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NET Facility Logger: North Walls 7/8

WSU Puyallup Research Extension

Patrick O'Keeffe
Voiland College of Engineering and Architecture
Washington State University

Work Requested

Current Status

  • Reviewed wiring diagram
    • Identifies possible typos
    • Suggests circuit revision for HTM2500 RH measurements (tie DF input low side to earth)
  • Wiring diagram reviewed by PI
    • Returned with some edits
  • On-site visit by PI
    • Review flagged cells... and update wiring diagram
    • Take photos of installation
    • Positively identify each MUX unit
  • Fix-up sensor hardware integration
    • Per discussion with PI, most sensors are resistive (thermistors)
    • Thermistor-based sensors require additional integration circuity → construct resistor half-bridge
    • Multiplexers designed to read consecutive blocks of identical sensors → reorganize sensor input locations

A workable approach to thermistor integration:

Half-bridge (two-wire) thermistor integration

Notes:

  • precision resistor
    • resistive value: 10kOhm is commonly used, reduces impact of lead wire resistance
    • low tolerance: 0.02% (CSI recommended) or 0.1% (spec of Model 107 probe)
    • low temperature coefficient: no more than 5ppm/°C (CSI recommended)
  • excitation voltage
    • CSI typ uses 2VAC
    • some examples used 0.5V
  • temperature polynomial
    • datasheets specify Beta values.. do they also include Steinhart-Hart coefficients?
    • still need to identify "a, b species correction regression coefficients" mentioned in datasheets

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Source code and docs covering NET facility north walls 7/8

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