Scaler signals

The detector signal is conditioned through a single channel pulse height analyzer whose output pulses are fed to a scaler-timer in the single crystal controller. 

Under normal operating conditions the system is designed to acquire data from the peripherals at times determined by the preset time on the scaler rate meter. When the rate meter finishes its time interval the interface is signaled to acquire the stored... 

The discriminator produces an output pulse with a fixed shape (generally square) and size when the input signal crosses a reference. Discriminators usually have multiple identical output signals. The logic pulses can be sent to a scaler that simply counts the number of pulses, to a count rate meter to monitor radiation rates or doses, and to a time-to-amplitude converter (TAC) to measure the relative times of arrival of two or more logic signals. 

Figure 4. Decay of CF2C102 radicals in the reaction, CF2C102 + N02 =s CF2-C102N02. The peroxy radical was monitored by the signal at m/z = 82 (CF202) +, which was accumulated for 4748 flashes. Each channel of the multichannel scaler represents a time increment of 0.1952 ms.

A small portion of the mixture leaks out of a pinhole and is formed into a beam (Fig. 2.14). The radicals are ionized by light from a halogen, hydrogen or rare gas resonance lamp, and then mass selected. Temporal ion signals are recorded on a multichannel scaler including a short portion of background signal before the laser is fired. 

For isothermal measurements, using a Cahn Model RG thermo balance, the data acquisition system shown in Figure 12.3 was employed (11. 12). The system accepted up to four analog input signals, of which two were used for mass and temperature, respectively. The voltages were converted to frequency using a voltage-to-frequency converter, and four channels were simultaneously counted on four scalers for a predetermined time interval. 

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... 

Time it takes to amplify the signal and record it by a scaler. The resolving time of commercial scalers is of the order of 1 /xs. The time taken for amplification and discrimination is negligible. 

Due to the finite speed of signal processing, a photon eounter is unable to deteet a seeond photon within a certain dead time after the deteetion of a previous one. For gated photon counters or multichannel scalers, the dead time ean be as short as a nanoseeond. The relatively complicated signal proeessing sequenee in a TCSPC deviee leads to a much longer dead time. Older TCSPC deviees had dead times of the order of 10 ps. Newer, more advanced TCSPC modules are mueh faster but still have a dead time in the range of 100 to 150 ns. 

The scaled clock is most valuable for establishing a time base for experiments that cannot be started at a precisely known moment by external control. If the start of a spontaneously initiated experiment can be detected electronically, this signal can be used to enable the scaler logic of the clock. Thus, a time base precisely synchronized with the experiment is obtained. 

The photomultiplier output pulses were amplified, discriminated, and fed into a multichannel scaler, and OH fluorescence decays were signal averaged over 25-250 excimer laser shots. 

An output signal display. This, likewise, was provided by modules in the RIDL unit (scaler, model 49-30 and linear rate meter, model 35-9). The rate meter output is registered either on a Hewlett Packard 7132A dual pen or an L and N Speedomax H single pen recorder. 

Supplementary amplification. This may be unnecessary with newer scaler/rate meter instrumentation. Howeyer, the LSM-1 output signal was insufficient to operate the RIDL linear rate meter and was, therefore, further amplified through a Hewlett Packard 465A instrument. 

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