SECTION 6.0 



ERRORS INTRODUCED BY CALIBRATION AND 

 RECALIBRATION OF THE BATHYTHERMOGRAPH 



6.1. General 



The calibration tests to date are the only tests that a Bathythermograph re- 

 ceives which can in any way check its accuracy and reliability. These calibration 

 tests are in general too infrequent and not of sufficient extent. Calibration tests 

 under idealized conditions and employing secondary temperature and depth meas- 

 uring instruments can provide some reliable indications of the possible sources of 

 errors of the Bathythermograph, these being determined experimentally independ- 

 ent of ocean variability. 



At the same time it should be noted that calibration techniques are also a pos- 

 sible source for the introduction of errors. These errors would originate primarily 

 from failure to determine whether or not the Bathythermograph has linear charac- 

 teristics. In particular there is evidence to show that the pressure elements are not 

 linear with respect to depth measurements. These conditions can be determined ex- 

 perimentally in the calibration procedures, however. 



The present techniques for calibration and recalibration procedures are satisfac- 

 tory as far as they go, but do not cover sufficient grounds. Briefly the problems may 

 may be summarized as follows : 



a. No tests are run before Bathythermograph is repaired. 



b. Tests are not conducted often enough on each Bathythermograph unit. 



c. Test log and history of repair of Bathythermograph are not kept at all or is 

 incomplete. 



d. There is no uniformity between test stations. 



e. The capacity of the testing stations is too small for the amount of Bathy- 

 thermographs which must be calibrated. 



f. The tests are not complete enough. 



(1) Do not account for hysteresis. 



(2) No rate of response tests. 



(3) No stability tests (run through a second time to see if same as first 

 time) (initial fatigue of new parts). 



(4) No smoothness tests are run (change of temperature with change of 

 depth under idealized conditions to test smoothness of response). 



6.1.1. Pre-Repair Tests 



There are at present no tests conducted (except in certain special cases) to 

 determine how much in error an instrument is before the instrument is cleaned, re- 

 paired, and put into shape. Such a pre-repair test would give valuable information 

 which would aid in evaluating the reliability of the data taken by the instrument, 

 and the corrective factors to be applied when indicated, particularly if a BT log 

 was kept. 



It is true that at present the majority of instruments sent in for recalibration 

 are completely inoperative to begin with. This condition lies partly with the length of 

 time an instrument is in use before it is sent back for recalibration. 



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