Oscilloscopic measurements

Figure 2.56 Photocurrent decay (oscilloscope measurement) during the first initial oxidation phase of n-Si(lll) in dilute NH4F, pH 4 W-l lamp, ms shutter in this first oxidation phase, about 10 monolayers of oxide are formed (see text).

A unique feature of TRMS is that both identities and quantities of ions may be studied in the time domain. For an engineer, the relationship between conventional MS measurements and TRMS is like the relationship between multimeters and oscilloscopes multimeters only indicate average electric properties while oscilloscopes measure and record fast changes in electrical signals over time. By analogy, TRMS uses a high-performance chemical detector (mass spectrometer) to study the dynamic phenomena of atoms, molecules, and ions during reactions. 

Other Measuring Devices. One of the most valuable devices in the arsenal of electrical measurement is the oscUloscope, which is available in both analogue and digital models. Like a typical meter, the oscilloscope measures electrical inputs, but it also has the capability to display the reading as a dynamic trace on a display screen. The screen is typically a cathode-ray tube (CRT) display, but later versions use liquid crystal display (LCD) screens and even can be used with desktop and laptop computers. 

Disconnect the pulse generator and, again using the oscilloscope, measure the rms (root-mean-square) noise voltage, at the linear amplifier output. 

Using an oscilloscope, measure the height of the pulses, Vp, at the output from the linear amplifier. The system gain is then V /E. ... 

Our results are only semiquantitative for a number of reasons including the fact that the oscilloscopic measurement of AA/A is not of very high accuracy. Furthermore our conductance study (7) shows... 

The mean difference between values estimated at the EVM with those based on the oscilloscope measurements was 8.53%. Every measurement was repeated 5 times to assess repeatability, with a result of 0.34% of mean deviation. 

There are two categories of equipment which determine the selection of equipment general-purpose and special-to-type equipment. It should not be necessary to specify all the general-purpose equipment needed to perform basic measurements, which would be expected to be known by appropriately trained personnel. You should not need to tell an inspector or tester which micrometer, vernier caliper, voltmeter, or oscilloscope to use. These are the tools of the trade and they should select the tool which is capable of measuring the particular parameters with the accuracy and precision required. However, you will need to tell them which device to use if the measurement requires unusual equipment or the environmental conditions prevailing require that only equipment be selected that will operate in such an environment. In such cases the particular devices to be used should be specified in the test or inspection procedures. In order to demonstrate that you selected the appropriate device at some later date, you should consider recording the actual device used in the record of results. With mechanical devices this is not normally necessary because wear should be detected well in advance of there being a problem by periodic calibration. 

Perfluoroalkane-225 (PGR, Gainesville, FL) was admitted through a glass inlet system to provide reference peaks. Analytical and reference peaks for the nitrosamines studied are shown in Table I. Sample and reference peaks were scanned alternately at a repetition rate of approximately 1 sec and were monitored on an oscilloscope. When the nitrosamine peak appeared, the oscillographic recorder chart drive was engaged and remained on until the peak disappeared. Nitrosamine quantities were estimated by comparing the sum of sample peak heights measured from the chart (usually 10 to 20 values) with values derived from injection of standard solutions. 

In transient measurements one must record rapidfy changing currents or potentials. In the past, cathode-ray oscilloscopes have been used for this purpose (at present, improved recording devices or computers are used as well), hence the term oscillographic polarography (or oscillographic voltammetry). This term is unfortunate since it reflects only the device used to record the results, rather than the essential features of the method used for the measurements. 

Further, the operator must be able to choose the drop lifetime and the scan parameters, viz., the starting potential, direction (cathodic or anodic), rate and end potential, together with the sensitivity of the current measurement and the amplification in the ohmic cell resistance compensation circuit. Convenient additional facilities are (a) display of the polarogram on an oscilloscope, (b) delivery of hard copy of the polarograms on a chart recorder and (c) repeated recording of the polarographic curve for the same sample. 

The simplest of the methods employing controlled current density is electrolysis at constant current density, in which the E-t dependence is measured (the galvanostatic or chronopotentiometric method). The instrumentation for this method is much less involved than for controlled-potential methods. The basic experimental arrangement for galvanostatic measurements is shown in Fig. 5.15, where a recording voltmeter or oscilloscope replaces the potentiometer. The theory of the simplest applications of this method to electrode processes was described in Section 5.4.1 (see Eqs 5.4.16 and 5.4.17). 

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