ABSTRACT
Sensors and transducers are crucial in instrumenting an engineering system. Sensors may be used in an engineering system for a variety of purposes. Essentially, sensors are needed to monitor and learn about the system. This knowledge will be useful in many types of applications, including the following:
1.Process monitoring 2.Operating or controlling a system 3.Experimental modeling (i.e., model identification) 4.Product testing and qualification 5.Product quality assessment 6.Fault prediction, detection, and diagnosis 7.Alarm and warning generation 8. Surveillance
Specifically in a control system, sensing is used for such purposes as
1.Measuring the system outputs for feedback control 2.Measuring some types of system inputs (unknown inputs, disturbances, etc.) for feedforward
control 3.Measuring output signals for system monitoring, parameter adaptation, self-tuning, and supervi-
sory control 4.Measuring input and output signal pairs for experimental modeling of the plant (i.e., for system
identification)
The terms sensor and transducer are often used interchangeably to mean the same thing. However, strictly, a sensor senses the quantity that needs to be observed or measured (called measurand) while the transducer converts into a form that can be observed or used in a subsequent operation. Except when necessary, we will use the terms sensor and transducer to mean the same device. Proper selection and integration of sensors and transducers are necessary and significant tasks in instrumenting an engineering system. Sometimes, we may have to design and develop new sensors or modify existing sensors, depending on the needs of the specific application. Such activities are based on a set of performance specifications for the required sensors. The characteristics of an ideal sensor and transducer are presented in Chapter 3. Even though a real sensor will not be able to achieve such ideal behavior, when designing and instrumenting an engineering system it is desirable to use the ideal behavior of the system components as a reference with respect to which the performance specifications may be generated and presented. A model is useful in representing the behavior of a sensor. Specifically, a model may be used to analyze, simulate, design, integrate, test, and evaluate a sensor.
