Read-Out Devices

The simplest read-out device presently in use for atomic absorption is a visually observed meter with a galvanometer-type movement, usually used with a series resistance to read voltage. By using variable potentiometers in the output circuit of the amplifier, it is simple to adjust the meter to full-scale reading on a sample blank and zero when no signal enters the entrance slit of the monochromator. The signal produced by the sample can then easily be obtained in terms of percentage transmittance if the meter scale is 0-100. 

Digital read-out devices also are used in atomic absorption spectroscopy. The digital voltmeter frequently uses a nixie tube display. These devices call for the operator to record a visually displayed number. 

Read-out devices that produce printed data also are available. These devices produce a printed report of the analytical results which can be treated by any desired computer calculation to present final results of the analysis. The data are not subject to human error and a permanent record is obtained. 

When analytical atomic absorption was in its early stages of development much information was circulated concerning the freedom of the method from interference effects. This led early users of the technique to assume no interferences occurred in atomic absorption. In fact, atomic absorption has as many types of interferences as flame emission, although in some cases the magnitude of the interference is smaller. Any factor that affects the ground state population of the analyte element can be classed as an interference, since, in atomic absorption, the concentration of the analyte element in the sample is considered to be proportional to the ground state atom population in the flame. Any other factor that affects the ability of the atomic absorption instrument to read this parameter also can be classed as an interference and proper control of these effects is necessary to obtain correct analytical results. The common types of interferences that occur in atomic absorption are the topics of this section. 

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Frequently recalibrate and test all instruments, read-out devices, sensors and alarms. 

Instrument Productivity. The number of samples that can be processed by one instrument in a given period of time is determined by the length of time each sample has to be read by the photodetector or other read-out device, or by the number of cuvets per unit time which pass the detector. For example. 

L = Amplifier to amplify the feeble electrical impulse and a built-in direct read-out device. 

Every day of our lives we run across LCs. They are commonly found in computer monitors, digital clocks, television screens, and other read-out devices. 

Field turbidity meters may be part of the multiple field parameter meters or they may be available as standalone units. A typical meter has a range of 0-1000 NTUs and an accuracy of + 2-3 percent. Some meters have a submersible turbidity probe that allows in situ measurements, while others require sample collection for ex situ measurements. To perform an ex situ measurement, we pour the sampled water into a glass measuring cuvette (usually a vial with a cap), seal it, and insert into a measuring chamber of a portable nephelometer. The read-out device will give us a turbidity value in NTUs. 

It has proven feasible to take the electrical output from photocells or phototubes and either with or without amplification record the magnitude and duration of the output. The recording may be made either in the form of a line tracing on a moving chart or may be converted to numerical values and printed by a read-out device. Further refinements can be supplied in which the instrument converts optical densities (or transmittance units) to concentration values. More intricate recording colorimeters or spectrophotometers are also available for continuous scanning and recording of complete spectra from ultraviolet to infrared. No further discussion of these will be attempted since they do not serve a normal function in routine clinical chemistry laboratories. 

The photodiodes of the imagers presented in US-A-4566024 are formed in a p-type HgCdTe substrate by diffusing n-type impurities from two opposite faces, a front face and a rear free, of the substrate. The photodiodes can be connected to a read-out device by a flip-chip bonding process on the rear face of the substrate and still be illuminated from its front free. 

The problem of cross-talk between adjacent photodiodes is solved in JP-A-2303160 by forming islands of HgCdTe, comprising photodiodes, on a CdTe substrate and then bonding them to a read-out device by a flip-chip bonding process. 

With substrate 10 attached to detector elements 16, the complete detector assembly 30 is attached to a CCD 20 or another read-out device using bump contacts 18. Substrate 10 and adhesive 12 are then removed using an appropriate solvent such as acetone. 

A read-out device, comprising an input region 23, is formed in a silicon substrate 21. A positive photo-resist film 29A, a negative photo-resist film 29B and a second positive photoresist film 29C are patterned into a spacer. Connecting bumps 34 are applied and a detector chip 31, comprising photodiodes 33, is bonded to the silicon chip by pressing the two chips together. Finally, the photo-resist films 29A, 29B and 29C are removed. 

