Incorrect readings for pressure sensor

ARM PROBLEM IDENTIFICATION FORM (PIF)

                            PIF No. P940105.1

Subject:  SGP/Ebbr - Incorrect readings for pressure sensor at E15

Submitted By:        David R. Cook
    Organization:    Argonne National Laboratory
    Date Submitted:  December 13, 1993

How may we contact you?
    e-mail:  cook@anler.er.anl.gov
    phone:   (708) 252-5840
    FAX:     (708) 252-9792

Submitter's Priority: 3
    [Critical-1   Very Important-2 Important-3 Inconvenient-4 Interesting-5]

Where was this Problem Identified:  DA
    [Site Data System-SDS      Experiment Center-EC]
    [Archive-A At              Field Instrument-FI ]
    [During Data Analyis-DA    Other- List Location]

Does this PIF result in a Software Change Request?  No
    Where:                     [ SDS,  EC, or  A ]

    Type:                      [Development-1 Problem-2  Enhancement-3]

    List Programs/Documents Affected:

    Configuration Identification:

Does problem impact data values or cause data loss?  Data values.
    which platform(s): EBBR, E15, Ringwood, OK

    Specify (or estimate) begin and end dates
          Begin Date   7/11/93
          End   Date  12/01/93   Time  1830 GMT

    Apparent cause of data loss, if known:

    SUGGESTED CAUSES:   Calibration Drift.
    [human error, component failure, temperature, lightning          ]
    [foreign matter, power loss, software failure,                   ]
    [communications failure, modification difficulites, specify other]


Problem Description/Change Description.

o For Instrument Problems ONLY,
        Identify MODE of Operation: Normal

o Give a brief explanation with details, attach examples and any supporting
  information.  This should include a description of analysis leading to
  identification of problem and, if known, recommended action.


Beginning July 11, 1993, the atmospheric pressure sensor at the E15
EBBR began indicating approximately 0.2 KPa lower than the colocated SMOS.
Between July 31 and August 22, 1993 the difference increased to between
0.25 and 0.30 KPa.  After August 22, the difference increased to 0.3 to
0.35 KPa and remained that way until December 1, 1993.  A comparison of the
EBBR pressure sensor with the portable standard on December 1, 1993
indicated that the EBBR sensor was 0.04 KPa higher than the standard; this
is excellent agreement considering that the uncertainty of the EBBR sensor
calibration is 0.15 KPa.  The consistent bias in EBBR pressure between July 11
and December 1 can be easily detected in comparisons with SMOS pressure data.
No EBBR data other than pressure was affected by the pressure problem;
calculations of specific heat at constant pressure (which includes the term
1/(p-vp)) times other terms (including p-.378*vp) result in no error to the
third decimal point at least in the resulting Bowen Ratio.  For example;
assume a common vapor pressure (vp) of 2.0 kPa, a common atmospheric pressure
of 97.0 kPa, and a corrupted atmospheric pressure of 96.65 kPa at the extreme.

       Uncorrupted                               Corrupted

(97.0-.378*2.0)/(97.0-2.0) = 1.0131   (96.65-.378*2.0)/(96.65-2.0) = 1.0131

   1.0131/1.0131 = 1.0000    There is no effect on the Bowen Ratio as a
                                       result of the corruption.

Therefore, no correction to the quantities calculated using pressure is
needed.

• Time offset from base_time(time_offset)
• Bottom air temperature(temp_air_bottom)
• Top vapor pressure(vapor_pressure_top)
• Top air temperature(temp_air_top)
• Bottom relative humidity (fractional)(rh_bottom_fraction)
• Wind speed arithmetic mean(wspd_arith_mean)
• Bottom vapor pressure(vapor_pressure_bottom)
• Wind direction vector mean standard deviation(wdir_vec_std)
• Top relative humidity (fractional)(rh_top_fraction)
• lon(lon)
• Reference temperature in enclosure(temp_reference)
• Bottom T/RH sensor temperature(temp_trh_bottom)
• Top T/RH sensor temperature(temp_trh_top)
• AEM position indicator(home_signal)
• Wind speed vector mean(wspd_vec_mean)
• -180.0 - +180.0(alt)
• Wind direction vector mean(wdir_vec_mean)
• Net radiation(net_radiation)
• North Latitude(lat)
• base time in epoch(base_time)
• Atmospheric pressure(atmos_pressure)

