Dead band, instrument

The mechanical ball and disc integrator is rapid, precise, and accurate. Reproducibility between instruments, individuals, and laboratories is really quite good. The integrator itself is quite economical (less than 1000) but it does require a recorder compatible with the integrator. The limitation in the accuracy appears to be in the recorder itself since it is the recorder pen drive itself that actuates the integrator. Thus any dead band or damping in the response of the recorder will be reflected in the performance of the integrator. 

From a dynamic response standpoint, the electronic adjustable-speed pump has a dynamic characteristic that is more suitable in process control applications than those characteristics of control valves. The small amplitude response of an adjustable-speed pump does not contain the dead band or the dead time commonly found in the small amplitude response of the control valve. Nonlinearities associated with friction in the valve and discontinuities in the pneumatic portion of the control valve instrumentation are not present with electronic variable-speed drive technology. As a result, process control with the adjustable-speed pump does not exhibit limit cycles, problems related to low controller gain, and generally degraded process loop performance caused by control valve nonlinearities. 

Pressure switch, hermetically sealed, fixed dead band, snap action, stainless steel. Dwyer Instruments Mercoid switch DS7341- 153-23E 1... 

The third point listed above is of utmost importance if the theoretically expected improvement in separation performance should be exploitable with a real instrument. Apart from the inherent contribution of the separation column itself (variance crcol2), overall band broadening (a2) is also caused by the sample injector (crin2), the finite length of the detection volume (adet2), and by any contributions of dead volumes (adv2) due to fittings etc. (see for example [22] ... 

ESEEM studies require microwave pulse widths that are short in comparison with the period of the highest frequency modulation to be studied. 90° pulse widths of 16-20ns are typical for X-band ESEEM studies where the period of the proton Larmor frequency is about 70 ns at g = 2. One typically adjusts the sample probe s microwave coupling to the maximum overcoupling position, sets up a two- or three-pulse ESE sequence, and optimizes the echo amplitude as observed on an oscilloscope or transient recorder display by adjusting the pulse power and reference arm phase. If sensitivity is low, the probe coupling can be adjusted some to increase the probe Q without giving up too much in terms of the instrument s dead-time. 

The instrument band-spreading (ITec) can be measured by replacing the column with a zero dead-volume restrictor, injecting a very small volume of sample, and measuring the resulting peak width. Table 17-5 provides band-... 

Obviously, designs of capillary gas chromatographs must be more carefully executed than those of packed column instmments. The chief reasons for this are the very low flow-rates used and the overall small volumes of capillary columns. Under such circumstances, the units connecting the column to either the inlet or detector parts must virtually be absent of any dead volumes. Inlet systems with clean geometry are also required to introduce the sample as the narrowest possible band into the first column section. A constant dilemma of the manufacturers of modern instruments has been whether to design universal instruments or those usable just for certain column types. It seems now that the production of dedicated capillary instruments is becoming common. Alternatively, instruments can be provided with multiple inlet and detector capabilities. Numerous laboratories also successfully modified the earlier versions of instruments into capillary gas chromatographs. 

The dead volume of an isocratic instrument is the volume between the injection point and the detector, excluding the column. It is the volume of connecting capillaries, fittings and detection cell. Since the sample is present in this part of the instrumentation, its total volume should be minimized. You will then have only a small amount of dilution of your sample, thus minimizing band broadening. How do you measure the dead volume ... 

Fig. 18.15. Compensated infrared spectra of four volatile chemicals in carbon disulfide. Absorption bands of benzene are observed at 1036 cm" and 671.1 cm"methyl chloroform at 1085 cm" and 710.2 cm" trichloroethylene at 927.6 cm" and carbon tetrachloride at 781.3 cm" and 762.2 cm". Note the solvent (CS2) absorbs all the radiation between 877.2 cm" and 833.3 cm" at this path length (12.5 mm), which renders the instrument "dead in this region. (Stewart and Erley, 1965.)...

With the desire for high-speed separations on short columns, [xGC systems must be carefully designed in order to minimize sources of extra-column band broadening such as dead volumes at connection points and within detectors, large injection pulses, and non-uniform flow patterns. The interface of the chip with instrumental components is extremely important and integration of all of the components directly with the column is preferred. 

FIGURE 5.5 Golay plots for a 5.0-m-long, 0.25-mm-i.d. thin-film column using hydrogen carrier gas showing the effects of extracolumn band broadening defined by the total instrumental dead time Af. A binary diffusion coefficient of 0.4 cm /s and a retention factor of 2.0 are assumed. 

A. Note how the sample was run physical state, thickness, mulling agent or solvent. Mark the positions of the strong bands of any mulling agent or solvent because the instrument may be dead there and give no information. 

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