544 INSTRUMENTATION: WATER AND WASTEWATER ANALYSIS
anions, and a variety of specific and nonspecific parameters
by automated analyzers. However, the instrumental appear-
ance and some unique functions related to unattended oper-
ations may differ.
Monitoring and data acquisition systems are also con-
sidered in this article. In the control of wastewater treatment
systems and plants, data may be obtained exclusively from
monitoring instrumental systems or a combination includ-
ing data from laboratory instruments via a laboratory data
system and/or from data entered through terminals.
Analytical instrumentation can be classified according
to principles based on various physical phenomena. These
general categories are spectroscopy, electrochemistry, radio-
chemistry, chromatography, and automated chemical analy-
sis. The instrumentation described in this article is organized
according to these categories.INSTRUMENTATION
Structure of InstrumentsAn instrument is a device that detects a physical property
or chemical entity through the conversion of a physical or
chemical analytical signal to an energy signal, usually elec-
trical, with subsequent readout of the energy signal.
Three main parts comprise an instrument: that is a chemi-
cal or physical sensor, signal conditioning circuits, and read-
out devices. The sensor develops a signal, usually electrical,
in response to a sample property and the signal conditioning
circuit modifies the signal in order to allow convenient read-
out display of the signal. Finally, a readout device displays
the signal, representative of the sample, in terms of a reading
on an analogue or digital meter, a recorder chart, an oscil-
loscopic trace, etc. Figure 1 delineates the three major partsand functions of an instrument, sample properties (measur-
and) to be measured, and instrumental criteria.Sensors A sensor, the primary contact of the instrument
with the sample, is a device that converts the input energy
derived from a sample property to an output signal, usually
electrical in nature. The relationship between the input energy
(measurand), Q 1 , and the output energy, Q 0 , is expressed in
the form:Q 0 f ( Q 1 ) (1)and is known as the transfer function. The sensitivity is given
in the equationS dQ 0 / dQ 1. (2)When the transfer function is linear, the sensitivity is constant
throughout the sensor’s range. However, the sensitivity (gain
or attenuation factor) is dependent on the value of the dif-
ferential fraction in equation 2. The sensor threshold is the
smallest magnitude of input energy necessary to obtain a
measurable change in the output.
Readout signals may be digital, D (discrete), or analog,
A (continuous), in form and are a function of the nature of the
input signal and the sensor and the design of the signal condi-
tioning circuits. These signals are interconvertible using A / D
or D / A devices. Fast reacting sensors and circuits, however,
are utilized for producing digital signals, where, formerly,
analog signals were obtained.
Two varieties of sensors, chemical and physical, are in
use on various instruments. The physical sensor allows the
conversion of physical energy from one to another. One
example is a photocell that converts an impinging light beamTABLE 3
Number of STORET listings for water analysisParameters by groups Example Number of
parameters in groupGeneral physical and chemical Alkalinity, COD, iron turbidity, zirconium 149
Physical observations Algae, foam, oil 12
Radionuclides Gross alpha and beta, strontium-90 141
Microbiological Coliform by MPH and MF, total plate count 18
Organic materials
Carbon adsorption data Chloroform and alcohol extractables 12
Natural organics Chlorophyll, tannins 4
Synthetic organics ABS, phenols 2
Halogenated hydrocarbons Aldrin, heptachlor, toxaphene 62
Phosphorated hydrocarbons Malthion, parathion 10
Miscellaneous pesticides Silvex 8
Treatment-related observations Available chlorine 6C009_005_r03.indd 544C009_005_r03.indd 544 11/23/2005 11:12:20 AM11/23/2005 11:12:20