Thermometer Calibration Data

The temperature sensor used for the Webster, Texas temperature history plots has been calibrated one time. This was achieved by a friend, Chuck Campbell, on June 2, 1997 by comparing the output of the outdoor probe to that of an Omega DP80 platinum temperature probe. Both sensors were placed in beakers of water at various temperatures between 32 and 109 deg F. A total of 50 comparisons were made. The next plot shows the time history of this calibration. The experiment shows the same basic offset whether the water was being cooled or heated implying the probes were responding quickly enough to accurately measure the changing temperature. The data points that were't included in the calibration were mostly taken soon after a large change in the water temperature. It was feared the sensor may not have reached equilibrium so this data was ignored.

Temperature calibration time history (3351 Bytes)

The next plot shows the data replotted vs. the output of the Omega sensor which was assumed to give exact measurements. The probe appears to differ from the more accurate sensor by a nearly constant offset of 1.65 deg F. This is well within the advertised tolerance of +/-2 deg F.

Outdoor temperature calibration (4323 Bytes)
The next plot shows the calibration of the indoor sensor. For this calibration, the outdoor probe was placed in contact with the indoor probe and various air temperatures were measured. Most of the readings were at room temperature. A few points were taking using the exhaust from a computer monitor as a heat source and the coldest point was obtained in a refrigerator. The high temperature points were thrown out since the localized heat from the monitor was found to be conducted into the probes unevenly. Once the readings were taken, the values read for the outdoor probe were calibrated using the 1.65 deg F offset derived above. The resulting value was used to calibrate the indoor probe. The resulting offset from the "correct" value was 0.72 deg F.

Indoor temperature calibration (4130 Bytes)
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