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N2O Flux Trailer Weather Station

Weather station (and communications package) for the WSU LAR N2O flux measurement support trailer.
Image of mounted sensors Image of logger enclosure

Hardware

Equipment inside a fiberglass enclosure on the trailer wall:

  • Battery-backed 12V power supply (PS100, Campbell Scientific)
  • Programmable datalogger (CR1000, Campbell Scientific)
  • Broadband modem (RV50, Sierra Wireless)
  • Rugged Ethernet switch (SW-504, Brainboxes)
  • Ethernet surge protector (ETH-SP, Ubiquiti Networks)
  • Wireless access point (Picostation M2, Ubiquiti Networks)

Sensors mounted on a short external mast:

The wireless access point can optionally be deployed outside the trailer on the external mast to obtain greater wireless coverage. Antennas for the broadband modem are permanently installed on a short mast at the nose of the trailer.

Wiring

Power System

All equipment listed above is powered from the battery-backed 12V power supply. If primary power is lost, the battery continues to operate the logger, sensors and communications network for up to several hours.

The communications equipment is battery-backed so network clients are still able to send email alarms during a power outage.

WXT510

The cable used does not match either vendor or manufacturer color conventions. Refer to this table exclusively for wiring the weather station:

Description Color M8 conn. pin CR1000 Ext. power supply
power input brown 2 12V -
power ground green 8 G -
cable shield bare - G -
SDI-12 data Tx yellow 7 C7 -
SDI-12 data Rx black 1 C7 -
SDI-12 ground white 3 G -
heater (+) blue 4 - 12V
heater (-) orange 6 - G
not used red 5 - -

QUANTUM (PAR) sensor

The QUANTUM (LI-190SA) sensor connects to the BNC connector of a 2290 (604Ω) millivolt adapter, and the millivolt adapter is measured differentially:

The millivolt adapter for LI-190SA series PAR sensor is measured with an inverted differential setup. The multiplier is also negative, which produces a positive value.

Description Color CR1000
Model 2290 Millivolt adapter, negative blue DF1 H
Model 2290 Millivolt adapter, positive green DF1 L
jumper to CR1000 DF 1L port green ⏚

Door switch

The magnetic reed switch door sensor is powered by the logger and connected to a control port.

Description CR1000
wire #1 5V
wire #2 C8

Operation

To deploy the sensors

The weather station and PAR sensor (with leveling mount) are attached to a short length of aluminum slotted angle framing. This entire assembly must be removed during travel, then installed and oriented at each new location.

To deploy the sensor mounting arm:

  1. Slip the mounting arm U-bolt over the instrument mast and secure loosely.
  2. Orient the mounting arm away from the equator (e.g. northward) to prevent shading the radiation sensor.

    The azimuth orientation of the weather station must be measured and specified in the logger program after installation. The default azimuth value (0) assumes the WXT510 is oriented towards True North.

  3. Tilt the mounting arm, as needed, to level the weather station.
  4. Secure the mounting arm U-bolt.
  5. Make final adjustments to the PAR sensor bracket to obtain a level position.
  6. Feed the PAR sensor cable through the wall port, into the logger enclosure, and attach to BNC jack of millivolt adapter.
  7. Feed the weather station data cable out of the logger enclosure, through the wall port, and attach to the weather station.
  8. Inside the logger enclosure, turn the power supply switch to ON.

To remove, perform the installation procedure in reverse.

It is not necessary or recommended to remove the weather station or PAR sensor and bracket from the mounting arm. The weather station cable and millivolt adapter for PAR sensor remain in the logger enclosure.

To update constants

Users can modify program constants to reflect sensor or location changes:

  • UTC_OFFSET - time offset relative to UTC, in hours (default: -8 = Pacific Standard Time)
  • WXT_AZIMUTH - orientation of the weather station w.r.t. True North, in degrees (default: 0 = True North)
  • PAR_MULT - unique sensor-specific calibration value, in µmol/(mV s m2) (default: 0 = no data) This value should be negative

To edit these values, users have several options:

  • Locally, using a keyboard display (not provided) to edit the ConstTable
  • Over the local area network, using LoggerLink to edit the public table Constants (recommended option)
  • Remotely (not described here), using LoggerNet Connect to edit the public table Constants

Refer to vendor documentation for logger setup details. When connected to the network locally (wired or wireless) the logger can be accessed via:

  • IP address: 192.168.13.11
  • Pakbus port: 6785

To view data

To view data, use any of the methods mentioned above (LoggerLink, etc) or visit the datalogger's IP address with a web browser. A default webpage allows visitors to explore recent records (screenshot below).

