ORTEC 420 - Optimal Operating Conditions

4-3
4.4 Typical Operating Conditions
The realization of both optimum timing and optimum energy resolution are mutu
ally exclusive when using the crossover pickofF method of timing; however, a
satisfactory compromise of timing and resolution is usually not difficult to obtain.
Optimum timing is realized with wide bandwidth capabilities in the linear ampli
fier, resulting in fast rise and fall times. Optimum energy resolution is realized
with narrow bandwidth so that the bypass of the noise spectrum can be selectively
chosen at a particular location in the frequency spectrum.
The method of compromise is illustrated with reference to the model 410
Amplifier when used in conjunction with the Model 420 Timing Single
Channel Analyzer. To optimize timing, the Model 410 would be operated: 1) with
a minimum of integration and double delay line differentiation; or 2) in the double
RC shaping mode with the integration and differentiation time constants set on
0.1 microsecond. The optimization of timing would be at the expense of energy
resolution. If it is desired to optimize the energy resolution, the Model 410 should
be operated: 1) with an integration time constant of 1 or 2 microseconds and
double delay line differentiation; or 2) in the double RC shaping mode with the
integration and differentiation time constants set at 1 or 2 microseconds. In the
latter case, it is observed that the rate of change of voltage when the linear
amplifier output crosses through zero is very much less than in the former case.
With the lower rote of change, the noise modulation of the linear amplifier output
signal causes a larger time jitter of the timing output signal. In the former cose,
the rote of change of voltage with respect to time is quite high and the jitter in
the timing output due to linear amplifier noise modulation is quite small.
Jj^