Electronics and readout

The radiant energy from the source must be converted into an electrical signal for amplification and measurement by the readout system. This conversion is undertaken almost universally by a photomultiplier tube. 

Generally speaking a manufacturer will fit a photomultiplier tube which has adequate response across the whole spectrum. This means that at the extremes of the wavelength range the performance will be tailing off and it may be worth considering more powerful photomultiplier tubes for dedicated work at the red end, for cesium and rubidium for instance. Photomultiplier response curves are available from manufacturers such as Hammamatzu and Philips. 

It is necessary that the hollow-cathode lamp source be pulsed or modulated at a certain frequency and for the amplifier to be locked in to this frequency to permit discrimination against the continuous emission signal coming from the atomiser. Only the resonance radiation from the lamp must be seen. In modem digital electronic instruments the lamp cycle is controlled by a sophisticated electronic clock which is sampled to provide the short pulses of 

The introduction of a simple microprocessor into an atomic absorption spectrometer has increased flexibility and ease of operation. The following benefits have been introduced (a) Easier operation via a keyboard and push 

The technology is now available for many more instrument functions to be selected both on the main instrument and peripheral devices such as an electrothermal atomiser or autosampler. Programmes for instrument setting and data processing can be stored, for example, on magnetic cards. Although, as already indicated, the actual speed of analysis may not be vastly improved, the advantages lie in the better reliability and accuracy obtainable and in the possibility of more efficient use of the time of a skilled analyst. 

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An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

Figure 3 Principle of construction of atomic absorption spectrometers. (A) Single-beam spectrometer with electrically modulated lamp radiation (B) double-beam spectrometer with reflection and splitting of the primary radiation by a rotating, partially mirrored quartz disk (chopper). 1 - radiation source, 2 -sample cell (atomizer), 3 - monochromator, 4 - detector, 5 -electronics and readout (by permission of Wiley-VCH from Welz B and Sperling M (1999) Atomic Absorption Spectrometry, 3rd, completely revised edition. Weinheim Wiley-VCH).

The pressure transducer shall have a minimum operational range from 0 to 177 kPa (0 to 25.7 psi) with a minimum resolution of 0.1 kPa (0.01 psi) and a minimum accuracy of 0.8 kPa ( 0.12 psi). The pressure measurement system shall include assodat electronics and readout devices to display the resulting pressure reading. 

In addition to the Mossbauer data, SDDs allow the simultaneous acquisition of the XRF spectrum, thus providing data on the sample s elemental composition. A new control- and readout-electronics for MIMOS llA allows spectra acquisition at highest possible count rates available at a total detector area of 360 mm. ... 

The Erweka and Schleuniger testers operate on a counterweight principle that eliminates fatigue, if not frictional, losses. The latter of these two devices is supplied calibrated and a mechanical tablet is available for periodic recalibration. More recently, testers have been introduced that measure the load being applied to the tablet by means of load cells and therefore facilitate direct electronic digital readout. This eliminates the two major sources of error referred to above and permits recording of production of hard copies of the test results. 

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