Default logger website

You must be connected to the trailer's local area network (wired or wireless) to view the logger webpage.

To download data

To download data, use logger support software (LoggerLink or LoggerNet) or use the Web API (details in CRBasic Editor Help).

For example, to download the last ~7.5 days (11,000 minutes) in TOA5 format (CSV+headers) using the Web API, visit:

http://192.168.13.11/?command=dataquery&uri=weather&format=toa5&mode=most-recent&p1=11000

You must be connected to the trailer's local area network (wired or wireless) to access the logger Web API.

Data Products

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

  • Base name: weather
  • Record interval: 1 minute
  • Number of records: up to 365 days
  • Fill-stop settings: "ring" mode - overwrites oldest records when memory fills
Field name Units Description
WindDir_min degrees Wind direction, minimum
WindDir_avg degrees Wind direction, average
WindDir_max degrees Wind direction, maximum
WindSpeed_min m/s Wind speed, minimum
WindSpeed_avg m/s Wind speed, average
WindSpeed_max m/s Wind speed, maximum
Tmpr degC Air temperature
RH percent Relative humidity
Press hPa Barometric pressure
Rain_amt mm Rain, amount
Rain_dur sec Rain, duration
Rain_int mm/hr Rain, intensity
Hail_amt mm Hail, amount
Hail_dur sec Hail, duration
Hail_int mm/hr Hail, intensity
HeaterTmpr degC Heating sensor temperature
HeaterVolts Vdc Heater input voltage1
PAR_density umol/(s m^2) Photosynthetic photon flux density (PPFD), approximately2
LoggerTmpr degC Logger enclosure temperature
PowerIn Vdc Power supply voltage3
DoorOpen Boolean Status of trailer door: 0 = closed, -1 = open4
ClockError msec Measured clock offset from UTC5
UTC_OFFSET hours Timestamp offset from UTC6
WXT_AZIMUTH degrees Azimuth correction applied to WXT510 wind direction values7
PAR_MULT umol/(mV s m^2) Calibration multiplier used with PAR sensor8

Footnotes:

  1. Available, not applied, heating voltage (should be same value as PowerIn). Refer to WXT510 user manual for heater operation details.
  2. Approximately because logger is configured for use with older (uncalibrated) LI-190SA series PAR sensors.
  3. Unregulated voltage from battery, typically >12.8 Vdc when a charging source (AC utility power) is available.
  4. Value will be NAN until sensor is installed.
  5. Network time protocol offset relative to 0.us.pool.ntp.org.
  6. Default value -8 = Pacific Standard Time (i.e. no adjustments made for Daylight Savings Time).
  7. Recorded wind direction min/avg/max values include this constant offset value
    (i.e. WindDiravg = (WindDiravg,measured) + WXT_AZIMUTH MOD 360).
  8. Value will be negative when used with LI-190SA series PAR sensors.

Configuration Summary

Use the Vaisala WXT Configuration Tool to modify settings as follows:

  • Device Settings
    • Enable heating
    • SDI-12 v1.3, continuous mode enabled
  • Message Settings
    • All wind messages
    • Barometric pressure, Air temperature and Relative humidity PTU messages
    • All precipitation messages, except Rain peak and Hail peak
    • Heating temp. and Heating voltage diagnostic/supervisor messages
  • Sensor Settings
    • Wind speed unit: m/s
    • Temperature unit: Celsius
    • Barometric pressure unit: hPa
    • Counter reset: Automatic
    • Rain unit: Metric
    • Auto report based on: Rain start/end
    • Direction correction: 0°
    • Averaging time for all sensors: 1 min
    • Update interval for all sensors: 1 min

Licensing

  • Original software contributions are licensed under The MIT License.
  • Documentation, including images, are licensed under CC-BY-SA-4.0 (Creative Commons Attribution-ShareAlike 4.0 International).
  • This work derived from Compost WXT520 Logger Program, which is also subject to The MIT License.

References