标题: ISA5.2Use of symbols [打印本页] 作者: 学习自控仪表 时间: 2016-12-20 17:42 标题: ISA5.2Use of symbols By using the symbols designated as "basic," logic systems may be described with the use of only the most fundamental logic building blocks. The remaining symbols, not basic, are more comprehensive and enable logic systems to be diagrammed more concisely. Use of the non-basic symbols is optional.
A logic diagram may be more or less detailed depending on its intended use. The amount of detail in a logic diagram depends on the degree of refinement of the logic and on whether auxiliary, essentially non-logic, information is included.
As an example of refinement of detail: A logic system may have two opposing inputs, e.g., a command to open and a command to close, which do not normally exist simultaneously; the logic diagram may or may not go so far as to specify the outcome if both the commands were to exist at the same time. In addition, explanatory notes may be added to the diagram to record the logic rationale.
Non-logic information may also be added, if desired, e.g., reference document identification, tag numbers, terminal markings, etc.
In these ways, the diagram may provide the level of detail appropriate, for example, for communication between a designer of pneumatic circuits and a designer of electric circuits, or may provide a broad-view system-description for a plant manager.
The existence of a logic signal may correspond physically to either the existence or the nonexistence of an instrument signal, depending on the particular type of hardware system and the circuit design philosophy that are selected.* For example, a high-flow alarm may be chosen to be actuated by an electric switch whose contacts open on high flow; on the other hand, the high-flow alarm may be designed to be actuated by an electric switch whose contacts close on high flow. Thus, the high-flow condition may be represented physically by the absence of an electric signal or by the presence of the electric signal. The Standard does not attempt to relate the logic signal to an instrument signal of any specific kind.
It is recommended, for clarity, that a single time-function symbol, as appropriate, be used to represent each time function in its entirety. Though not incorrect, the representation of a complex or uncommon time function by using a time-function symbol in immediate sequence with a second time-function symbol or with a NOT symbol should be avoided (see Section 4.8).
By using the symbols designated as "basic," logic systems may be described with the use of only the most fundamental logic building blocks. The remaining symbols, not basic, are more comprehensive and enable logic systems to be diagrammed more concisely. Use of the non-basic symbols is optional.
通过使用被指定为“基本”的符号，可以仅使用最基本的逻辑构建块来描述逻辑系统。剩下的那些非基本符号作为补充可使逻辑系统能够更简洁明了。当然非基本符号是可选的。
A logic diagram may be more or less detailed depending on its intended use. The amount of detail in a logic diagram depends on the degree of refinement of the logic and on whether auxiliary, essentially non-logic, information is included.
逻辑图的复杂程度取决于其预期用途。逻辑图中的细节量取决于逻辑的细化程度以及是否包括辅助的，本质上非逻辑的信息。
As an example of refinement of detail: A logic system may have two opposing inputs, e.g., a command to open and a command to close, which do not normally exist simultaneously; the logic diagram may or may not go so far as to specify the outcome if both the commands were to exist at the same time. In addition, explanatory notes may be added to the diagram to record the logic rationale.
作为细节改进的示例：逻辑系统可以具有两个相反的输入，例如，通常不同时存在的打开命令和关闭命令; 如果两个命令同时存在，则逻辑图的输出不一定符合预期。此外，可以向图中添加注释以记录逻辑架构，便于以后阅读和理解。
Non-logic information may also be added, if desired, e.g., reference document identification, tag numbers, terminal markings, etc.
必要的话也可以添加非逻辑的助记信息，例如：参考文献标识，标签号码、终端标志，等等。
In these ways, the diagram may provide the level of detail appropriate, for example, for communication between a designer of pneumatic circuits and a designer of electric circuits, or may provide a broad-view system-description for a plant manager.
通过这些方式，逻辑图可以以适当的方式来体现细节。如气动电气回路设计者与电路设计者的沟通，也可以体现工厂经理的宏观规划。
The existence of a logic signal may correspond physically to either the existence or the nonexistence of an instrument signal, depending on the particular type of hardware system and the circuit design philosophy that are selected.* For example, a high-flow alarm may be chosen to be actuated by an electric switch whose contacts open on high flow; on the other hand, the high-flow alarm may be designed to be actuated by an electric switch whose contacts close on high flow. Thus, the high-flow condition may be represented physically by the absence of an electric signal or by the presence of the electric signal. The Standard does not attempt to relate the logic signal to an instrument signal of any specific kind.
根据硬件系统的特性和电路设计需要，每一个逻辑信号对应者物理上存在的或不存在的仪表信号。*例如，一个高流量报警信号可能由流量开关在高流量时的断开动作产生，另一方面，也可以由流量开关的闭合动作产生。因此，得电和失电都可以表示高流量信号。标准并不试图将逻辑信号与任何特定种类的仪器信号相关联.
It is recommended, for clarity, that a single time-function symbol, as appropriate, be used to represent each time function in its entirety. Though not incorrect, the representation of a complex or uncommon time function by using a time-function symbol in immediate sequence with a second time-function symbol or with a NOT symbol should be avoided (see Section 4.8).
清楚起见，建议使用单时间函数符号来表示整个函数中的每个时间函数。虽然不是不正确，但表示一个复杂的或不寻常的时间函数时应尽量避免使用与二次时间函数符号或非符号立即序列相关的时间功能符号（见第4.8节）。