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Hardware Comparison: GE RX3i vs Allen-Bradley ControlLogix

The GE PLC product line has a long history of innovation within the power and energy industry. GE PLC systems are largely implemented in emergency power supply systems, due to their high performance in mission critical power, making it a reliable choice also in various industry scenarios. For this article we will focus on the RX3i Series.

The Allen Bradley controllers are considered the most popular programmable logic in the US, due to their easy programming and debugging features. The ControlLogix series is classified as a large control system which is typically used in plant-wide applications.



Both solutions are modular, suitable for high-performance, discrete and motion applications, in harsh environments if needed, with a baseplate system to accommodate a wide range of modules covering digital, analog, and numerous other specialty I/O types, embedded or remotely distributed.

The RX3i Universal baseplates support hot swap capability to reduce downtime while the Armor option of ControlLogix enables on-machine mounting due to its IP67 rate.


Comparing the top CPU offers from both systems, ControlLogix 5580 and RX3i CPU320, both support high-availability, GE using a 1GHz CPU with 64Mb internal memory and Allen Bradley’s controller reaching up to 40Mb internal memory while assuring 32 simultaneous tasks with 1000 programs per task and no limit for local I/O event triggers.


Regardless of the I/O mix chosen, these systems can be scaled up by adding modules, locally or remotely. RX3i can support up to 32 000 I/O points per system and ControlLogix can manage up to 128 000 points.

Below is a list of I/O available for each controller, both brands offering a wide range of options, and some specialty modules:


  • Digital (Voltage / TTL / Relay)
  • Analog (Voltage / Current / RTD / Thermocouple / HART)
  • Specialty Modules
  • Pulse Test (24, 125 VDC)
  • High Speed Counters
  • Pulse With Modulation (PWM)
  • Pulse Output
  • Power Sync & Measure
  • Strain Gauge
  • SoE Inputs (application)

Allen Bradley ControlLogix

  • Digital  (Voltage / Isolated and non-isolated)
  • Analog  (Voltage / RTD / Thermocouple / Isolated and non-isolated / HART)
  • Specialty Modules
  • Configurable flowmeter
  • High-speed counter
  • Programmable limit switch


GE RX3i provides various network interfaces (PROFINET, ModBus/TCP, EtherNet, CMX, PROFIBUS DP) and also several Gateways for communicating with third party applications (Serial, Modbus, HART, GENIUS, DNP3 Seral/TCP, IEC-61850, IEC-104, PROFIBUS /Master, CANOpen).

ControlLogix offers networking in EtherNet/IP, ControlNet, DeviceNet and PROFIBUS DP and also communicates with third party equipments by EtherNet/IP, Serial DF1, Modbus and DLR.

Within all these options it is possible in either systems to have network and system redundancy as well as I/O redundancy via application code (GE) or additional module (Allen Bradley).


GE RX3i offers an upgrade plan from legacy systems like Series 90-30, 90-70, and RX7i. RX3i allows to re-use Series 90-30 modules on RX3i baseplates, so it is possible to upgrade the I/O system without disturbing wires or buying new I/O modules. Upgrading to RX3i provides improved communications with integrated Ethernet along with USB and serial connections or memory sticks.

Allen-Bradley as a reputation for its high reliability and maintainability. This brand is known for their backward compatibility and legacy support, also supporting a migration path from previous generations of PLC.

When new hardware features are integrated, software is upgraded to support all those features. If a new processor with more memory comes out, software will be up-to-date to support additional memory.


Both systems are suitable for harsh and high demand environments, including production equipment, being efficient enough to enable the operator to work closer to the process without compromising operator safety. This is possible due to the possibility of TUV-certified SIL3 machine safety capabilities.

By combining secure network connectivity and certified safety function it is possible to integrate standards compliant safety capabilities to the equipment while meeting increasingly stringent regulatory requirements.

This is achieved in Allen Bradley with the addition of a GuardLogix Safety Controller and in GE with a VersaSafe module communicating by PROFINET with the master CPU.

Motion and Motor Control

Both series have motion control modules that can be used for a wide range of applications.

The RX3i IC694APU300 features 1Mhz input frequency, expanded filtering, single ended, differential encoders, 32 bit counters, Z counter and windowing. The IC695HSC308 features high speed I/O processing, 8 counters, supports high speed counting, PLS (programmable limit switch), camming, input interrupts and pulse width timing.

GE also has a solution for wider motion applications, from small material handling applications to complex multi-axis machines and electronic line shaft applications, with the PACMotion controller, which is a versatile 4-axis servo motion controller that provides more scalability and flexibility. PACMotion provides real-time synchronization of all axes in an RX3i rack. A separate RX3i fast logic scan enables fast deterministic event response and synchronization, and the demand driven data exchange model between the RX3i CPU and PACMotion module many significantly reduce scan time impact. The 4-axis servo motion controller is built on a high performance hardware platform, with a new enhanced motion engine, operating system, and open standard integrated programming paradigm

Allen Bradley has an extensive portfolio from fixed speed starters, through variable frequency drives for a wide range of applications, to high-performance, multi-axis servo drives for the most demanding applications, including rotary and linear servo motors, safety servo drives to minimize downtime and reduce energy and production waste, linear actuators and stages for flexible servo control, absolute encoders for closed-loop control systems and incremental optical encoders that provide low cost, small size, high frequency and high resolution control.

The ControlLogix series also includes specific motor control modules, PowerFlex AC Drives and PowerFlex Medium Voltage Drives that enable enable soft-starting and variable-speed control of processes with high-power demands thus helping to reduce energy costs, component count, maintenance and motor wear. For more heavy duty applications, there’s also available CENTERLINE Motor Control Centers (MCCs) that offer a rugged, high-performance packaging solution. Motor Control SMC™ soft starters can also be integrated into an intelligent motor control solution to offer higher productivity and shorter downtimes.

Additional Features GE

RX3i Pneumatic Module

This output module provides 11 pneumatic outputs and five 24 VDC sourcing outputs. For each pneumatic output, the module contains an internal 3-way solenoid-actuated valve and an associated output fitting. Solenoid power is supplied from an external 24 VDC source to the “DC Outputs” connector on the front panel.

Additional Features AB

Condition and Energy Monitoring modules

Configured from Studio 5000 for CompactLogix or ControlLogix controllers with v24+ or V20 firmware, allows machinery protection to API-670 5th Edition. These modules are powered using single or redundant 18-32V DC SELV supplies and are suitable for environments from -25 to 70 °C, including hazardous area (certifications – IECEx Conformity; ATEX Zone 2; UL Class 1 Div 2; Groups A, B, C, D). The modules have spring or screw style removable plug connectors and circuit cards are conformal coated.

Final Considerations

From a user / programmer point of view, GE is a very powerful and reliable platform, but some consider the ladder editor somewhat dated. The ladder editor itself really hasn’t changed since the DOS days of Logicmaster, the programming software has been updated, and is useful yet the ladder editor is dated. But there is an advantage to this architecture, it is possible to import VersaPro and Logicmaster files into the current programming software (Cimplicity Machine Edition or Proficy Machine Edition), which makes upgrading older software to new software very easy.

Allen Bradley’s Studio 5000 software combines engineering and design elements into one standard framework that enables PLC and user interface programming in just one tool thus optimizing commissioning time, offering emulation and simulation functions that allow for test and debug without ever interfering the physical hardware.

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This entry was posted on November 9th, 2020 and is filed under Allen-Bradley, Automation, GE Fanuc, Hardware Comparison, Technology. Both comments and pings are currently closed.

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