Products > Thermal Imaging

(new pic posted, please help) Cairns Viper, self-heating, some other questions

<< < (16/17) > >>

Bill W:
Voltages with and without the peltier connected.  Resistance likely less interesting.

The idea is to work back until we find where the output of a bit of circuit is no longer reasonable when compared to the input.
The important thought is that 'garbage out' is OK if it is correct for a given 'garbage in'.

The circuit operating principles will be along the lines of any Peltier drive IC even if built from discretes, maybe a micro, and (op-amp+TR) instead of the mosfets.

Maybe see how much of this is in there:
http://www.anderswallin.net/2013/08/tec-drive-prototype/
http://www.anderswallin.net/wp-content/uploads/2013/08/sbea001_tec-drive_v3.png

There will be a comparator (or high gain op-amp) to compare the reference to the sensor temperature feedback
There will be an integrator
You already have the output drive stage (opamp and 4 transistor)


Bill

Logan:
Here's the raw test result for the OP295 on the back of the sensor board:

No TEC, just on
45
154
978
7
10
167
749
350

No TEC, 15min
56
154
972
6
9
166
740
349

TEC on, 3min
4520
2191
2185
6
1451
1448
1775
6140

TEC on, 25min (high temperature warning on)
5890
1513
2189
13
44
985
175
6115

Tested voltage against GND, all numbers are in mV, DC mode. Sequence are pin number defined in official spec sheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/OP295_495.pdf

Bill W:
Ok I'd conclude that:

The 'TEC connected' is in fact power to the device and driver.
(as pin 8 is not 6100 or so unless TEC connected)

Initially the device is working OK (for itself) if not what you would want it to be doing
(pins 2/3 and 5/6 very close, 1 and 7 not at limits)

Does run flat out eventually
(pins 2/3 and 5/6 no longer close, 1 and 7 hit rail)

Now need to find where pins 2, 3, 5 and 6 come from.

Bill

Logan:
Thank you Bill and sorry for the late reply.
Where should I find them? There are too many components...

Bill W:
No idea, you are going to have to look and probe. 
First check if they go to any of the connectors on the PCB (ie come from another PCB) or look to track back the traces.

I'd expect the inverting input on each op-amp to attach to the (joined) emitters of each pair of  the drive transistors very like the attached opamp drive booster.

The non-inverting ones are the interesting one to follow.

Bill

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version