Pulse counter

The instruments for polymer HPLC except for the columns (Section 16.8.1) and for some detectors are in principle the same as for the HPLC of small molecules. Due to sensitivity of particular detectors to the pressure variations (Section 16.9.1) the pumping systems should be equipped with the efficient dampeners to suppress the rest pulsation of pressure and flow rate of mobile phase. In most methods of polymer HPLC, and especially in SEC, the retention volume of sample (fraction) is the parameter of the same importance as the sample concentration. The conventional volumeters— siphons, drop counters, heat pulse counters—do not exhibit necessary robustness and precision [270]. Therefore the timescale is utilized and the eluent flow rate has to be very constant even when rather viscous samples are introduced into column. The problems with the constant eluent flow rate may be caused by the poor resettability of some pumping systems. Therefore, it is advisable to carefully check the actual flow rate after each restarting of instrument and in the course of the long-time experiments. A continuous operation— 24h a day and 7 days a week—is advisable for the high-precision SEC measurements. THE or other eluent is continuously distilled and recycled. 

In period measurement a second crystal oscillator is essentially used as a reference oscillator that is not coated and usually oscillates at a much higher frequency than the monitor crystal. The reference oscillator generates small precision time intervals, with which the oscillation duration of the monitor crystal is determined. This is done by means of two pulse counters the first counts a fixed number of monitor oscillations m. The second is started simultaneously with the first and counts the oscillations of the reference crystal during m oscillations of the monitor crystal. Because the reference frequency F,. is known and stable, the time for m monitor oscillations can be determined accurately to 2/F,.. The monitor oscillation period is then... 

Pulse counter, Heater controller and Communication module... 

Fig. 32. Block diagram of a pulse counter for radio-isotope measurements. From ref, 246.

The three-compartment source was attached to the analyzer tube of a 6-inch radius 60° sector magnetic deflection mass spectrometer. Differential pumping was used between the source and analyzer regions. The ion detector was a 14-stage electron multiplier coupled to both a vibrat-ing-reed electrometer and a pulse counter (38). The electrometer was connected to a strip-chart recorder and the counter to a printer. This arrangement allowed any range of e/m to be scanned or a given peak to be monitored. 

This is the region where "proportional counters" operate, and current is proportional to radiation intensity. Total current flow per ionizing event is much larger than in the ion chamber region ("Gas multiplication or amplification"). Detectors operated in this region usually are "pulse counters" rather than... 

For data input in fixed cycle operation the AMI and Siemens package type 1907 shown in Fig. 28 has been designed. With this device and a few additional components a pulse counter, frequency meter, chronometer or digital voltmeter can be built. 

The polymer to be fractionated is dissolved in a solvent + nonsolvent mixture, and this solution (feed) is extracted continuously by a second liquid (extracting agent, EA), which contains the same solvent components as the feed (Fig. 6). The fractionation can be performed with a pulsed counter-current extraction apparatus. Fractionation is achieved by the fact that the molecules are distributed over the counter-current phases according to their chain length. The feed leaves the colunm as gel and the EA as sol. 

FIGURE 9.9 XRF of nominal lead shot measured at Virginia Commonwealth University using a Kevex Quantex ISI-130 SEM-EDX electron microscope with XRF attachment and a 20 keV excitation beam. The y-axis is in counts because the intensity was measured with an internal pulse counter and the x-axis is given directly in kiloelectron volt as reported with the software associated with the instrument. The spectrum was run by James Spivey at VCU. The XRF spectmm of the lead shot reveals it is mainly lead but contains other metals as well. Note the presence of poisonous As and Pb. Thanks are due to Rhonda Stroud of the Naval Research Laboratory for interpretation of the spectrum and the assignment of the peak between As and Pb at 1.740 keV as due to a K line from Si. 

A pulse input consisting of a train of pulses can be digitized by using a pulse counter, which measures the pulse frequency and converts pulse frequency to a digital representation. The computer maintains an accumulator for the pulse counts its output after a period of time is proportional to the pulse frequency (Johnson, 2005). For example, a turbine flow meter utilizes a pulse counter to measure the rate of fluid flow. In one full revolution, a... 

Chloride is titrated with silver ions, which are generated from a silver anode at constant current. The end point is detected by a sudden increase in current through a separate set of silver electrodes, caused by the first excess of free silver ions this current activates a trigger circuit to stop the pulse counter. The total number of pulses counted is a direct measure of the amount of chloride in the sample. 

B. J. Jun, et al., "Real Time Reactivity Measurement Using Neutron Pulse Counter," Proc. Korean Nucl. Soc. Spring Meeting, May 27, 1989, SuWon, 1 10. 

The fission-chamber signals are fed to conventional preamplifiers, A-1 linear amplifiers, logarithmic count-rate meters and a dual-pen recorder. For initial reactor startup before gamma-neutron reactions provided a sizable neutron source, the fi.ssion-chamber output was u.scd to drive a low-range pulse counter. 

The large thermal-neutron cross section for this event makes the instruments exceedingly sensitive. The response of the boron-coated current chamber is measured as a small ionization current which is proportional to the neutron density at the chamber location. The second type of detector, a BF3 proportional counter, is a pulse counter. Each event (reaction) occurring in the counter yields a short voltage pulse which is recorded on a conventional scaler. The rate at which these events occur is proportional to the neutron density at the position of the counter. 

As pointed out previously, this is a pulse counter, so individual measurements must be made at selected points. You may choose your locations for flux measurements in a manner that seems to you to give the best determination of the neutron distribution. The counts taken over a selected time interval at the different counter positions are recorded in a MPC scaler. 

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