DQRID : D941205.1
Start DateStart TimeEnd DateEnd Time Data Quality Metric
11/05/1994203011/15/19941530Suspect
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Subject:
SGP/TWR21x/C1 - Temperature Offset
DataStreams:sgp30twr21xC1.a1, sgp1twr21xC1.a0
Description:
On May 11, 1994 the site operators at the Central Facility had some difficulty performing 
an ice bath check on the 60 meter Tower PRTD (platinum resistance temperature device).  
After consulting with the mentor (me) they reperformed the check and appeared to obtain 
good results (an output of 0.00 degrees C). However, this required a change in the 
calibration ratio.

For the November 15, 1994 PRTD check I supplied a much more involved testing procedure 
than had been used previously.  The ice bath check on that day indicated that at zero 
degrees C, the PRTD output was -1.37 degrees C.  The calibration ratio was again adjusted, 
resulting in a ratio that is consistent with those determined in the checks previous to May 
1994.  The new ratio gave a temperature of -0.001 degrees C in the ice bath.

The ratio used between May 11 and November 15, 1994 (at the times indicated above) was too 
small, leading to an underestimation of temperature. Because of the technique used in 
the Campbell Data Logger for the determination of temperature from a PRTD, the Nov. 15 
initial ice bath reading of -1.37 degrees is essentially equivalent to an offset over the 
range of ambient air temperatures.  I confirmed this by measuring a range of temperature (0 
to 37 degrees C) with a 21X and a reference PRTD in our laboratory at ANL, simultaneously 
employing the two calibration ratios that we have used for the Tower PRTD after the past 
two calibration checks.

Users of Central Facility Tower temperature data for the period listed above should add 
1.37 degrees C to the data.

Since vapor pressure is calculated from the Tower temperature (degrees C) and relative 
humidity (in %) measurements, vapor pressures for the period listed are too small by about 
8% (the range is approximately 6% to 12%).  Vapor pressure should be recalculated by the 
user with the following equations:

   CALCULATE VAPOR PRESSURE (IN KPA) FROM TEMPERATURE (T) AND
   RELATIVE HUMIDITY (RH) USING THE COEFFICIENTS C0 THROUGH C6

      C0=6.107799961
      C1=4.436518521E-01
      C2=1.428945805E-02
      C3=2.650648471E-04
      C4=3.031240396E-06
      C5=2.034080948E-08
      C6=6.136820929E-11

      VAPOR PRESSURE=RH*(C0+C1*T+C2*T*T+C3*T*T*T+C4*T*T*T*T+
                       C5*T*T*T*T*T+C6*T*T*T*T*T*T)/1000.

Standard deviations of temperature and vapor pressure are probably very slightly 
underestimated, but the error in them cannot be quantified as we do not have the 1 second 
measurement data to recalculate them.  Use with caution.
Suggestions: 
Use data with caution
Measurements:sgp1twr21xC1.a0:
  • vap_pres
  • temp
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sgp30twr21xC1.a1:
  • sd_vap_pres
  • sd_temp
  • temp
  • vap_pres
more

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