PREAMPLIFIERS, AMPLIFIERS

Besides evident failures and easy-to-appreclate kinds of malfunctioning, analog instruments may present some performance degradations whose detection may imply application of sophisticated tests. The last point represents the peculiar difference in troubleshooting between analog and digital instruments. 

The steps of intervention required to eliminate a trouble in analog Instrumentation are described in Table 6.1. 

Steps a) and b) are carried out in the same way regardless of the nature of the faulty instruments test c) has to be tailored to the actual nature of the faulty Instrument, though requiring a common testing structure which exists in most laboratories while d) may require even purposely developed Instrumentation. 

The correct way of carrying out steps a) to c) will now be discussed, while test d) will be described with reference to the specific Instruments that will be considered afterwards. 

The analog instrument you will be required to repair or to bring back to operate within the manufacturer s specification can be either  

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The molecular sensitivities of the first and second generations of the bDNA assays were limited by nonspecific hybridization between the amplification probes and other nucleic acids. Short regions of hybridization between any of the probes constituting the amplification system, (preamplifier, amplifier, and labeled probe) and any nontarget nucleic acid sequence leads to amplification of the background signal. Capture probes, capture extenders, and sample nucleic acid are all sources of this background hybridization (Collins et al 1997). 

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. 

The preamplifier/amplifier amplifies the voltage pulse to a usable size. 

The gamma ray scintillation spectrometer (Fig. 1) consisted of two single channel analyzers coupled to a common sodium iodide well detector, preamplifier, amplifier and scalers. By setting each analyzer for the appropriate energy the two isotopes were determined. 

Dead time, or resolving time, of a counting system is defined as the minimum time that can elapse between the arrival of two successive particles at the detector and the recording of two distinct pulses. The components of dead time consist of the time it takes for the formation of the pulse in the detector itself and for the processing of the detector signal through the preamplifier-amplifi-er-discriminator-scaler (or preamplifier-amplifier-MCA). With modern electronics, the longest component of dead time is that of the detector, and for this... 

The most important elements affecting the energy resolution of a radiation detection system are the three statistical factors mentioned above in relation to the width F. It is worth repeating that in energy measurements it is the energy resolution of the counting system (detector-preamplifier-amplifier) that is the important quantity and not the energy resolution of just the detector. 

The detector described above is of the continuous type. Position-sensitive detectors of the discrete type have also been developed. They consist of individual semiconductor elements all placed on the same base material, with each element connected to its own preamplifier-amplifier system. Two-dimensional detectors of the continuous type as well as of the discrete type have... 

A basic counting system for activation analysis consists of a detector [Ge or Si(Li)], electronics (i.e., preamplifier, amplifier), and a multichannel analyzer (MCA). Modern MCAs do much more than record the data. They are minicomputers or are connected to computers that store and analyze the recorded data. Examples are the ADCAM architecture offered by EG G ORTEC and the Genie-ESP VAX-based Data Acquistion and Analysis System offered by Canberra. 

Additional mode converters. These convert current into voltage, step functions into pulses, voltage into a binary number, etc. They include preamplifiers, amplifiers, discriminators, and analog-to-digital converters (ADCs). 

Different data acquisition systems can be applied. One possibility is to send the output signal from the electron multiplier to a fast pulse preamplifier-amplifier/discriminator and a multichannel scalar. 

Reactor Gold sample Indium sample BF3 detector Preamplifier Amplifier MPC counter... 

Preamplifier, amplifier, scaler (multipurpose counter), high and voltage supply. Optional oscilloscope. 

Preamplifiers, Amplifiers Scalers, Timers, Ratemeters Multichannel Analyzers Dedicated Instruments Tools, Instruments, Accessories, Components, Skills Interfaces Power Supplies Preventive Maintenance... 

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