(2) Launcher 



Insulation Leakage 



(3) Probe 



Wire Resistance Unbalance 

 Wire Insulation Leakage 

 Thermistor Offset/Slope 

 Thermistor Insulation Leakage 



Installation of an A2A test canister in the launcher provides an overall system test for (1) 

 and (2) above. If the results of this test indicate that no setting of the zero and full-scale 

 adjustments for-l.l°±.l° and 34.4°C±.1°, respectively, result in a 16.7°±.]°C mid-scale 

 reading, then a 100 VDC high pot check of launcher leakage resistance (normally done on 

 a monthly basis) would be in order to determine a probable launcher leakage resistance 

 condition of considerably less than lOOMfi. Alternatively, testing with an A4 XBT test 

 box will also indicate the presence of excessive launcher leakage. 



Many times in the report the phrase, "accuracy criteria," in regard to XBT 

 temperature is used without specific reference to actual value. It is assumed from the 

 analysis on page 19, Vol. I of Mr. Anderson's report that ±.24°C (two standard deviations of 

 assumed value of ±.12°) is meant.* Sippican specifies the system with a stated worst case 

 temperature accuracy of ±.2°C (±.1°C for the probe and ±.1°C for a properly maintained 

 and calibrated recorder). Such caUbration will provide a read-out within ±.1°C at -1 .1°C, 

 +16.7°C and +34.4°C when checked with an A2A test canister. Because it is possible that 

 a shift in gain can occur that will affect high temperature readings twice as much as mid- 

 scale readings, and very Httle at low temperatures, the practice of using the mid-scale 

 calibration value as a correction is questionable. It's better than no correction but obviously 

 more "chancey" than recalibrating the system. For a simple zero offset error, the practice 

 is reasonably acceptable since it applies almost equally across the total temperature span. 

 ("Almost" because of the chart nonlinear temperature compensation used to correct for the 

 thermistor-series resistor "S" curve nonlinearity of .8°C at about .8°C and 24. °C). 



The procedure Sippican would use for those applications requiring retention of full 

 available system accuracy is to calibrate with an A2A test canister whenever (1) a new roll 

 of chart paper is installed, (2) at four-hour intervals during continuing drops, and (3) when- 

 ever the 2-second, mid-scale calibrate trace exceeds ±.1° from 16.7°C. In addition, a once 

 per day check using an A4 XBT test box provides a quick indication of incipient launcher 

 leakage before it becomes severe enough to affect system accuracy.** 



Assuming a correctly-maintained and adjusted launcher-recorder system, then a 

 series of probe drops will reflect probe wire/thermistor problems as follows: 



• Wire Resistance Unbalance 



May be either up or down scale error depending on which lead has higher 

 resistance; will have more noticeable effect at higher temperatures where thermistor 



*See author's note A. 

 **See author's note B. 



135 



