5.3.4. Change in Lag Conditions 



In some rare cases hysteresis can result from a change in lag conditions. This is 

 brought about for example by allowing the Bathythermograph to plow into the 

 mud. When the Bathythermograph comes up again it is covered with mud, thus in- 

 sulating the thermal element. The response to temperature changes is thereby de- 

 layed and a curve displacement results. Such a displacement may result also from 

 sudden shock which will change the location of the pen arm. This type of displace- 

 ment is usually a permanent one, however. 



5.4. Response Characteristics 



5.4.1. Response Hysteresis 



Response hysteresis has already been discussed in the above sections. 



5.4.2. Response at Initial Depth 



There is good cause to believe that the Bathythermograph may not respond with 

 respect to its pressure sensitive element in the initial depths.This is borne out by 

 experiments which compare the Bathythermograph trace to traces made by ther- 

 mister beads. 



The lack of this response of the pressure bellows in the initial depths followed 

 by a sudden response of this element to the conditions would result in a straight or 

 isothermal line from zero feet to the point at which the bellows element responded. 

 The temperature registered for the zero depth value therefore would be that actually 

 found at the depth at which the Bathythermograph responded, say 10 feet. This is 

 vitally important when considering the desirability of checking the absolute value 

 of the zero depth reading of the instrument with an independent measurement such 

 as the bucket temperature. If the Bathythermograph is not registering an actual 

 zero depth value but rather a line representing the 10 foot value, such comparisons 

 can be in great error. This is further discussed under temperature correction ap- 

 plications. 



5.4.3. Mechanical Hesitation 



In just the same manner as the Bathythermograph is believed to hesitate in the 

 initial depths before responding, so it is quite possible for the Bathythermograph to 

 hesitate all along its path producing a series of minor wiggles in the Bathythermo- 

 graph trace. These minor wiggles, if they are due to mechanical hesitation, are 

 consequently a source of error. 



There are no experimental data to support the presence and, if so, the magnitude 

 of these mechanical hesitations. It can only be stated at this point therefore that 

 such mechanical hesitations can exist as a possible source of error and should be 

 considered whenever wiggles in a trace become an important factor in analysis of 

 the data. 



These mechanical hesitations could easily look like true ocean variability, or 

 thermal microstructure. Some data suggest that the Bathythermograph does not 

 reproduce thermal microstructure while other data indicates very fine wiggles equi- 

 valent to thermal microstructure. This indicates that a resolution of these errors be 

 made by further research. 



5.5. Bathythermograph Sets 



All of the conditions discussed above are representative of possible sources of 

 errors which will reflect in the reproducibility and accuracy of the instrument in its 



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