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. |