ABB AC 800M Complete Guide

Redundancy: 84 modules

Scanning cycle: Depending on the number of modules and bus load, it can be adjusted between 0 and 100 ms. Optimize the "Modulus Scan Time" parameter of Control Builder to a minimum of 10 ms. If an I/O communication timeout alarm occurs, gradually increase until stable.

5.2 PROFIBUS Remote I/O

Through the CI854 module, up to 99 I/O stations can be connected (including up to 62 redundant stations), with a maximum of 24 modules per station (12 redundant pairs). Unlike local Modulabus, the scanning cycle of PROFIBUS is greatly affected by the bus speed. In practical engineering, if there are more than 30 sites, it is recommended to set the speed to 500 kbit/s or lower and use active terminators.

Troubleshooting of power and environmental adaptability faults

6.1 Power Requirements and Common Power Supply Faults

All AC 800M CPUs require 24V DC (19.2-30V) with ripple ≤ 5%. Typical power consumption of each CPU:

PM851A/856A/860A：4.32 W

PM857/858：5.1 W

PM891：15.8 W

Fault phenomenon: CPU restarts frequently or the "Power Fail" indicator light flashes.

Troubleshooting steps:

Measure the voltage of the CPU power terminal, and if it is below 19V, check the voltage drop of the power supply circuit.

Measure the ripple using an oscilloscope. If the peak value exceeds 1.2V, parallel a 2200 μ F capacitor at the CPU terminal or replace the power module with SD831 (24V/5A).

Check the redundant power supply status input SA/SB: High level should be>15V, low level should be<8V. If the status detection is incorrect, it may be due to a damaged voltage divider resistor.

6.2 Temperature and Corrosion Protection

The working temperature of AC 800M is+5~55 ° C, and the storage temperature is -40~70 ° C. In high temperature environments (such as boiler rooms), it is necessary to ensure that the cabinet is ventilated and the IP20 protection level is not damaged. If a "Temp Over" alarm occurs, the following measures can be taken:

Add cabinet fans (recommended ebmpapst 4650N).

Install the CPU at intervals with high heat generating I/O modules (such as S800 analog output).

This series of controllers meets the G3 corrosion resistance level (ISA 71.04) and is suitable for light corrosive environments such as hydrogen sulfide and chlorine gas. If used in a chemical plant, check the coating for discoloration once a year and clean the gold fingers with anhydrous alcohol.

Shutdown module replacement strategy and hardware upgrade path

Although the document does not explicitly list discontinued models, according to the ABB product lifecycle, old models such as PM851A, PM856A, and PM858 have gradually been phased out of the market. The following are recommended replacement options:

7.1 Non redundant low-end replacement

Original PM851A → PM856A (same performance) or directly upgrade to PM861A (to obtain redundancy and higher memory).

Note: PM851A does not have Flash storage applications and requires battery backup; After replacement, the program needs to be ported to the new CPU and the I/O mapping needs to be recompiled.

7.2 Redundant System Replacement

Original PM858 (33 MHz, 16 MB RAM) → PM862 (67 MHz, 32 MB RAM) or PM866A (133 MHz, 64 MB RAM).

The performance improvement is significant, but it should be noted that PM858 uses MPC866, while PM862 is also MPC866, and the program can be directly ported. However, the UL 508 certification of PM858 is still valid on PM862, while PM866A does not have this certification. Caution should be exercised if used in the North American market.

Original PM860A → PM861A: Although PM860A does not support redundancy, if redundancy is required after replacement, a second PM861A can be purchased.

7.3 Replacement of Safety Controller

Original PM863 (96 MHz, 32 MB) → PM865 (same performance, but PM865 is a higher version) or PM867 (133 MHz, 64 MB).

All safety controllers must maintain SIL3 level and undergo safety verification again after replacement (such as FMEDA analysis). Note that PM863 does not have Flash storage, while PM865/PM867 have Flash, and the program loading method is different.

7.4 Communication module replacement

CI854A (Classic) → CI854B: CI854B supports module redundancy and adds diagnostic functionality. When replacing, it is necessary to update the GSD file and adjust the module types in the hardware configuration.

CI871 → CI871A: CI871A adds partial support for IRT (equal time synchronization) with lower power consumption (160 mA vs 190 mA). Replace directly without modifying the program.

Firmware upgrade and backup battery maintenance

8.1 Firmware upgrade steps

The firmware of AC 800M CPU is stored in Flash PROM (2 MB for PM851A/856A/860A/861A/864A; 4 MB for PM862/866A; 16 MB for PM891). Upgrading requires the use of Control Builder or CompactFlash Tool (PM891). Note:

Backup the application before upgrading (export as. apx or. xml).

For redundant systems, upgrade the backup CPU first, manually switch, and then upgrade the original main CPU.

During the upgrade process, it is absolutely forbidden to power off, otherwise the CPU may become bricked. If it occurs, it needs to be restored through the JTAG interface (TK212A tool cable).