OR gates

The most accurate flow rate control can be achieved by using the loss-in-weight method. The total amount of material required for a downstream process is first added to a tank or hopper scale. As the material is discharged, the loss-in-weight is monitored and used to modulate the discharge valve or gate to achieve the desired flow rate. 

These two events are related to each other through an OR gate, ie, the top event can occur if either road debris or tire failure occurs. Another type of gate is the AND gate, where the output occurs if and only if both inputs occur. OR gates are much more common in fault trees than AND gates, ie, most failures are related in OR gate fashion. 

An example of a faiilt tree logic diagram using AND and OR gate logic is shown in Fig. 26-5. 

To control this loss one typically attempts to minimize the voltage drop across the power switch during its on-time. To do this, the designer must operate the switch in a saturated state. These conditions are given in Equations 4.2a and b. This is identified by overdriving the base or gate such that the collector or drain current is controlled by the external elements and not by the power switch itself. 

Initially, a system s hierarchy is identified for subsystems, sub-subsystems and so on to the components for which data must be found. The top event specifies system failure subsystems required for operation of the system in the mode specified are input to the top event s OR gate. Redundancy is represented by the redundant systems inputting an AND gate. This process of grouping subsystems under OR gates, if they can individually fail a function, or under AND gates if concurrent failures are necessary, is continued to the component or support system level until the tree is completed. This process grades the hierarchy from top to bottom, down the fault tree. 

Using de Morgan s theorem (Table 2.1-1), the fault tree in Figure 3.4.4-9 is converted into the success tree shown in Figure 3.4.4-10. Notice that the effect of the theorem is to reverse tlie logic "AND" gates become "OR" gates and vice versa failure becomes success and vice versa. 

The AND gate is a vertical bar with inputs as arrows the OR gate is a circle with anows at angular incidence. 

MOCUS implemented the Fussell algorithm (Fussell, 1974) for top-down solutions of the fault tree. This algorithm was used in ALLCUT and was modified to be bottom-up in WAMCE T. While cutsets are valuable for qualitative and quantitative purposes, they are not compact. They are thousands of trains (AND sequences) connected to one OR gate. 

Remove Unused - deletes all unused basic events or gates. 

The overall frequency of the top event is calculated by combining together the constituent probabilities and frequencies of the various events in the fault tree using the appropriate logical relationships described by the AND and OR gates (the detailed calculation is given in CCPS, 1989b). 

Consider the following fault tree for a flammable storage tank fire. Identify whether the numbered boxes are (and) or (or) gates. 

For Excess Flammable Vapor to occur, a Large Leak in Flammable Contiiiners or Inadequate Ventilation must be present. Therefore, box 2 is an or gate since only one situation need occur. 

The alternate concept which has been in use for many years is to fabricate or purchase a Tee connection upon w hich the two safety relief valves can be mounted on top of their full-port plug or gate valve with required locking lugs. 

It was mentioned above that in order for the AND gate shown in figure 3.82-b to operate properly, the gliders in input A must be delayed by a time equal to the distance between the two annihilation reactions. The same is true of the operation of the OR gate, shown in figure 3.82-c. 

Fig. 3.82 Schematic representations of NOT, AND aiid OR gates E = eater (see figure 3.76), G = glider-gun (see figure 3.79) and T = thin glider-gun (see figure 3.81).

Fig. 6.5 Schematic representations and truth tables for conventional AND and OR gates. Observe that both gates dissipate energy if the output of the AND gate equals 0 (or the output of the OR gate equals 1 ), there is no way of deducing the values of the respective inputs.

Von Neumann was able to construct a self-reproducing UTM embedded within a 29-state/5-cell neighborhood two-dimensional cellular automaton, composed of several tens of thousands of cells. It was, to say the least, an enormously complex machine . Its set of 29 states consist largely of various logical building blocks (AND and OR gates, for example), several types of transmission lines, data encoders and recorders, clocks, etc. Von Neumann was unfortunately unable to finish the proof that his machine was a UTM before his death, but the proof was later completed and published by Arthur Burks [vonN66]. 

These cutting operations are usually used only for machined prototypes, or very low volume production of simple shapes. High speed routing is sometimes used for slotting or gate removal on injection molded products. Standard end mills (two-flute), cir-... 

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