Digital switch over

Depending on the availability of the number of pH meters this may be a class exercise (demonstration), or 6-8 students may use one pH meter. Add 5 mL of 0.1 M acetic acid to a dry and clean 10-mL beaker. Wash the electrode over a 200-mL beaker with distilled or deionized water contained in a wash bottle. The 200-mL beaker serves to collect the wash water. Gently wipe the electrode with Kimwipes (or other soft tissues) to dryness. Insert the dry electrode into the acetic acid solution. Your pH meter has been calibrated by your instructor. Switch on the pH meter and read the pH from the position of the needle on your scale. Alternatively, if you have a digital pH meter, a number corresponding to the pH will appear (Fig. 22.2). 

According to Equation 52, the phase of the Fourier transformed signal in the frequency domain changes over the bandwidth of the instrument. This is, however, not the only phase problem that occurs. In addition, a frequency-dependent phase shift is introduced because the data collection can normally begin only a certain time (ca. 100 nsec) after the pulse is switched off. This and other phase shifts due to the use of band limiting filters are well-known in NMR and can easily be corrected with a digital computer. The true absorption spectrum, Sg(w), is obtained as a linear combination of the cosine and.sine Fourier transforms of the signal in the time domain Scos( ) SsinM respectively. 

In addition to power-line coupled noise, computers and cathode-ray-tube monitors can be a troublesome source of interference in many clinical and laboratory situations. Digital logic electronics often involve fast switching of large currents, particularly in the use of switching-type solid-state power supplies. These produce and can radiate harmonics that spread over a wide frequency spectrum. Proximity of the amplifier or the monitored subject to these devices can sometimes result in pulselike biopotential interference. 

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