Single Channel Analyzer Operation

The preamplifier amplifies the voltage pulse. Further amplification is obtained by sending the signal through an amplifier circuit (typically about 10 volts maximum). The pulse size is then determined by a single channel analyzer. Figure 10 shows the operation of a single channel analyzer. 

By using a discriminator,the scaler can be set to read only the larger pulses produced by the neutron. A discriminator is basically a single channel analyzer with only one setting. Figure 12 illustrates the operation of a discriminator. 

There are two dials on the front panel of the unit. One is marked E, for energr, or LLD, for lower-level dial the other is marked AE or ULD/AE, for upper-level dial/AE. There is also a two-position switch with INT (integral) and DIFF (differential) positions. In the INT position, only the E dial operates, and the unit functions as a discriminator. In the DIFF position, both E and AE operate, and the unit is then a single-channel analyzer. 

The single-channel analyzer (switch position DIFF). Both E and AE dials operate. Only pulses with heights between E and E + AE are counted (Fig. 

Multi-channel Analyzers. The first widely adopted multi-channel system was the SMA 12/60 (jequential /Multiple analyzer) introduced by Technicon in 1967. Built on the continuous-flow principle, it is similar in operation to the single-channel analyzer shown in Figure 24.12, but with the sample split into 12 channels. This generates 12 results sequentially on each sample at the rate of 60 samples, calibrators, and controls per hour. The 12/60 helped to establish the role of the screening battery or profile in diagnostic medicine. 

Fig. 5. Schematic of a Mossbauer spectrometer working in multiscaler operating mode abreviations A - multi-channel analyzer, G - square-wave generator, J - integrator, > - amplifier D - differentiator, M - movement system, S - source, A - absorbent, D - detector and S-A single channel analyzer, respectively...

Figure 4.47 Definition of deadtimes in the single-channel analyzer system with the pulse-height selector operating in the integral mode. (Reprinted by courtesy of EG G ORTEC.)...

We have optimized an eight-way MUX coupled to a TOFMS analyzer to carry out eight-channel parallel LC/UV/MS analysis of combinatorial libraries14 in the past 2 years. This system has not only provided the capacity needed for library analysis, but also enabled simultaneous evaluation of experimental parameters to expedite the method development process. In this chapter, we discuss the optimization of this system and present a high-throughput protocol for combinatorial library analysis. We also compare the eight-channel parallel LC/UV/MS system to a conventional single channel LC/UV/MS system in terms of performance and operation. 

Beta Scientific make three analyzers, the 4200, the 4201 and the 4203. These instruments were designed for unattended and fully automatic operation, complete analyses in less than 10 minutes, cost effectiveness and an ASCII, R232 interface for computer or LIMS connection [196]. The model 4200 is a single channel instrument with no R232 interface and manual calibration the model 4201 also includes an R232 interface, and the moel 4203 is a three channel version without sample preparation but with an R232 interface. The model 4210 is a th station sample preparation unit, a required accessory for model 4203. 

The voltage pulse produced by the TAC is fed to the multichannel analyzer (MCA), and is stored in a specific channel according to its amplitude, and hence time, post-excitation. The probability of a single photon event being counted is high soon after excitation and decreases with time. Repetitive operation of the TAC produces a probability histogram for the detection of fluorescence photons, which is identical to the fluorescence decay curve. 

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