发布时间 : 星期日 文章自动化制造系统与PLC论文中英文资料外文翻译文献更新完毕开始阅读048c487ab307e87101f696e8
the 24Vac power supply - this is like the positive terminal on a DC supply. Power is supplied to the left side of both of the switches. When the switches are open there is no voltage passed to the input card. If either of the switches are closed power will be supplied to the input card. In this case inputs 1 and 3 are used - notice that the inputs start at 0. The input card compares these voltages to the common. If the input voltage is within a given tolerance range the inputs will switch on. Ladder logic is shown in the figure for the inputs. Here it uses Allen Bradley notation for PLC-5 racks. At the top is the location of the input card I:013 which indicates that the card is an Input card in rack 01 in slot 3. The input number on the card is shown below the contact as 01 and 03.
Many beginners become confused about where connections are needed in the circuit above. The key word to remember is circuit, which means that there is a full loop that the voltage must be able to follow. In Figure 3.1 we can start following the circuit (loop) at the power supply. The path goes through the switches, through the input card, and back to the power supply where it flows back through to the start. In a full PLC implementation there will be many circuits that must each be complete. A second important concept is the common. Here the neutral on the power supply is the common, or reference voltage. In effect we have chosen this to be our 0V reference, and all other voltages are measured relative to it. If we had a second power supply, we would also need to connect the neutral so that both neutrals would be connected to the same common. Often common and ground will be confused. The common is a reference, or datum voltage that is used for 0V, but the ground is used to prevent shocks and damage to equipment. The ground is connected under a building to a metal pipe or grid in the ground. This is connected to the electrical system of a building, to the power outlets, where the metal cases of electrical equipment are connected. When power flows through the ground it is bad. Unfortunately many engineers, and manufacturers mix up ground and common. It is very common to find a power supply with the ground and common mislabeled.
One final concept that tends to trap beginners is that each input card is isolated. This means that if you have connected a common to only one card, then the other cards are not connected. When this happens the other cards will not work properly. You must connect a
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common for each of the output cards.
3.1.2.Output Modules
As with input modules, output modules rarely supply any power, but instead act as switches. External power supplies are connected to the output card and the card will switch the power on or off for each output. Typical output voltages are listed below, and roughly ordered by popularity. 120 Vac 24 Vdc 12-48 Vac 12-48 Vdc 5Vdc (TTL) 230 Vac
These cards typically have 8 to 16 outputs of the same type and can be purchased with different current ratings. A common choice when purchasing output cards is relays, transistors or triacs. Relays are the most flexible output devices. They are capable of switching both AC and DC outputs. But, they are slower (about 10ms switching is typical), they are bulkier, they cost more, and they will wear out after millions of cycles. Relay outputs are often called dry contacts. Transistors are limited to DC outputs, and Triacs are limited to AC outputs. Transistor and triac outputs are called switched outputs. Dry contacts - a separate relay is dedicated to each output.
This allows mixed voltages (AC or DC and voltage levels up to the maximum), as well as isolated outputs to protect other outputs and the PLC. Response times are often greater than 10ms. This method is the least sensitive to voltage variations and spikes. Switched outputs - a voltage is supplied to the PLC card, and the card switches it to different outputs using solid state circuitry (transistors, triacs, etc.) Triacs are well suited to AC devices requiring less than 1A. Transistor outputs use NPN or PNP transistors up to 1A typically. Their response time is well under 1ms.
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中文翻译
自动化制造系统与PLC
2．1介绍
控制工程随着时间的推移在不断发展。过去的人们主要致力于控制系统方面的研究。而最近电力已被应用于控制，早期电气控制是基于继电器的。这些继电器使其可以在没有机械开关的情况下被开启和关闭。使用继电器进行简单逻辑控制的方法很普遍。低成本计算机的发展带来了新一次的革命，可编程逻辑控制器（PLC）出现于十九世纪70年代，如今它已成为制造控制的最普遍选择。
PLC已逐渐在工厂车间中得到普及并很可能在未来的一段时间内占据主导地位。这一切都缘于PLC这些的优点：
1.能高效地控制复杂系统
2.应用灵活并能简单迅速地循环控制其他系统 3.强大的计算能力使其可以控制极其复杂的系统 4.故障排除帮助使编程更加容易，并可减少停机时间 5.可靠地组件使其有更长的使用寿命
2.1.1梯形逻辑
梯形逻辑是用于PLC的主要编程方法。正如之前所说，梯形逻辑已被用来模仿继电器逻辑。使用继电器逻辑图进行编程的决定是一个战略决策。通过选择梯形逻辑作为主要的编程方法，使培训工程师和商人所需要的资金极大的减少。
现代控制系统仍然包括继电器，但它很少用于逻辑。继电器是一个使用磁场来控制开关的简单设备，如图2.1。当电压作用于输入线圈产生磁场，磁场吸引金属开关使触点接触，则开关闭合。通电时闭合的触点称为常开触点，不通电时闭合的触点称为常闭触点。继电器通常在示意图中使用一个圆圈代表输入线圈，输出触点用两个平行线表示。常开触点用两根线表示并在输入端不通电时是开启（不导电）的，常闭触点用两根线和
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一个对角线穿过它们来表示，当输入线圈不通电时，常闭触点是闭合（导电）的。
输入线圈 或 常闭开关 常开开关 或
图2.1 简单的布局和继电器电路图
继电器用于是让一个电源控制关闭另一（通常是高电流）电源的开关，同时保持它们之间隔离。举一个用于简单控制的继电器的例子，如图2.2所示。在这个系统中，左边第一个继电器被用作常闭触点，并允许电流流过，直到输入端通电才断开。第二个继电器被用作常开触点，不允许电流通过，直到电压作用于输入端B。如果电流流过前两个继电器并通过继电器3中的线圈并闭合输出端C的开关。此电路通常被化成梯形图形式。这可以理解为如果A断开B闭合则C接通。
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