Description: | On June 14 through 17, 1995 the 60 meter temperature sensor output drifted low.
On September 18, 1995 at 1828 GMT I observed the temperature to be 18.42 degrees C. At
1838 I discovered that the 100 ohm resistor connected to the CR21X was not making good
contact. Once good contact was made, the temperature indicated 27.38 degrees C. The
difference of nine degrees is consistent with the difference between the Sonde and tower (for
similar temperature conditions) since June 17. The calibration of the sensor for that
period is incorrect. It may be possible to determine a correction to the 60 meter
temperature for that period from the imformation that I gathered while at the SGP CART Site on
September 18 and 19; I will write an addendum to this DQR once I determine if this is possible.
Temperature data for 1828 through 1845 GMT on September 18 is incorrect because I was
fiddling with the CR21X connections during that period.
On September 19 the 60 meter tower carriages were lowered for RH probe checks and
replacement and for an ice bath calibration of the PRTD. All temperature data between 1407 GMT
and 1715 GMT is incorrect for September 19 as a consequence of the carriages being down.
An ambient air check of the PRTD indicated 22.7 degrees, with the HMI31 indicating 21.4
and the psychron (an ANL instrument that indicates dry and wet bulb temperatures within 0.1
degrees when both are dry) 21.6 degrees. The greater PRTD temperature was expected as
the calibration ratio determined for the ice bath during the last calibration (May 19,
1995) was larger than expected. Apparently, poor contact of the 100 ohm resistor began at
that point, although it worsened, probably from tower wind vibration, in mid June. The
evidence at the time of the May 19 calibration seemed to be that the ratio was appropriate.
I performed an ice bath check and ambient comparisons versus the HMI31 and psychron with
the help of Chris Martin of site operations. As a result, the multiplier used in the
CR21X was changed from 1.0141 to 1.0039. The latter is much more like previous correct
determinations of 1.0053, 1.005, and 1.0032 (not in chronological order). Ambient checks with
the carriage down then indicated 22.3 degrees for the PRTD, 22.4 for the psychron, and
22.0 for the HMI31.
Correct Temperature, Relative Humidity, and Vapor Pressure data began after 1715 GMT on
September 19, after the carriages returned to their proper positions. |