Compost WXT520 Logger Program

Simple data acquisition from Vaisala WXT520 using a Campbell Scientific CR1000.

Wiring

The CR1000 is powered from a 12V power supply w/ charging regulator (PS200, Campbell Scientific) and a 7AH gel cell battery. A 20W solar panel recharges the system.

WXT520

See manufacturer (not vendor) user manual for correct color identification.

Description	Color	CR1000
power input	brown	12V
power ground	red	G
SDI-12 data signals	blue & white	C1
SDI-12 ground	green	G
(opt.) heater power	yellow	-
(opt.) heater ground	pink	-
not used	gray	-

Operation

To deploy the unit

1. Mount WXT520 oriented to True North; see user manuals under References below
2. Connect power/data cable to WXT520
3. Turn the PS200 power switch to ON

To monitor in real time

Press any key to wake the keyboard display. Summary values are displayed on the default screen.

To collect data

1. Unscrew and open the memory card cover
2. Press the large white "Removal button"
3. Press the black push tab to eject memory card
4. Insert new blank memory card
5. Close and secure memory card cover

Data Products

The weather station internally produces 1-minute average values and the logger samples those values at the start of each minute. A single data file is written to CompactFlash memory card:

• Base name: compost_WXT520
• Record interval: 5 minutes
• Number of records: approximately 90 days on external memory card (up to 230 days internal storage)
• Fill-stop settings: "ring" mode - overwrites oldest records when card is full

Field name	Units	Description
power_in_Avg	Vdc	Battery voltage
WindSpeed_sclr_Avg	m/s	Mean horizontal wind speed
WindSpeed_rslt_Avg	m/s	Mean wind vector magnitude
WindDir_rslt_Avg	degrees	Resultant mean wind direction
WindDir_sclr_Avg	degrees	Standard deviation of wind direction calculated using Campbell Scientific's wind speed weighted algorithm (not recommended for straight-line Gaussian dispersion models, but OK for variable-trajectory transport models ref)
Tmpr_Avg	ºC	Mean air temperature
RH_Avg	%	Mean relative humidity
Press_Avg	hPa	Mean barometric pressure
R_amt_Avg	mm	Mean rain amount
R_dur_Avg	sec	Mean rain duration
R_int_Avg	mm/hr	Mean rain intensity
WindSpeed_min_Avg	m/s	Mean minimum wind speed
WindSpeed_avg_Avg	m/s	Mean average wind speed
WindSpeed_max_Avg	m/s	Mean maximum wind speed
WindDir_min_Avg	degrees	^Mean minimum wind direction
WindDir_avg_Avg	degrees	^Mean average wind direction
WindDir_max_Avg	degrees	^Mean maximum wind direction

Notes:

• ^ value is dubious

Configuration Summary

I had a hard time locating a working copy of the manufacturer configuration tool and also was unable to get an instrument response using the service port and a serial terminal (RealTerm). Instead, use the CR1000's internal serial terminal to verify program settings. Hopefully it's already in SDI-12!

• Communications:
  • Address: 0
  • Protocol: SDI-12 continuous (aXU,M=R)
• Wind sensor:
  • Parameters: all of them (aXWU,R=1111110011111100)
  • Update interval: 60 seconds
  • Averaging time: 60 seconds
  • Min/max mode: traditional
  • Speed unit: m/s
  • Direction offset: 0 degrees
  • Sampling rate: 4 Hz
• Press/Tmpr/RH sensors:
  • Parameters: 1st (Pa), 2nd (Ta) and 4th (Ua) bits
  • Update interval: 60 seconds
  • Pressure unit: hPa (mbar)
  • Temperature unit: Celsius
• Precipitation sensor:
  • Parameters: first 6 (all but Rain peak and Hail peak)
  • Update interval: 60 seconds
  • Precip units: metric
  • Hail units: metric
  • Autosend mode: n/a for SDI-12
  • Counter reset: manual (default?)

Licensing

This software was developed by Patrick O'Keeffe for the Department of Animal Sciences at WSU. This software is released under the terms of The MIT License.

References

• Campbell Scientific. CRBasic Program Reference: WindVector. CR1000.Std.32.03.

• Campbell Scientific. WXT520 Weather Transmitter Instruction Manual. Retrieved 2019-04-01. Online: https://s.campbellsci.com/documents/us/manuals/wxt520.pdf

• O'Keeffe, Patrick. Long-term Trace Gas Flux Sampler. Retrieved 2019-04-01. Online: https://github.com/patricktokeeffe/smart-rea-sampler

• Vaisala Oyj. Vaisala Weather Transmitter WXT520 User's Guide. Retrieved 2019-04-01. Online: https://www.vaisala.com/sites/default/files/documents/M210906EN-C.pdf