EPHIN Rates v Sensor Temperature (5EPHINT) 2013-02-10 to 2013-10-05

As we continue to relax the Mission Planning Guideline that covers the EPHIN Thermal Limit, we need to trend the EPHIN performance to monitor for unexpected changes in performance. The plots here show the trends observed during the period from 2013-02-10 to 2013-10-05. During this interval the TEPHIN planning limit started at 144 degF and was raised to 147 degF on 2013-03-21 and to 151 degF on 2013-07-11.

EPHIN data were selected for times outside the rad-zone, during the nominally scheduled time with RadMon enabled. Data from times of elevated solar activity have not been excluded.

The behavior of the data from the time interval covered here displays trends expected from previous intervals: (2011-07-17 to 2012-09-01) and (2012-09-01 to 2013-02-09). Detectors D and E now show an upturn in rates at high temperatures similar to what has previously been seen in detector C. These increaing rates cause an upturn in the E1300 coincidence channel rate.

EPHIN E150 Coincidence Rate

The E150 rate shows more of the anomalous behavior first observed during the Normal-Sun time of the CTU TLM-Processor reset. This anomalous behavior led to halting the use of the E150 channel for safing within RadMon.

EPHIN E150 rate vs 5EPHINT
Figure 1: EPHIN E150 coincidence channel rate vs EPHIN sensor temperature The sensor temperature values have a small, uniformly-distributed random valued added for display purposes.

E1300 Rate

The E1300 rates show drops associated with higher EPHIN sensor temperatures. The decrease in rate with higher temperature is due to a decrease in detector C and D sensitivity as the temperature increases. There is now an upturn in the E1300 rate at temperatures greater than ~65 degC due to accidental coincidences among the C and D detectors at their higher rates. These accidental coincidences are approaching the RadMon trigger threshold.

E1300 rate vs 5EPHINT
Figure 2: EPHIN E1300 coincidence channel rate vs EPHIN sensor temperature, similar to figure 1. The red hoizontal line is drawn at the RadMon trigger threshold.

Detector B0 (Center Segment)

The detector B0 rate increases are similar to the increases in the E150 rate as expected given that the B0 signal is the dominant component of the E150 coincidence channel. The anomalous rates in the B0 detector are what create the anomalous E150 rates.

Detector B0 rate vs 5EPHINT
Figure 3: EPHIN detector B0 rate vs EPHIN sensor temperature, similar to figure 1.

Detector C

The detector C rate decreases with increasing sensor temperature above roughly 43 degrees C. This behavior is the same as observed prior to setting detector A failure-mode on. The decrease in rate implies a decreased sensitivity to particles and is due to a lower voltage across the detector. The upturn in the rate above 55.5 degC (similar to detector B0) is likely due to leakage current.
Detector C rate vs 5EPHINT
Figure 4: EPHIN detector C rate vs EPHIN sensor temperature, similar to figure 1.

Detector D

The detector D rate decreases with increasing sensor temperature above roughly 50 degrees C, somewhat higher than detector C. As with detector C, the decrease in rates implies a decreased sensitivity to particles. The higher temperature of the on-set of the decrease is consistent with the different detector thickness. The rate increases above 64 degrees C similar to that observed in detector C; again the higher temperature for the onset can is due to the greater detector thickness.
Detector D rate vs 5EPHINT
Figure 4: EPHIN detector D rate vs EPHIN sensor temperature, similar to figure 1.

Detector E

The detector E rate decreases with increasing sensor temperature above roughly 50 degrees C and shows a sharp increas above 64 degress C, similar to detector D.
Detector E rate vs 5EPHINT
Figure 4: EPHIN detector E rate vs EPHIN sensor temperature, similar to figure 1.

Detector F

The detector F rate shows an increase as the rate exceeds roughly 53 degrees C. This may be due to increasing noise that would be reflected in a higher leakage current. Unfortunately, the ceiling on the telemetry reading for the leakage current has been reached at 48 degrees C.
Detector F rate vs 5EPHINT
Figure 4: EPHIN detector F rate vs EPHIN sensor temperature, similar to figure 1.
Mike Juda
Last modified: Tue Oct 8 09:17:28 EDT 2013