2.1 INTRODUCTION The Model 162 Boxcar Averager can be combined with one or two Model 163 or 164 Processor Modules to form a gated signal-recovery system of exceptional versatility. This system synchronously samples the input signal with an aperture that can be fixed at any point on, or slowly scanned across, the input signal. The signal passed through the aperture is applied to a variable time constant integrator, the output of which is the average of some number of repetitions of the input signal over the aperture duration. Because the average value of noise over a large number of repetitions is zero, an improvement in signal-to-noise ratio occurs, if the aperture is fixed on a single point of the input signal, the output of the Processor Module rises asymptotically towards the average value of the input signal at the sampled point. If the aperture is scanned across the input signal, the synchronous waveform is reproduced at the output at the scan rate. The Model 162 Mainframe contains most of the timing and control functions, as well as the output signal-processing circuitry. There is provision for supplying the gated-and-averaged signal from either channel to the mainframe output. Alternatively, one can select the difference between the two gated-and-averaged signals at the mainframe output. With the addition of optional signal-processing circuit cards, the Model 162 can provide an output consisting of the product, ratio, or log of the ratio of the two averager channel outputs. Use of the digital storage option ailows signals at extremely low repetition rates to be averaged. Prior to being made available at the Output connector, the mainframe output signal (ร smoothed by a iow-pass filter. The time constant of this filter is adjustable from 100 ^ts to 100 ร. Front-panel delay controls are provided that permit the aperture m each channel to be delayed independently from about 5% to 100% of the Delay Range, selectable in 1-2-5 sequence from .1 แร to 50 ms. Pushbutton switches give a choice of external, internal, or line triggering, and permit independent selection of manual or automatic scanning for each channel. The scan time, the time required to scan the aperture across 100% of the selected Delay Range, can be set to any value from 10 2 ร to 10s ร. Each of the Processor Module types provides a unique set of operating characteristics, allowing the input parameters of the Model 162 to be optimized to a very wide range of signal-recovery applications. The Model 163 Sampled Integrator module utilizes a Sampling Head to achieve aperture resolutions from 100 ps to 1 ns according to the Sampling Head selected. The input sensitivity is switch-selectable from 100 mV to 1 V full-scale. There is provision for selecting the number of samples averaged and for baseline sampling. This latter function provides automatic compensation for dc drift and the effects of baseline wander. The Model 164 Gated Integrator module offers a choice of aperture widths ranging from 10 ns to 5 ms. Pushbutton switches allow a choice of 50 Q or 1 Ml) input impedance, ac or dc coupled, and the choice of either linear or exponential averaging. Both the module gain and aperture duration can be trimmed to provide an exact match between modules if two Model 164’s are to be used in dual-channel operation. Both the Model 163 and the Model 164 provide output and aperture monitors, output reset switches, and an Overload lamp to indicate overload Both modules also provide a choice of the number of samples averaged. เท the Model 163, a single switch selects the number of samples of which the output is the average. เท the Model 164, the averaging Time Constant, together with the selected Aperture Duration, determines the number of samples of which the output is the average. The built-in flexibility of the Model 162 makes it suitable for handling almost any application involving the examination of repetitive signals. Use of the ratio option in dual-channel operation, for example, permits automatic source compensation for fluctuations in the excitation power of pulsed lasers and transducers. Dual-channel operation also permits single-unit instrumentation in complex experiments such as time-shared dual-beam spectroscopy. As a single-channel or dual-channei gated averager, the Model 162 is ideally suited to such applications as time of flight studies, plasma physics research, fluorescence and phosphorescence decay, non-destructive testing, and turbulence studies in fluid mechanics. The use of plug-in signal channel modules and plug-in optional signal-processing function cards, when combined with its many built-in operating features, makes the Model 162 Boxcar Averager the most versatile gated signal averager available.