Discrete device states

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 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 ... 

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 ... 

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. 

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. 

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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