HoneywellControlEdge HC900 Controller Specifications 51-52-03-31, January 2022

Redundant Power - A second (backup) power module may 

be added to each ControlEdge HC900 controller rack. An 

extended rack is available that expands the standard 8 and 

12 I/O rack to accommodate a second (redundant) power 

supply and power status module.

Redundant Architectures

Redundant Controller

Two redundant C75 CPUs operate in a separately 

mounted controller rack, each with an independent 

900PS1 model power supply. A Redundant Switch 

Module (RSM) is located in the rack between the two 

C75 CPUs. A key switch on the RSM allows the user 

to change the operating mode of the Lead CPU. There 

is no I/O in the controller rack; the CPUs communicate 

with up to 12 racks of I/O over a 100 base-T Ethernet 

physical communication link or fiber optics with an 

external media converter for greater distance. When 

more than one I/O rack is used in the system, Ethernet 

switches are required, one port for each Scanner 

connection. In operation, all control functions and host 

communication exchanges are handled by the Lead 

controller, including configuration and operator 

changes. The Lead controller updates the Reserve 

controller every scan cycle with all the information 

needed to assume control in the event of a fault 

condition.

After power-up of the C75 CPUs, the first available 

CPU assumes the Lead function. The Lead may be 

transferred to the Reserve controller by:

• Failure of the Lead controller,

• Manually changing a keyed switch located on 

the Redundant Switch Module, 

• Input pin on Redundancy Status function block, or

• Instruction from host communication.

Dual Networks for Host communications are provided on the 

C75 CPU. Both network ports are continuously active on the 

Lead controller. Matrikon OPC server is available from 

Honeywell Matrikon to support dual Ethernet 

communications and automatically transfer communications.

The C75 network ports may otherwise be used in nonredundant mode where only one of the communication ports 

is used.

Remote I/O - To extend the distance between the CPU rack 

and the most distant I/O rack to 300m (984 ft.) up to two 

Ethernet switches may be used in each I/O connection. 

Distances up to 40km are possible with fiber optic cable.

Operator Interface – The 900 Control Station Operator 

Interfaces (900CR series) is supported with the C75 CPU.

An Ethernet connection is made to a switch connected to 

the Ethernet port of each CPU. The operator interface 

communication to the controller follows the Lead controller 

assignment.

Status/Diagnostics - An output parameter of the system 

monitor function block of C75 CPUs provides a digital status 

of the Reserve controller to allow integration of this 

information into the control strategy. C75 CPUs also provide 

diagnostic status on redundancy operation that may be 

observed using Designer configuration software. A 

Redundancy status function block is also available to 

monitor redundant controller operation. 

Function Blocks

A large assortment of analog and digital function 

blocks are available to solve the most demanding 

control requirements. Function blocks are grouped by 

scan rate, fast or normal, and by function, Principal or 

Standard.

Function Block Execution - All function blocks 

operate synchronously with I/O processing. Inputs are 

measured at the start of every scan and outputs are 

updated at the end of every scan. Function blocks 

such as Time Proportioning Outputs (TPO) and 

Position Proportioning outputs (PPO) require higher 

output resolution and are updated when the function 

blocks are executing. Micro-controllers on digital I/O 

modules can maintain TPO duty cycle operation during 

failsafe conditions. Micro-controllers on all I/O modules 

allow outputs to be configured to assume a default 

state in the event of a fault condition.

Normal Scan: Function blocks that execute during the 

Normal Scan are synchronized to the analog input 

measurements. The fastest update rate is 500ms. 

100ms analog capable from version v6.300 and above. 

Note: Low Level AI updates @ 0.5 sec.

Fast Scan: The fastest update rate for fast scan 

function blocks in a single controller rack is 10ms. The 

update rate starts at 25ms when remote racks are 

used and for redundant systems.

Principal Function Blocks – These function blocks 

are supported by dedicated Widget objects in Station 

Designer software for configuring 900 Control Station 

operator interfaces. They have Tag names and other 

attributes to support on-line user interaction. Principal 

function blocks can be used any number of times in a 

configuration.

Typical Principal function blocks include PID, Set Point 

Programming, Sequencers, Alternators, Stage, etc

Standard Function Blocks – The number of standard 

function blocks that may be used in a configuration is 

virtually unlimited. Typical Standard blocks include