AMAZON multi-meters discounts AMAZON oscilloscope discounts Sensors, transducers, and transmitters are perhaps the most important parts of industrial control systems. They are used in process control systems as well as motor control and motion control systems. You will find them in virtually every system because they provide feedback information about how well the system is doing. A sensor is defined as a device that is sensitive to motion, heat, light, pressure, electrical, magnetic, and other types of energy. A transducer is defined as a device that can receive one type of energy and convert it to another type of energy. This means that a transducer may include a sensor to sense the amount of pressure, and a circuit to convert the amount of pressure to an electrical signal and transmit it to an electrical control system where it's used as the process variable (PV) or feedback signal. Since transducers can convert one type of energy to another, it's important to be able to identify all the types of energy. it's also important to understand that the final form of energy is generally something that is compatible with electronic circuits. This means that the output of the transducer must be able to change voltage, current, resistance, frequency, capacitance, or inductance so it's compatible with electronic circuits. The major forms of energy that sensors can detect can be classified as motion, temperature, light, pressure, electrical, magnetic, chemical, and nuclear. There are several variations of each of these and times when they overlap slightly such as when motion causes a change in pressure, or when light causes a change in temperature. It is important to understand that a wide variety of sensors can measure temperature, but one type may be more useful to an electronic circuit because it converts its temperature measurement to an electrical signal compatible with electronic circuits. e.g., the temperature sensor may be a thermocouple or a glass bulb containing mercury that can sense changes in temperature. Since the thermocouple converts the change in temperature to a change in millivolts, and the mercury bulb converts the change in temperature to the height of the column of mercury, the thermocouple will be more useful to an electronic circuit because the change of voltage can be easily transmitted as a feedback signal.A transmitter is a device that can convert a very small signal to a more usable signal. The transmitters for the sensors used as industrial feedback signals must typically convert very small electrical signals such as microvolts (µV), millivolts (mV), milliamps (mA) or frequency into larger voltage and current signals such as 0-10 volts or 4-20 mA. The transmitter generally uses devices such as op amps to amplify and linearize the output signal. The transmitter may also provide a zero and span circuit that allows the signal to be calibrated with other parts of the electrical system such as the single-point controller. It is important to understand that all of the sensors and transducers are grouped into a broad category called instruments. The number of sensors and transducers available for use in modern industrial systems seems almost unlimited. it's necessary to classify them in groups that represent the type of energy conversion that is used, such as temperature, motion, light, and so on. The second type of classification is defined by the type of electrical signal that the device produces, such as voltage, current, frequency, and so on. It is easier to understand all of these devices and how they are used in electronic circuits in industrial applications if you think of them in groups that represent their theory of operation, and the type of signal that they produce. Since these two categories are very tightly defined, you will find that you only need to learn a few theories, and you can transfer this knowledge and be able to explain the theory of operation of virtually every sensor and transducer that you find. This will also be useful when you must design engineering systems or troubleshoot these devices. Troubleshooting the electronic part of sensors and transducers is made easier since sensors produce limited types of electrical signals that you will be familiar with. The table below shows the type of energy source in the first column and the type of sensor or transducer that converts this form of energy to voltage or current. The third column shows the type of sensor or transducer that changes the original source of energy to a change of resistance or impedance.
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