Electronics
All thermistors are: 235-165-ND: FP 07 FAST TIP PROBE, 150 Kohm, at 25C
AAS-920-267D-Thermometrics-NTC-TypeFP07-041216-web.pdf
self-heating is 1C per 50 uW of power dissipation. Resistance is 150K at room temperature. Still-air thermal time constant is 100 msec.
plot of temperature increase vs. applied voltage across thermistor:
The problem with self-heating is that we are increasingly sensitive to local windspeed rather than temperature. We definitely don't want to exceed one volt across one thermistor, or 2 volts across both of them.
Paper on thermal time constant measurements in still and moving air: [15200426 - Journal of Atmospheric and Oceanic Technology] Time Constant Estimates for Radiosonde Temperature Sensors.pdf
Reference Resistors:
- Replace thermistors in test lines
- All are 5% 150 kOhm resistors
Wiring:
For
- All lines are twisted pair, shielded wires
- For main line (that which includes both thermistors):
- low wire (black wire) is connected to low end of power supply (which can be ground)
- high wire (red wire) is connected to high end of power supply
- Top thermistor in voltage divider configuration is soldered directly into high (red) wire
- Bottom thermistor in voltage divider connects high and low (red and black) wires
- Shield is connected to ground (unattached at the end with the bottom thermistor)
- For sample line (running off of midpoint of thermistor voltage dividers)
ADU Board
Jim's Arduino-based hardware
Arduino Model: MKRZERO
To use on Linux, install Arduino IDE. Next go to Tools > Board: <some-model-name> > Boards Manager...
In the Boards Manager, filter by MKRZERO, and install the Arduino SAMD Board drivers. Change the board model to MKZERO via Tools > Arduino SAMD ... Boards > Arduino MKRZERO.
Next, ensure your user is part of the `uucp` and `dialout` groups via
sudo usermod -a -G dialout -G uucp <user>
If you are unsure what the pointer to the device is, run
sudo dmesg --follow -T
and unplug/plug the device. You should see output with information about the device. You are looking for something like
/dev/ttyACM0
Finally, whenever you plug/unplug the device and get `Permission Denied` errors, add rw permissions to the file
sudo chmod a+rw /dev/ttyACM0
Now you can ingest the serial stream using Python, or in the Arduino IDE via Tools > Serial Monitor.