Product Overview of the Allen-Bradley 1785-L26B

The Allen-Bradley 1785-L26B is a trusted PLC-5 series standard processor. Specifically, it belongs to the powerful PLC-5/26 family of controllers. This processor efficiently manages inputs and outputs from field devices. Therefore, it serves as the brain of your automation system. The 1785-L26B also provides protected memory for critical control programs. Furthermore, it uses battery-backed SRAM to retain data during power loss.

Processor Memory and I/O Capacity

First, let us examine the memory specifications. The 1785-L26B offers 16 Kilowords of maximum user memory. In addition, it supports a maximum total I/O of 512 in any mix. You can also configure 512 inputs and 512 outputs in a complementary setup. As a result, this processor handles complex control tasks easily. The 1785-L26B also manages up to 512 analog I/O channels. Consequently, it works well for both digital and analog applications. This processor supports a maximum of 13 I/O chassis in total. Moreover, remote I/O chassis can reach up to 12 units.

Communication and Scan Performance

The I/O scan time varies directly with communication speed. For example, at 57.6 kbits/s, each rack scans in 10 ms. Similarly, at 115.2 kbits/s, the scan time drops to 7 ms. Finally, at 230.4 mbits/s, you achieve a fast 3 ms scan time. The 1785-L26B draws a maximum backplane current of 2.6 amps at 5 Volts DC. Therefore, ensure your power supply can handle this load.

This processor includes one RS-232-C/422-A/423-A serial port. Additionally, it has a Control Coprocessor Expansion Port. A DH+ (Data Highway Plus) port connects to the DH+ network. Likewise, a Remote I/O port (Channel 1B) handles remote connections. The 1785-L26B uses a 25-pin D-shell connector for serial communication.

Addressing Modes and Module Compatibility

The 1785-L26B supports three flexible hardware addressing modes. First, the 2-slot addressing works with any mix of 8-point modules. You can also use a pair of 16-point modules in this mode. However, no 32-point module works with 2-slot addressing. Second, the 1-slot addressing accepts any mix of 8-point or 16-point modules. You can also use a pair of 32-point modules here. Third, the half-slot mode works with any mix of 8, 16, and 32-point modules. Thus, you can optimize chassis space efficiently.

This processor works with most 1771 I/O modules. Furthermore, it supports 1794 I/O, 1746 I/O, and 1791 I/O modules. Both 8-point, 16-point, and 32-point modules are compatible. Intelligent I/O modules also work with the 1785-L26B. The controller supports the 1785-RC relay cartridge as well. This cartridge provides an interface for all external devices. Therefore, the 1785-L26B offers remarkable flexibility.

Environmental, Electrical, and Physical Attributes

You can operate the 1785-L26B between 0 to 60 °C (32 to 140 °F) . Additionally, the ambient humidity range is 5-95% without condensation. This processor withstands an operational shock of 30G. Likewise, it tolerates vibration of 1G at 10-500 Hertz. The 1785-L26B comes in an open-style enclosure. However, you must install it inside a suitable cabinet for protection.

The processor offers excellent voltage isolation between communication ports. Testing occurs at 500 Volts for 1 minute between ports. Similarly, isolation between the communication port and relay cartridge is 1000 Volts for 1 minute. The 1785-L26B weighs approximately 1.42 kilograms (3 pounds) . Finally, it holds UL, CE, CSA, and C-TICK certifications.

Installation Guidelines for the 1785-L26B

First, install the 1785-L26B in the left-most slot of the 1771 I/O chassis. This position ensures proper backplane communication. Always disconnect power before inserting or removing the processor. The module draws 2.6 amps from the 5V DC backplane supply. Therefore, verify your power supply capacity beforehand. Use proper grounding techniques to avoid electrical noise. The 1785-L26B also requires a clean and dry environment within the temperature range.

For battery-backed SRAM operation, check the battery status regularly. A low battery can cause program loss during power down. Thus, schedule periodic battery replacements. The 1785-L26B supports EEPROM backup using 1785-ME16, -ME32, -ME64, or -M100 modules. Consequently, this backup protects your program without battery dependency. Finally, always verify your addressing mode before installing I/O modules.

Status Indicators and Diagnostics

The front panel of the 1785-L26B includes several useful status LEDs. These indicators show processor and communication status at a glance. For instance, you can quickly identify running, fault, or battery conditions. The DH+ port LED shows network activity clearly. Similarly, the Remote I/O port LED indicates remote chassis communication. The processor LED shows run or program mode status. Therefore, troubleshooting becomes much faster with these indicators.

Package Contents

• One Allen-Bradley 1785-L26B PLC-5/26 Standard Processor

• One user manual with installation instructions

• One battery for SRAM backup (pre-installed)

• One set of connector covers for unused ports

Frequently Asked Questions (FAQ)