• lon(lon)
• Soil heat flow 2 (mV)(soil_heat_flow_2_mv)
• Atmospheric pressure (mV)(atmos_pressure_mv)
• Right relative humidity (mV)(rh_right_mv)
• Soil heat flow 5 (mV)(soil_heat_flow_5_mv)
• Soil temperature 5 (resistance ratio)(soil_temp_5_rr)
• Soil moisture 1 (resistance)(soil_moisture_1_r)
• Soil moisture 5 (resistance)(soil_moisture_5_r)
• Battery voltage(battery_voltage)
• Reference temperature in enclosure (resistance ratio)(temp_reference_rr)
• base time in epoch(base_time)
• Soil heat flow 3 (mV)(soil_heat_flow_3_mv)
• Net radiation (mV)(net_radiation_mv)
• Soil temperature 3 (resistance ratio)(soil_temp_3_rr)
• Soil moisture 4 (resistance)(soil_moisture_4_r)
• Left air temperature(temp_air_left)
• Soil temperature 4 (resistance ratio)(soil_temp_4_rr)
• Left relative humidity (mV)(rh_left_mv)
• Wind direction vector mean (mV)(wdir_vec_mean_mv)
• AEM position indicator(home_signal)
• Soil heat flow 1 (mV)(soil_heat_flow_1_mv)
• North Latitude(lat)
• Soil temperature 1 (resistance ratio)(soil_temp_1_rr)
• Right air temperature(temp_air_right)
• Left T/RH sensor temperature (resistance ratio)(temp_trh_left_rr)
• Soil moisture 3 (resistance)(soil_moisture_3_r)
• -180.0 - +180.0(alt)
• Soil heat flow 4 (mV)(soil_heat_flow_4_mv)
• Soil temperature 2 (resistance ratio)(soil_temp_2_rr)
• Right T/RH sensor temperature (resistance ratio)(temp_trh_right_rr)
• Wind speed arithmetic mean(wspd_arith_mean)
• Soil moisture 2 (resistance)(soil_moisture_2_r)
• Time offset from base_time(time_offset)

• Soil moisture 1, gravimetric(soil_moisture_1)
• Soil moisture 2, gravimetric(soil_moisture_2)
• Soil moisture 3, gravimetric(soil_moisture_3)
• Bottom air temperature(temp_air_bottom)
• Soil moisture 4, gravimetric(soil_moisture_4)
• Soil moisture 5, gravimetric(soil_moisture_5)
• Soil heat flow 4, corrected for soil moisture(corr_soil_heat_flow_4)
• Soil heat flow 3, corrected for soil moisture(corr_soil_heat_flow_3)
• Soil heat flow 2, corrected for soil moisture(corr_soil_heat_flow_2)
• Soil heat flow 1, corrected for soil moisture(corr_soil_heat_flow_1)
• -180.0 - +180.0(alt)
• Soil heat flow 5, corrected for soil moisture(corr_soil_heat_flow_5)
• Surface soil heat flux, average of fluxes 1-5(surface_soil_heat_flux_avg)
• Wind direction vector mean(wdir_vec_mean)
• Soil heat flow 4(soil_heat_flow_4)
• Soil heat flow 5(soil_heat_flow_5)
• Soil heat flow 2(soil_heat_flow_2)
• Soil heat flow 3(soil_heat_flow_3)
• Soil heat flow 1(soil_heat_flow_1)
• base time in epoch(base_time)
• Soil heat capacity 5(soil_heat_capacity_5)
• Soil heat capacity 4(soil_heat_capacity_4)
• Reference temperature in enclosure(temp_reference)
• AEM position indicator 0 to 15 mins(home_signal_15)
• North Latitude(lat)
• Time offset from base_time(time_offset)
• Bottom relative humidity (fractional)(rh_bottom_fraction)
• Wind speed arithmetic mean(wspd_arith_mean)
• Soil heat capacity 3(soil_heat_capacity_3)
• Soil heat capacity 2(soil_heat_capacity_2)
• Soil heat capacity 1(soil_heat_capacity_1)
• Bowen ratio(bowen_ratio)
• lon(lon)
• Wind direction vector mean standard deviation(wdir_vec_std)
• Surface latent heat flux(latent_heat_flux)
• Surface soil heat flux 5(surface_soil_heat_flux_5)
• Surface sensible heat flux(sensible_heat_flux)
• Surface soil heat flux 3(surface_soil_heat_flux_3)
• Surface soil heat flux 4(surface_soil_heat_flux_4)
• Atmospheric pressure(atmos_pressure)
• AEM position indicator 15 to 30 mins(home_signal_30)
• Top T/RH sensor temperature(temp_trh_top)
• Top vapor pressure(vapor_pressure_top)
• Surface soil heat flux 1(surface_soil_heat_flux_1)
• Surface soil heat flux 2(surface_soil_heat_flux_2)
• Net radiation(net_radiation)
• Change in energy storage 1, 0-5 cm soil layer(energy_storage_change_1)
• Half hour averaged soil temperature 4(soil_temp_4)
• Bottom vapor pressure(vapor_pressure_bottom)
• Change in energy storage 3, 0-5 cm soil layer(energy_storage_change_3)
• Soil temperature mean 3(soil_temp_3)
• Change in energy storage 2, 0-5 cm soil layer(energy_storage_change_2)
• Change in energy storage 5, 0-5 cm soil layer(energy_storage_change_5)
• Soil temperature 2(soil_temp_2)
• Change in energy storage 4, 0-5 cm soil layer(energy_storage_change_4)
• Soil temperature 1(soil_temp_1)
• Half hour averaged soil temperature 5(soil_temp_5)
• Bottom T/RH sensor temperature(temp_trh_bottom)
• Top relative humidity (fractional)(rh_top_fraction)
• Top air temperature(temp_air_top)
• Wind speed vector mean(wspd_vec_mean)