Wide Band Instrumentation

Wide-bandwidth measurement equipment is used where both long and short time accuracy is required. Present sensing devices can be broken into two classes, namely those that function accurately over long time measurements and conversely those that indicate changes but are lacking long time stability. Pressure pickoffs and radars are examples that fall into the former class of devices while velocity pickoffs and accelerometers possess only short time accuracy. This paper presents a technique whereby both types of inputs are injected into a mixer whose output retains the good properties of each input while rejecting the inaccurate portions of the input data. The resultant output of the mixer is superior to either input, since it possesses both high and low frequency accuracy. A general method for solution of the mixer characteristic is given which indicates that complementary linear filters may be used to perform the mixing function. The system may be made dynamically exact, that is, the mixer has a unity transfer function and contributes no error in the absence of noise. The mixer parameters are chosen on the basis of minimizing the root mean square error in the output considering the noise inputs to the system. An illustrative example is given based on a Baro-Inertial Mixer using both pressure and inertial data to give accurate wide band vertical velocity as its output.