General-purpose amplifiers

Typical specifications of several common operational ampAAers are provided in Table 1. The LM741 BJT amplifier consists of 20 transistors incorporated in a single chip, which is produced in high volume at a cost of less than 1.00. The 741 was the Arst general-purpose op amp and is still used since it is inexpensive, robust, and adequate for many routine applications at frequencies below about 10 kHz. However, more recent bipolar versions offer improved specifications e.g., the LMll op amp has a much lower input bias current, which is important in minimizing errors in many op amp applications. 

This chapter also deals with various types of auxiliary devices used in flow systems including power sources for general purposes and light somces, electronic circuits for controlling solenoid valves, peripheral instruments such as inductively coupled plasma mass spectrometry (ICP-MS) or gas chromatography (GC), and amplifiers. The devices described here have been of great help in constructing our own flow systems. 

X-ray spectrometry is generally carried out with Si(Li) detectors. The set-up is similar to that applied to y-ray spectrometry with i-Ge or Ge(Li) detectors cooling of the detector in a cryostat, operation in combination with a preamplifier, an amplifier and a multichannel analyser. The energy resolution is very good, as already mentioned in section 7.6, and makes it possible to distinguish the characteristic X rays of neighbouring elements. Some X-ray emitters that may be used for calibration purposes are listed in Table 7.6. 

Most transducers converting chemical concentration into an electrical signal have a nonlinear response for example, electrode potential and optical transmission are not directly proportional to concentration. In general, this nonlinearity is easily and simply corrected in equilibrium analytical measurements. However, it is considerably more difficult to instrumentally correct the response-versus-concentration function in reaction-rate methods, and often the correction itself can introduce significant errors in the analytical results. For example, the simple nonlinear feedback elements employed in log-response operational-amplifier circuits are not sufficiently accurate in transforming transmittance into absorbance to be used for many analytical purposes. 

AmpHfiers discussed in this chapter are limited to those that use solid-state devices as the active element since other types are discussed in Sections 7.7 and 7.8. In addition, amplifiers discussed in this section are presented in a way leading the reader to think that it is a section on RF amplifiers. This could not be further from the truth. Examples and presentations made here are meant to be general, using the general case where carrier frequencies are not zero. The same rules apply to amplifiers, whether they are used for baseband purposes, in which case the carrier frequency is zero, or are used as RF amplifiers, in which case the carrier frequency is not zero. 

---