NIS Calibration Report #15

Jim Bell, Andy Switala; 2/23/96


NIS Temperature Measurements


This document provides a summary of the various NIS temperatures that are monitored during flight, how the telemetry and packet data are converted into actual temperatures, and how accurate these temperatures are estimated to be.


The original conversion between counts and temperatures was provided in Hugo Darlington's memo S1I-95-072a of July 20, 1995. Using those conversion equations, it was found that there was a large and unexplained discrepancy between the Ge and InGaAs temperatures for many of the OCF tests. The recommendation was that we revisit this issue during the NIS TV tests at GSFC. This was done by using some well-calibrated thermocouples during the TV tests to record the "actual" temperatures.

Scott has provided me with 4 pages of data obtained on November 5, 6, 8, and 14, 1995 during NIS TV testing. The data consist of log sheets onto which the thermocouple temperature and corresponding Ge and InGaAs counts were recorded. These data allow us to produce the figure attached to the end of this report, plotting Calculated Ge and InGaAs temperatures vs. the temperatures measured by the thermocouples.

The plot reveals several things. First, the difference between the "actual" temperature and the calculated temperature for Ge appears to differ by a roughly constant offset of about 8 degrees C. Second, the difference between "actual" and calculated temperatures for InGaAs is higher, at about 13 degrees C. Third, there is more noise in the InGaAs temperature data compared to Ge, but this may just reflect the influence of one bad measurement.

Jeff, Keith, Hugo, and Scott: I would like to get your feedback on this plot so that we can resolve this issue. Some specific questions that we should address:

(1) Can one of you provide a concise description of where the thermocouples were located and how well they were calibrated?

(2) Are there any more data from TV that can be used to assess the NIS temperature calibration besides the data from these 4 days?

(3) How much does this matter? That is, how important do YOU see it that we know the _absolute_ temperature of NIS to within a few degrees as opposed to simply using Hugo's equations to provide a _relative_ temperature calibration that can be used with pre-flight OCF and TV data?

I would appreciate all of your thoughts on these questions before we try to proceed further.

Also, after launch Jeff indicated that the NIS temperatures appeared to be falling nominally as predicted. What temperature is this that is being measured?


Figure 1:

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Last Modified by Jim Bell on 29 February 1996.
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