Synchronous Modulation and Demodulation: Synchronous Modulation and Demodulation – Low dc current may be transformed into a high voltage dc by simple chopper action. Although an inductive type transformation process is required, the out­put dc may be obtained without rectifying devices. Figure 14.39 shows a circuit function of a synchronous vibrator. Contacts a and b […]

Varactor Diode Symbol: A specially processed junction diode that assumes the properties of a variable capacitor (about 5 —250 pf) when its dc reverse voltage is varied is called a Varactor Diode Symbol shown in Fig. 14.37. This unique behaviour can be used in special modulator circuits designed to turn a low voltage dc signal […]

Transistor Chopper Circuit: Transistor Chopper Circuit – A single transistor used as a dynamic switch to convert low level dc signal to an ac waveform is shown in Fig. 14.34. If the voltage applied to the tran­sistor base is negative (in the case of a PNP transistor), both emitter and collector diodes are shorted, and […]

Diode Bridge Type Modulator: Diode Bridge Type Modulator – Figure 14.33 shows a silicon diode ring modulator with an associated ac coupled dc amplifier. The amplifier itself has a gain of 65 db and a flat response within ± 1 db, from 8 Hz to 80 kHz. Precautions are taken to safeguard the amplifier against […]

Magnetic Modulator: Magnetic Modulator – The most reliable substitutes for electromechanical choppers are magnetic modulators. These devices reach a null stability as low as 10 μV, but their response time is often less than 2 Hz and the ambient temperature range is restricted. The 3-leg saturable reactor, shown in Fig. 14.32 falls within the cat­egory […]

Self Oscillating Converter(Transistorised Chopper Circuit): A Self Oscillating Converter(Transistorised Chopper Circuit) dc to ac converter suitable for low level dc signal is illustrated in Fig. 14.30. The unique property of this assembly is that it starts to oscillate vigorously at very low levels of dc collector voltages at only a few micro-watts of collector power. […]

Electromechanical Chopper: Electromechanical Chopper – An ac amplifier must see ac in order to perform useful work. A fair number of chopping and modulation techniques are available to change direct current, or to change very slowly varying signals into square waves (or pulses). Associated circuitry, inserted at the amplification system common output, may then be […]

Chopper Type DC Amplifier Transformer: A simple Chopper Type DC Amplifier Transformer may be used to amplify a dc input through the use of additional circuit component known as chopper. In this circuit, the dc signal is first converted into an ac signal, amplified by a standard amplifier, and finally converted back to a dc […]

Differential Instrumentation Amplifier Transducer Bridge: Figure 14.25 shows a simplified circuit of a Differential Instrumentation Amplifier Transducer Bridge. In this circuit a resistive transducer (whose resistance changes as a function of some physical energy) is connected to one arm of the bridge. Let RT be the resistance of the transducer and ΔR the change in […]

Instrumentation System: Instrumentation System – The measurement and control of physical conditions is very important in many industrial and consumer applications. For example, the operator may make necessary adjustments in the measurement of temperature or humidity inside a dairy or meat plant to maintain the product quality, or to produce a particular type of plastic, […]