93 - 



the transducer to establish a zero-differential tare value 

 invalidates any calculations of instrument tilt or ambent temperature 

 using dPA signals (Section IV. C. A). 



6. Temperature Effect 



All transducers are temperature sensitive to some degree. 

 The thermal sensitivity specifications of the DPG's Setra absolute 

 and differential pressure transducers are less than +0.027. FS/°F and 

 +0.037. FS/°F thermal zero shift with thermal coefficients of 

 sensitivity of less than +0,015°/ FS/°F and +0.027. FS/°F respectively. 

 The transducer and sensor systems in the DPG are slightly more or 

 less sensitive than the factory specifications because of their fluid 

 back-fill. As the DPG environment changes temperature the 

 back-filling gin expands or contracts. Moreover, a temperature 

 change induces a slight differential pressure across the differential 

 transducers because of the greater volume of fluid in the (longer) 

 arm sensors. Since the volumetric expansion of a fluid is linearly 

 propOf'^ional to the change in temperature and initial volume of fluid, 

 the expanded volume in the arm sensors will be four times that of the 

 center sensors, (since the arm tubing is four times the length of the 

 center tubing.) But since temperature changes under twenty feet of 

 ocean water are typically small and of low frequency, it is assumed 

 that any thermal transducer drift during a sampling interval will be 

 interpreted as a very long period wave or as a mean which changes 



