Group3 Control - Overview
Typical installation of a Group3 control systemGroup3 Control is a fibre optically linked distributed control system. Data is sent over fibre optic cables to small intelligent outstations (Device Interfaces or DIs) that contain the I/O boards - ADCs, DACs, digital, motor drivers, etc.
A Loop Controller (or LC) card plugs into the control computer and handles all the communications on the fibre loop.
To read inputs and set outputs the control computer merely reads and writes to a Dual Port RAM on the LC. The microprocessor on the LC then lifts this information, packages it appropriately and sends it out on the loop.
Within each DI is a processor that decodes the information in the message packet and sets outputs accordingly, repacks the message with any input information and sends it back on the loop. The LC in the control computer then unpacks the input information and puts it in the Dual Port RAM, from where the control program can get the value of the inputs. In this manner information is transmitted over the loop at up to 1.152 Mbaud, continually refreshing outputs and scanning inputs. The transfer of information is completely transparent - the systems engineer does not have to understand the communications protocols at all.
Communication with the device interfaces is by fiber optics, providing not only superior noise immunity and high voltage isolation, but fast data transfer as well.
Group3 Control's modular architecture produces a cost-effective, high-performance control system that is easily configured to a particular application.
A wide variety of I/O boards is available, allowing a great deal of flexibility in setting up the distribution of control points in a system. A DI can be populated with just the type of I/O required at that point. The I/O boards available are:
| Type | Features |
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| B |
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| C |
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| D |
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| E |
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| F |
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| G |
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| H |
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| J |
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The CNA, a combined processor, I/O and signal conditioning module, offering:
- 2 analog inputs
- 1 analog output
- 8 optocoupled digital inputs
- 8 relay contact digital outputs
The CNA is a multi-function module combining communications processor, analog & digital I/O and signal conditioning in one compact machine.The unit is housed in a small aluminium case, and has built in PID closed loop control capability.
The small size of device interfaces means that they can be located close to the monitored and controlled points, reducing the length of wiring harnesses. This presents a significant cost saving, but also leads to a reduction in electromagnetic interference (EMI) received by signal lines in electrically noisy environments.
Each device interface module has an auxiliary port to be used for diagnostic and system configuration purposes. Connecting a terminal to this port allows the user to control and monitor all outputs and inputs on the device interface.
An installation can easily be expanded to cater for the growing needs of a user. Up to 16 device interfaces, each with 3 I/O boards, can be connected on a single fiber optic loop. More loops can be added for expansion.
To complete the control system Group3 recommends, and can supply, a number of commercially available software packages to provide a user interface at the computer. These packages provide for:
- data acquisition
- control
- automation
- data logging etc
Group3 Control - Key Features
- Fiber Optics - high voltage isolation - noise immunity.
- Small Size - easy mounting - keep wiring short to minimise noise pickup.
- Modular Design - Flexibility in configuring systems of any size.
- High Resolution - 16 bit analogs
- High Update Rate - scan rates of up to 32,000 channels per second
- High channel Density - several thousand channels per computer slot
- Diagnostic Port - on device interfaces for system development and debugging.
- Rugged Reliable Operation - fault tolerant and self correcting software in the modules
- Choice of software packages for operator interface.
- Cost Effective - high performance system at a budget price