Voltage-controlled device

For low-power applications, the devices of choice are the MOSFET, the IGBT, and the BJT. For applications up to 1 kV, the MOSFET is the device of choice because it is a voltage-control device and has a fast switching speed. For applications ranging in voltage from 1 kV up to 4 kV, the IGBT is most often used. The thyristor and the GTO are used for voltages over 4 kV. 

Tacho generator (TG) - This is an analogue voltage feedback device and can provide a speed input to the inverter control circuit. It provides only a low level of speed regulation, typically x 0.4% of the set speed. 

Tandem MS has been more or less successfully performed with a wide variety of analyzer combinations. What analyzers to combine for a certain application is determined by many different factors, such as sensitivity, selectivity, and speed, but also size, cost, and availability. The two major categories of tandem MS methods are tandem-in-space and tandem-in-time, but there are also hybrids where tandem-in-time analyzers are coupled in space or with tandem-in-space analyzers. Moreover, the ongoing development of faster electronics and high-voltage circuits as well as better software tools and hardware control devices constandy open up new possibilities of making innovative combinations of analyzers for specific applications. In this chapter a few examples of commercially available tandem MS instruments are presented. A brief summary of their weaknesses, strengths, and main areas of applications is given. 

Figure 11.10. Phase-locked detection of fluorescence lifetime using single reference signal. FID = fluorescence inducing and detecting devices LPF = low-pass electronic filter VCO = voltage-controlled oscillator v, = signal to modulate the output intensity of the excitation light source v/= the fluorescence signal.

In PSpice both a 7414 and a CD4093 were used. The 7414 is the digital model for the Schmitt trigger inverter. To use the digital device for an analog measurement, E sources (voltage-controlled voltage sources) were used as buffers. The schematic used for the PSpice model is shown in Fig. 8.59. The results are displayed in Fig. 8.60. 

---