Discrete devices

Discrete Device States Discrete devices such as two-position valves can be driven to either of two possible states. Such devices can be optionally outfitted with limit switches that indicate the state of the device. For two-position valves, the following combinations are possible ... 

For each process state, the various discrete devices are expected to be in a specified device state. For process state Transfer from A, the device states might be as follows ... 

For many batch processes, process state representations are a very convenient mechanism for representing the batch logic. A grid or table can be construc ted, with the process states as rows and the discrete device states as columns (or vice versa). For each process state, the state of eveiy discrete device is specified to be one of the following ... 

Many batch software packages also recognize process states. A configuration tool is provided to define a process state. With such a mechanism, the batch logic does not need to drive individual devices but can simply command that the desired process state be achieved. The system software then drives the discrete devices to the device states required for the target process state. This normally includes the following ... 

Should any discrete device not remain in its target state, failure logic must be initiated. 

The start of the solid-state electronic industry is generally recognized as 1947 when Bardeen, Brattain, and Shockley of Bell Telephone Laboratories demonstrated the transistor function with alloyed germanium. The first silicon transistor was introduced in 1954 by Texas Instruments and, in 1956, Bell Laboratories produced the first diffused junction obtained by doping. The first-solid state transistor diodes and resistors had a single electrical function and were (and still are) known as discrete devices. 

Many of these steps include CVD, and CVD is now a major process in the fabrication of monolithic integrated circuits (IC), custom and semi-custom ASIC s, active discrete devices, transistors, diodes, passive devices and networks, hybrid IC s, opto-elec-tronic devices, energy-conversion devices, and microwave devices. 

Electronic devices are either discrete devices or integrated circuits (IC s). Discrete devices perform a single function and include the following ... 

Continuing to monitor the state of each device to ensure that the devices remain in their proper states. Should any discrete device not remain in its target state, failure logic must be initiated. 

Discrete devices can, of course, be connected in arrays to obtain better selectivity or higher accuracy. Devices fabricated concurrently may have more similar characteristics than discrete devices made at different times, and so be better suited for use in arrays. 

Figure 2.4. Commercial discrete devices for chemical reactions assisted by ultrasound probes. (A) Rosett cell, (B) indented cell, (C) Suslick cell and (D) cup horn.

The modern electronics era began at Bell Telephone Laboratories in 1948 with the invention of the solid-state transistor, which replaced the large thermionic vacuum tube, the mainstay of the electronics industry for the previous 40 years. Transistors were smaller and much more robust than their vacuum tube counterparts and required much less power to operate. Electronic circuits of the 1950s and early 1960s were assembled from discrete transistors, diodes, and resistors, for example, but rapid advances in circuit complexity and density, driven by developments in computer technology, soon led to an impasse, namely, how to approach the problem of interconnecting hundreds, perhaps thousands, (some visionaries would have said millions) of discrete devices into a complex circuit. 

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