Photo Optical Modulator: Photo Optical Modulator – The principle of an optical dc chopper is illustrated in Fig. 14.42. Devices of this type have been used widely in infrared signal detectors, whose output is a slowly varying dc product. The properties of the parallel connected photo resistor are such that the device produces a decrease …
Solid State Modulator/Demodulator Circuit: A solid state modulator/demodulator circuit is shown in Fig. 14.41. The transformer T is driven by an ac source and couples each secondary connected to the two transistor pairs, Q1 – Q2 and Q3 – Q4. During the first half cycle, point X is positive with respect to point Y. This …
Reluctance Pulse Pick up Transducer: This Reluctance Pulse Pick up Transducer is very suitable for the measurement of shaft speed and liquid flow. It is based on the principle that if the field of any magnet is varied momentarily by the motion of an external magnetic body near it, a voltage pulse is generated at …
Frequency Generating Transducer: Frequency Generating Transducer – Unlike variable parameter analog transducers, frequency and pulse generating transducers measure physical variables in terms of a pulse repetition rate. Since frequency is an analog quantity, these can be treated as either analog or digital devices. Therefore, any phenomenon to be measured is converted into a corresponding rate …
Platinum Thin Film RTD Sensors: Platinum Thin Film RTD Sensors are manufactured by a very thin layer of platinum in suitable pattern to achieve smaller dimension and higher resistance, on a ceramic base. The deposition of layers and introduction of patterns are obtained using different methods. Normally, a number of such chips are manufactured on …
Phototransistor Construction and Working Principle: The sensitivity of a photo diode can be increased by as much as 100 times by adding a junction, resulting in an NPN device. A simple representation of the Phototransistor Construction is shown in Fig. 13.36. Illumination of the central region causes the release of electron hole pairs. This lowers …
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Photovoltaic Cell Working Principle and Types of Photovoltaic Cells: The Photovoltaic Cell Working Principle or solar cell, produces an electrical current when connected to a load. Both silicon (Si) and selenium (Se) types are known for these purposes. Multiple unit silicon photo-voltaic devices may be used for sensing light in applications such as reading punched …
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Resonance Bridge for Measurement of Inductance or Capacitance: One arm of this Resonance Bridge, shown in Fig. 11.29, consists of a series resonance circuit. The series resonance circuit is formed by Rd, Cd and Ld in series. All the other arms consist of resistors only. Using the equation for balance, we have Z1Z4 = Z2Z3, where …
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AC Wheatstone Bridge: Impedances at AF or RF are commonly determined by means of an ac Wheatstone bridge. The diagram of an ac bridge is given in Fig. 11.17. This bridge is similar to a dc bridge, except that the bridge arms are impedances. The bridge is excited by an ac source rather than dc …
Microprocessor Controlled Bridge: Microprocessor Controlled Bridge – Digital computers have been used in conjunction with test systems, bridges, and process controllers for several years. In these applications, computers were used to give instructions and perform operations on the data measured. When microprocessors were first developed they were used in much the same way as digital …