In JP-A-63116459 an imager is made up of photodiodes formed in an HgCdTe substrate. The photodiodes are placed in columns and rows. The number of connections between the HgCdTe substrate and a silicon substrate, comprising a read-out device, is reduced by connecting the anodes of the photodiodes in each row to each other and connecting the cathodes of the photodiodes in each column to each other. 

A different approach to the problem of connecting terminals of individual detectors formed in an HgCdTe layer with corresponding terminals of a read-out device integrated in a semiconductor substrate is to provide connections via holes formed through the thickness of the HgCdTe layer. One particular technique is known as the loophole technique. The characteristic features of this technique are that an HgCdTe substrate is adhered to a... 

An HgCdTe substrate 1 comprises photodiodes 2 placed in rows and columns. The anodes of all photodiodes belonging to the same row is connected to a row line 6 and the cathodes of all photodiodes belonging to the same column are connected to a column line 8. The row lines and column lines are connected to a read-out device formed in a silicon substrate 3. 

The instrumentation used for atomic emission spectroscopy (AES) consists of an atomization cell, a spectrometer/detector and a read-out device. In its simplest form, flame photometry (FP), the atomization cell consists of a flame (e.g. 

Have technology available for, and develop skills to use, analytical methods for recognition and confirmation of threat chemicals. With CN as vapor, and as previously noted, odour is not a totally reliable recognition property because of the inability of some individuals to recognize the characteristic odour. Testing should be carried out to discover those who have CN anosmia. For the detection of atmospheric HCN, Draeger tubes are available but there is a need for portable instant read-out devices to quantitatively measure CN in the atmosphere at incident sites. Methods for the on-site and rapid detection of systemic CN intoxication by analysis of small blood samples need to be developed and refined. 

The frequency response of the system is a high-pass filter, since, for tor 1, Vo(ift))/X] (io)) = E/xo, which is a constant. However, the response drops off for low frequencies, and it is zero when at = 0. This frequency response is sufficient for a microphone that does not measure sound pressures at frequencies below 20 Hz. The input impedance of the read-out device must be high (10 MS2 or higher) in order to achieve a required low-frequency bandwidth. Capacitance sensors are not suitable for measuring most physiological signals because the frequency spectra of these signals have dominant low-frequency components. 

The results can be placed on any one of several read-out devices, a strip chart recorder, a digital voltmeter, or a printed report from a computer. 

A variety of read-out devices are used. Frequently a galvanometer with a 0-100% T scale is used. Digital read-out also is used and arrangements for chart recording of line intensities are available with most densitometers. Recently instrumental design has switched to solid state devices to serve as amplifiers of the signal from the photoreceptor. 

The interpretation of spectra requires accurate information on spectral line intensities this is essential for quantitative analytical data. Three general procedures are used to obtain this information (1) visual inspection of spectral lines, (2) photographic recording of spectra, and (3) the use of a photocell and associated amplifiers with some type of read-out device. Visual inspection of spectral lines is possible but inconvenient and not very accurate. Photographic recording of spectra is a very common and useful technique since a spectral region may be photographed that includes many spectral lines of many elements. The photoplate also becomes a permanent record of the spectra. 

Light-sensitive phototubes also can be used to determine relative spectral line intensities. Two approaches are used for this purpose. The large, direct reading spectrometers use a battery of phototubes, one for each spectral line desired, located at the individual focal points. Usually the output of the phototube is collected over a specified time interval and stored in a capacitor. After exposure the capacitor is discharged into some type of read-out device. This method integrates the total energy over a time interval to provide a measure of spectral energy. 

Flame excitation methods, coupled with simple read-out devices, provided high sensitivity and high reliability for the determination of the alkali metals in simple liquid systems. Further development of burners and aspirators, higher flame temperatures, better spectral isolation using gratings or prisms, and more sensitive detection and read-out devices has increased the list of elements that can be detected by flame excitation to between 50 and 60. 

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