied with a basis to work from.
Although this if fun and interesting, I'd rather spend the time getting something to work better, than having to redo something already done.
I will be sharing both schematic, layout and programcode for my design later.
Now I just wish I could find all my tiny TECs. Maby I left em at work?
BTW: Calibrating the system could be done without a laserpointer with a known output.
You would need a film power resistor and a variable supply. They come in TO126 TO220 and TO247 sizes and up to 100w.
http://www.amstechnologies.com/fileadmin/amsmedia/downloads/658_MP900_MP9100_Series.pdf
The absorprion-factor for light is ofcource a unknown though, but can possibly be assumed close to 1 with black matte coating?
Wasting time laying out a circuit from scratch is silly.
Also, Eagle has built in functions for swapping components so if a holemounted one is already there is's quicker to swap to a diff package than doing it from scratch.
If you just want to tweak the board to fit a different connector it's a lot easier if you are supplied with a basis to work from.
Although this if fun and interesting, I'd rather spend the time getting something to work better, than having to redo something already done.
I will be sharing both schematic, layout and programcode for my design later.
Now I just wish I could find all my tiny TECs. Maby I left em at work?
BTW: Calibrating the system could be done without a laserpointer with a known output.
You would need a film power resistor and a variable supply. They come in TO126 TO220 and TO247 sizes and up to 100w.
http://www.amstechnologies.com/fileadmin/amsmedia/downloads/658_MP900_MP9100_Series.pdf
The absorprion-factor for light is ofcource a unknown though, but can possibly be assumed close to 1 with black matte coating?
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As far as calibration goes...
Using a laser with a "known output" would require purchasing of such a laser. Not to mention theres no guarantee that the laser will always output the same. Shipping..ect, there many variables that could affect the output of that laser. Not to mention the laser would have to be a decent wattage and over the legal limit.
True... you can use a thermal resistor for calibration... just the issue with that is in order to properly sink the heat from the resistor to the TEC, you would have to use a adhesive or a grease that would destroy the TEC. (Surface contact alone would be a rather poor heat conduction method) Using a grease or adhesive however would void the whole process cause you would have TEC with abunch of crud on it. I suppose you could use thermal grease and then clean the TEC afterwards but that would be a painful process and might not quite have the accuracy. Will have to try that out sometime.
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Everyone isn't in the us...
Anyways, The known wattage may vary just as much as the thermal interface to a heater. I like to use thermal silicone pads at work for such situations. They are very stable and do not leave any residue. They are also verry pliable and one simply cuts them to size.
http://www.stockwell.com/data_sheets/thermal/thermal_mgmt_products.pdf
You also have to remember that you are applying a specific ammount of heat to the hot side, not a specific temperature. Tis makes the C/w rating less important and the dT in the junction doesn't matter. What does matter is that you insulate the top and sides so as not to leak energy that way. You want all your energy to build up in the resistor and transfer through the TEC. The temperature will stabelize based on the c/w of the boundry and the base-conductance of the TEC together with it's load. Higher load on the TEC will mean a lower c/w for it and thus also for the entire stack. (Good to know if stuff gets too hot; Just increase the load on the TEC to cool... We've used it at work but somehow I can't find the numbers for how much of a difference it had on c/w. I'll see if I can find it later.)
Oh, and with my line of work I could just order up a 50W laser from one of our suppliers but the prices I wouldn't dream of it.
Anyways, The known wattage may vary just as much as the thermal interface to a heater. I like to use thermal silicone pads at work for such situations. They are very stable and do not leave any residue. They are also verry pliable and one simply cuts them to size.
http://www.stockwell.com/data_sheets/thermal/thermal_mgmt_products.pdf
You also have to remember that you are applying a specific ammount of heat to the hot side, not a specific temperature. Tis makes the C/w rating less important and the dT in the junction doesn't matter. What does matter is that you insulate the top and sides so as not to leak energy that way. You want all your energy to build up in the resistor and transfer through the TEC. The temperature will stabelize based on the c/w of the boundry and the base-conductance of the TEC together with it's load. Higher load on the TEC will mean a lower c/w for it and thus also for the entire stack. (Good to know if stuff gets too hot; Just increase the load on the TEC to cool... We've used it at work but somehow I can't find the numbers for how much of a difference it had on c/w. I'll see if I can find it later.)
Oh, and with my line of work I could just order up a 50W laser from one of our suppliers but the prices I wouldn't dream of it.