Interference common-mode

Common-Mode XYZ Channel Noise A noise source or impairment that affects all output channels more or less equally (known as a common-mode characteristic) could be associated with the seismometer electronics that serve common functions such as power conversion and control circuits, but is more likely an external common-mode effect, such as noise induced on all input channels to the digitizer by electrical interference. Common-mode XYZ cannot be problems with any or all of the internal Galperin axis elements, because these would manifest in the U, V, W, or Z directions, respectively, never in the direction corresponding to equal XYZ signals. 

Cell Division Inhibitors. The most common mode of action of soil-appHed herbicides is growth inhibition, primarily through dkect or indkect interference with cell division (163). Such growth inhibitory activity is the basis for most pre- or post-emergent herbicides intended to control germinating weed seeds. In germinating seeds, cell division occurs in the meristems of the root and the shoot. Meristematic cells go through a cycle... 

Instruments with a balanced input circuit are available for measurements where both input terminals are normally at a potential other than earth. Further problems arise due to common-mode interference arising from the presence of multiple earth loops in the circuits. In these cases the instrument may need to be isolated from the mains earth. Finally, high-frequency instruments, unless properly screened, may be subject to radiated electromagnetic interference arising from strong external fields. 

FIGURE 7.12 Typical electromagnetic interference (EMI) filter schematic and outline the filter yields 60 dB common-mode attenuation and 50 dB transverse mode attenuation between 100 kHz and 1 Mhz. 

The frequency converter s voltage wave form can be changed to a degree at the frequency converter. Using an output filter also alters voltage wave form. These filters were mainly developed to minimize high-frequency common-mode interference voltage, but they reduce circular currents as well. 

Both NH3 oxidizers and N02 oxidizers, but especially the former, are susceptible to inhibition by a wide range of compounds, and several different modes of action have been documented (Bedard and Knowles, 1989). The two most common modes of inhibition are (1) interference with the active site of the primary enzyme (i.e., NH3 monooxygenase in AOB N02 oxidoreductase in NOB) by compounds that share structural homology with NH3 or N02 and (2) metal binding compounds, which interfere with the action or availability of copper in the NH3-oxidizing enzymes. In both NH3- and N02 -oxidizers, the susceptibility to inhibitors by key enzymes forms the basis of some methods used to measure the rate of nitrification in the environment (see above). 

Thus it can be seen that normal pulse polarography is potentially the least sensitive to interference from adsorption effects of the common modes of polarography. 

FIGURE 9.10 Driven-right-leg circuit reducing common mode interference. 

In ECG monitoring, for example, the common-mode interference on the body sums with the arm-lead potentials Vra we calculate under these circumstances, we get... 

In practice, this interference cancellation process works fairly well however, the assumption that the power-line-induced signal is common mode (uniform) over the body does not hold perfectly in all situations. Slight differences in its phase or amplitude over the subject s body when in close proximity to some electric field source or unbalanced electrode impedances can cause this cancellation process to be less than perfect. Some line noise may still pass through into the recording. Usually, improvements in skin electrode preparation can remedy this problem. 

Figure 6. Common mode interference propagation path of double three-level explosion-proof converter main circuit...

Electric interference in fhe environment induces current into the body, which is then picked up by the biopotential amplifier as a common-mode voltage [27]. The CMRR property of the amplifier is essenfial for reduction of the common-mode voltage [25]. Finally, the driven right leg design [27], described earlier, can be optionally used to reduce further the common-mode voltage and the effective interference. 

Figure 9.6. Differential amplifier performance with common-mode interference signals, (a) Upper trace 10-kHz sine wave with superimposed common-mode noise as amplified by conventional amplifier lower trace same signal amplified by differential amplifier, (b) Upper trace 10-kHz square wave with superimposed 60-Hz hum and broad-band noise as amplified by single-ended amplifier middle trace same signal as amplified by differential amplifier lower trace residual noise removed by filtering, (c) Circuit schematic for transistor differential amplifier with constant-current emitter stage, (d) Vacuum-tube differential amplifier in long-tailed pair configuration. (See Ferris, 1963.)...

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