86 



acrylic housing and not upon the fluid. (intuitively, one would 



expect this to happen even in the ideal case of force applied by the 



dynamic water column — if the exposed elastomer area was so small 



that it could not deflect.) 



A slightly more sophisticated calibration system was then 

 designed. The system, as drawn in Figure V-3, consists of two 

 pressure chambers which secure around each isolation diaphragm of a 

 differential transducer, (only one is used with the absolute 

 transducer) . Each chamber is equipped with its own pressure 

 transducer and a bicycle tire valve stem. The chambers are connected 

 by tubing with a valve in the center to isolate, bleed, or allow the 

 chambers to communicate with one another. The chambers are built of 

 short steel cylinders with a plate welded on one end. Each chamber 

 is secured to a sensor diaphragm with a short length of motorcycle 

 tire inner tube that is glued to the chamber and hose-clamped to the 

 isolation diaphragm housing. The system is pressured with a bicycle 

 tire pump and the pressure sensed in each chamber and by the DPG 

 transducer is reported on a multi-channel strip chart. The DPG 

 transducers' response was interfaced with the strip chart using a 

 short "bench cable" that mated with the instrumentation connector 

 located within the DPG transducer stack. 



