Pore is generally referred to as a "calibrate step." If the unbalance is such that the galvanometer deflection is in the direction designated as positive, it is known as "cal plus"; if the deflection is in the opposite one ae nf): of light to be deflected from a zero position on the moving sheet of photographic paper. If the signal is too strong, it may be attenuated by changing the attenuation switch from position 1 to position 3. The calibration device is used as a rapid check on the sensitivity of the system. It does not aid in determining the relationship between gage output and the measured function. The calibration device provides a known bridge unbalance by putting a resistance in parallei with one of the arms of the bridge which in turn produces a certain galvanometer de~ flection which is a measure of the over~all sensitivity. This operation eve the galvanometer in the oscillograph which in turn would cause a beam MBAS OLS ep TEES SON ase a signal that would be transmitted through the bridge balancing unit to LOEoe e ne en nmr ype ~es woe tere ge ~ 2 ee A photosensitive device manufactured by Edgerton, Germeshausen & Grier, Inc., and known as a "blue box" was employed to provide a time reference on the oscillograph record. The device is actuated by bomb lighting and, hence, can be used to indicate burst time. The unit was located in the bottom of the fuselage aft of the rear crew compartment. 2.3.4.2 High Frecuency Pressure Recorder £ The High Frequency Pressure Recorder, Type FPR~3, was manufac= tured by Cook Research Laboratories. In conjuction with the crystal microphone pressure transducer explained in paragraph 2.3.1.1, the system was capable of measuring recording pressure transients as a function of time. Basically, the system consisted of a pressure transducer that supplied an electrical signal to the horizontal deflection plates of an oscilloscope causing a beam deflection recorded by a continuous strip camera, The oscilloscope, a modified Type 279 Du Mont Dual-Seam Oscilloscope, had an amplifier for each of two beams. The gain of these amplifiers was so adjusted that for one amplifier a 2 psi input would cause fullscale deflection while the other amplifier required 6 psi on the crystal to produce full-scale deflection. The system was calibrated in the air by introducing a 400 cycle square wave signal of the proper magnitude to simulate the transducer output corresponding to a 2 psi pressure differ ential, 2.3.5 Photography Motion picture photography was employed to measure the deflection of various components as a result of blast loading. Displacements were to be measured with respect to the part of the aircraft upon which the camera was mounted. The cameras, a total of five, were mounted as a unit atop the fuselage between the wines at fuselage station number 785, The wing tips, nose, and empennage could be viewed from this location. io we placed on the wings ard aft fuselage as reference markers Fig. 2.5). The cameras comprised three 16 =m SSAP cameras and two, Model H, 35 ma Camera-Flex cameras. The GSAP carceras asd Camera-Flex cameras were Operated at speeds of 64 frames per second and 128 frames per second, 29 -r direction, it is known as "cal minus."