ABB AC 900F学习笔记73：Freelance_Mounting_and_Installation_AC_900F_Controller-33

继续学习

6.12.2 RS-485 Bus

RS-485总线

If the RS-485-bus is used, each connected bus line (each bus segment) must be electrically terminated. This includes：

如果使用RS-485总线，总线连接的每条线（每个总线段）必须被电气终止。这包括：

• one 120 Ohm bus terminating resistor on both wire ends, to avoid signal reflections.
• 在导线两端各有一个120欧姆的母线端子电阻，以避免信号反射。
• one additional 470 Ohm pull-up resistor on RxD/TxD-P and one 470 Ohm pull-down resistor on RxD/TxD-N per bus. These two resistors are designed to ensure a defined high level on the bus when no data are transmitted
• 每根总线上RxD/TxD-P上一个额外的470欧姆上拉电阻和RxD/TxD-N上一个470欧姆下拉电阻。这两个电阻的设计是为了确保在没有数据传输时总线上的定义高电平
• shielded twisted-pair cables with the characteristic impedance of 100 to 120 Ohm.
• 特性阻抗为100 ~ 120 ω的屏蔽双绞线。

Single controller

单控制器

The two 470 Ohm resistors are integrated into the CPU module and can be activated by a short wire link between the terminals 1-2 and 3-4. The following drawing shows an RS485 bus with a bus master at the line end.

CPU模板内部集成了两个470欧姆的电阻，能够通过短接终端1-2和短接终端3-4激活。下图展示了在线末端RS485总线为主的情形。

If the master is located within the bus line, a terminating resistor is not provided. The pull-up resistor and the pull-down resistor, however, need to be activated (see drawing below). The cable shields of the bus line must be earthed.

如果主站位于总线内，不提供终端电阻。上拉电阻和下拉电阻需要被激活（见下图）。总线电缆的屏蔽层需要接地。

上图中，中间的RS-485主站就没有使用终端电阻，两头的使用了电阻。

The external 120 ohm resistor (line termination) must be protected against electrostatic discharge. It is recommended to provide the complete resistor (except for the wire ends) with a heat shrink tube for this purpose. 外部120欧姆电阻(线路终端)必须防止静电放电。建议提供一个完整的带热缩管的电阻器(除了线端)达到此目的。

 

Redundant controller

冗余控制器

The RS-485 bus lines of a redundant controller should first be connected to terminal strips and then be guided to the field. The terminal strips must be arranged as close as possible to the controller. In this configuration, the pull up/down resistors of the CPU module are not required. The bus is terminated exclusively by external resistors.

冗余控制器的RS-485总线应线连接到终端端子，然后再接到现场（设备）。终端端子必须尽可能靠近控制器紧密排列。这种情况下，控制器的上拉下拉电阻不再需要。总线通过外部电阻终止。

A regulated power supply with output voltage 5 V DC +/- 10% is needed to provide for a defined quiescent level on the RS-485 bus

需要一个输出电压范围5V DC±10%的电源为RS-485总线上的静态电平提供电压。

The 5 V DC power supply unit must have a safe electrical isolation. For external resistors the same requirements apply as for those of a single controller. 5v DC电源单元必须具有安全的电气隔离。对于外部电阻的要求与单控制器的要求相同。