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Term Noise

Another source of drift results from incomplete mobile phase equilibrium with the stationary phase or incomplete mixing in the mobile phase preparation. Such drift always occurs on changing the composition of the mobile phase and to eliminate this drift, mobile phase should be pumped through the column-detector system until a stable base line is obtained. This problem can be [Pg.243]


There are three different types of detector noise, short term noise, long term noise and drift. These sources of noise combine together to give the composite noise of the detector. The different types of noise are depicted in figure 3. [Pg.162]

Short Term Noise consists of base line perturbations that have a frequency that is significantly higher than the eluted peak. Short term detector noise is not often a serious problem m liquid chromatography as it can be easily removed by an appropriate noise filter without affecting the profiles of the peaks. Its source is usually electronic, originating from either the detector sensor system or the amplifier. [Pg.162]

The detector noise is defined as the maximum amplitude of the combined short and long term noise, measured in millivolts, over a period of fifteen minutes. If a column 4.5 mm i.d. is employed, a flow rate of 1 ml/min is appropriate. The flow rate should be adjusted appropriately for columns of different diameters. The value for the detector noise should be obtained by constructing parallel lines embracing the maximum excursions of the recorder trace over the defined time period as shown in figure 4. The distance between the parallel lines measured in millivolts is taken as the noise level. [Pg.163]

The pressure sensitivity of a detector will be one of the factors that determines the long term noise and thus can be very important. It is usually measured as the change in detector output for unit change in sensor-cell pressure. Pressure sensitivity and flow sensitivity are to some extent interdependent, subject to the manner in which the detector functions. The UV detector, the fluorescence detector and the electrical... [Pg.164]

The short-term noise shown in Figure 2.5(b) arises primarily from the electronic components of the system and stray signals in the environment. Drift may also arise from electronic components of the system, particularly just after an instrument has been turned on and while it is stabilizing. [Pg.40]

Normally an oscillator circuit Is designed such that the crystal requires a phase shift of 0 degrees to permit work at the series resonance point. Long-and short-term frequency stability are properties of crystal oscillators because very small frequency differences are needed to maintain the phase shift necessary for the oscillation. The frequency stability Is ensured through the quartz crystal, even If there are long-term shifts In the electrical values that are caused by phase jitter due to temperature, ageing or short-term noise. If mass Is added to the crystal. Its electrical properties change. [Pg.128]

It is also possible to use an internal standard to correct for sample transport effects, instrumental drift and short-term noise, if a simultaneous multi-element detector is used. Simultaneous detection is necessary because the analyte and internal standard signals must be in-phase for effective correction. If a sequential instrument is used there will be a time lag between acquisition of the analyte signal and the internal standard signal, during which time short-term fluctuations in the signals will render the correction inaccurate, and could even lead to a degradation in precision. The element used as the internal standard should have similar chemical behaviour as the analyte of interest and the emission line should have similar excitation energy and should be the same species, i.e. ion or atom line, as the analyte emission line. [Pg.105]

Detectors of all types exhibit noise (IV). Noise is the amplitude (in detector response units) of the envelope of the baseline, which includes all random variations of the detector signal, whose frequency is on the order of one or more cycles per minute. Short-term noise is defined as that portion of the signal that consists of random periodic variations in the detector signal with a frequency of 1/min or greater. Long-term noise is similar to short-term noise except that the frequency range is between 6 and 60 cycles per hour. [Pg.34]

The Model 835 multiwavelength filter photometer (Fig.3.44) provides energy at 254 nm with a low-pressure mercury lamp and at 280,313,334 and 365 nm with a medium-pressure mercury source. Selected wavelengths between 380 and 650 nm are also available with a quartz-iodine light source. Absorbance ranges of 0.01-2.56 AUFS are provided. Short-term noise levels are 5 X 10-s AU with the low-pressure mercury source and 1 X 10 4 AU with the other lamps. The design and dimensions of the cell are the same as for Model 840. A 24-jtzl cell is standard with the medium-pressure mercury lamp and the quartz—iodine lamp. [Pg.88]

The momentary noise disturbance is averaged over time to obtain the noise disturbance . We will not use the term noise loudness because the value of y is taken such that the subjective quality model is optimized in that case does not necessarily represent noise loudness. The logarithm (log 10) of the noise disturbance is defined as the perceptual audio quality measure (PAQM). [Pg.309]

The ideal on-line detector has versatility, high sensitivity, the capacity for continuous monitoring of the column effluents, low noise level, wide linearity of response, stable baseline, insensitivity to flow rate and temperature changes, and response to all types of compounds. It is rugged, not too expensive, and is able to measure accurately a small peak volume without increasing its volume appreciably. The terms noise, sensitivity, and linearity are typically used in describing detector performance, as discussed below. [Pg.90]

Figure 7.14 Recognized types of noise short-term noise, long-term noise, and drift. Figure 7.14 Recognized types of noise short-term noise, long-term noise, and drift.
One advantage of a large time constant is decrease in short term noise, which is also called damping. The temptation to improve one s chromatogram by increasing the time constant to decrease the noise must be avoided. Also, consideration must be given to the time constants of all components in the detector network for example, the recorder must have a speed comparable to the detector itself. [Pg.204]

The thermal stability of any of the devices made from temperature-stable crystal cuts is degraded considerably when the device is coated with a polymeric film used for vapor sorption. Contact with a liquid may also introduce temperature variations that affect the short-term noise of the entire system. [Pg.145]

Detector noise is the term given to any perturbation on the detector output that is not related to an eluted solute. It is a fundamental property of the detecting system and determines the ultimate sensitivity or minimum detectable concentration that can be achieved. Detector noise has been arbitrarily divided into three types, short term noise, long term noise and drift all three of which are depicted in figure 4. [Pg.32]

The pressure sensitivity of a detector is extremely important as it is one of the detector parameters that determines both the long term noise and the drift. As it influences long term noise, it will also have a direct impact on detector sensitivity or minimum detectable concentration together with those other characteristics that depend on detector sensitivity. Certain detectors are more sensitive to changes in pressure than others. The katherometer detector, which is used frequently for the detection of permanent gases in GC, can be very pressure sensitive as can the LC refractive index detector. Careful design can minimize the effect of pressure but all bulk property detectors will tend to be pressure sensitive. [Pg.60]

Noise Level - (Nn) - The noise level of a detector is taken as the maximum amplitude of the combined short and long term noise taken over a period of 10 minutes it is usually measured in volts. [Pg.64]


See other pages where Term Noise is mentioned: [Pg.162]    [Pg.162]    [Pg.163]    [Pg.265]    [Pg.565]    [Pg.67]    [Pg.148]    [Pg.181]    [Pg.181]    [Pg.181]    [Pg.181]    [Pg.182]    [Pg.695]    [Pg.447]    [Pg.438]    [Pg.34]    [Pg.90]    [Pg.90]    [Pg.91]    [Pg.229]    [Pg.203]    [Pg.226]    [Pg.32]    [Pg.33]    [Pg.33]    [Pg.60]    [Pg.61]   


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Noise long term

Noise short term

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