Electronics
All thermistors are 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
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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
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