Electronics > Projects, Designs, and Technical Stuff
OSHW - 24bit ADC measurement system for voltage references
branadic:
I've finished (soldered the missing parts and cleaned them with ultrasonic and IPA) the boards today. Next step is to flash the microcontroller, to do some test and write a pc software (I guess that will be done in Matlab/Octave). Not to forget to mention that the boards will be packaged, I've choosen Hammond 1455C801.
I made some minor changes in the board files and will update them (first post).
After that the next board will be layouted, the LTC1043 divider.
Feel free to duplicate...
Neganur:
sehr geil, danke! :-+
branadic:
Updated the files in the first post, because the value of C5 in 24 Bit ADC.sch was changed. I also modified the dimension layers in both files somewhat, so that the board better fits into the Hammond cases.
Current status:
I calibrated the NTC of my both ADC boards using a SHT75 reference sensor, but will verify my calibration soon with an environmental chamber again.
After a first 300h preaging periode with extended load on the LT1236LS8 I will measure the current reference voltage and the TC on a Keithley 2002 with an oven. Andreas suggested to use a cross-adapter and to measure the TC with one board heated while the other stays at room temperature. Thats for sure a good possibility if you don't have access to calibrated gear.
I'll than check linearity using the resistor divider board and the voltage reference of both ADC boards, because of the lag for the 2:1 LTC1043 board to do that with my LM399 reference, that is now running for more than one year.
I also started to write a Matlab program, that requests the data via serial interface and display them in a diagram. That works fine up to now. Next step is to build a gui around that code and make it a standalone application.
branadic:
While the voltage reference is still preaged with extended load for another few days until 300h have passed and in most places of germany christian people celebrate "happy cadaver" and the none christian people have a free day too, I decided to do something 'bit off topic to this theme. I started to build myself a small temperature chamber, because our climate chambers at work are in use for the next weeks. Well, no problem at all.
I found all the required parts for that in my home lab, a Styropor box with inner dimensions of 270x165x160mm³ and 30mm wall thickness, a heatsink with a size of 150x150mm², a CPU cooler with fan, a Peltier element with size 40x40mm² 12V/30W, a heater foil and a fitting sheet aluminium, two laser cut D-Sub panels and several D-Sub connectors.
All that is still missing are a few mechanical components, that will be finished by the end of the week.
A solution to read out two SHT25, less then half the price of a SHT75 and somewhat more accurate, via VCOM with additional 3x16 LCD display is currently in progress and will complete the setup.
One SHT25 is to track the chambers temperature, the second one is for the device under test, e.g. the NTC of the ADC board inside its case to calibrate it.
It would have been deluxe if the temperature is controlled via a µC or something similar, but as such controllers are very expensive I will start using one of my lab power supply and set the temperature by manuelly adjust the current on the PSU.
I've also drawn the panels for the Hammond cases and will post them here soon in DXF format. I used the free front panel designer by Schaeffer AG for that purpose. Pictures will follow when finished.
branadic:
It's not yet finished, but here is a picture of my temperature box with heater foil and TEC. A few D-Sub9 connectors as feedthrough the wall.
I will order some pcbs next week and put a small ADC extension board to the batch with PT1000 + AE / Vishay 10K 0.01% 5ppm
eBay auction: #380191504233
Couldn't find PWW available from stock at lower cost.
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