Other Uses
DI to DI communications mode
Group3 Device Interfaces connected with just two fiber optic cables provide noise free transmission of many analog and digital signals in difficult environments.
High voltage isolation and long distance transfer of signals are simple to implement using this low cost system.
The system uses the same well proven hardware of the computer based system, but in a new configuration in which two Device Interface (DI) modules communicate with each other, not with a computer.
If, for example, a signal voltage is presented to an analog input channel in one DI, the exact same voltage will be generated by a corresponding output channel in the other DI module. Digital on/off channels are similarly replicated by the system - if a switch is closed that grounds a digital input channel in one DI, the corresponding output in the other DI will be clamped to its ground level.
The transmission of data is over two fiber optic cables, providing noise immunity and voltage isolation for electrical signals present at each end of the cables.
Two fiber optic cables are easier to install and considerably less expensive than a bundle of shielded cables over long distances. If glass fiber optic cables are used the DIs can be up to 3000 metres apart. Plastic fiber optic cables can be used for distances up to 40 metres.
The DI modules and I/O cards are standard components of the Group3 Control range, so at a later date they could be used as part of a full computer based control system if required.
Boards available to use for this system are:
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Type A
Combined analog and digital board.
In this system provides 1 analog input, 1 analog output, and 8 digitals
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Type B
24 digital channels
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Type C
Eight analog inputs.(ADCs)
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Type D
Eight analog outputs.(DACs)
Some examples:
- If a type B board in one DI is matched to another B board in the other DI, it gives 24 channels of digital on/off signals. Each channel can be set to operate in either direction.
- Two DIs, each with 3 boards - a B, C, and a D, gives 24 digital signal lines, and 8 analog monitoring channels, and 8 analog control channels.
If the range settings of the analog channels are set appropriately then it is possible to have the system insert a gain factor during transmission. For example a 0-50mv input signal could be transformed to a 0-10 volt output just by setting the input and output ranges to those values.
topLC to LC communications mode
Group3 Loop Controllers can be used to provide a fiber optic data communications channel between computers. High voltage isolation and long distance transfer of data are simple to implement using this low cost system.
This use of the Group3 LC card allows two computers to share information, using fiber optic cables. Two LCs, one in each computer, continually exchange the data held in defined areas of their memories. If one computer writes some data into the transmit area of its memory, this data will automatically appear a few milliseconds later in the receive area of the other computer's memory. At the same time data can be transferred in the other direction as well.
The computers could be two of the same type (two PCs talking, or two VME crates talking to each other), or of different types (A PC talking to a VME crate, or a VME crate talking to an STD crate, for example). The LC to LC protocol thus provides an isolated communication channel between different computer platforms.
topLC to DTMs / General ASCII communications mode
Group3 Loop Controllers can be used to monitor and control a loop of Group3 Digital Teslameters (DTMs), or communicate with any other serially driven device.
Up to 32 Teslameters can be connected together on a fiber optic loop from each loop controller. The processor on the loop controller automatically and continuously interrogates and updates each teslameter, placing the readings it gathers in the dual port RAM. The host computer can then access these readings at any time under program control.
If in general ASCII mode, any message string the computer writes into a certain memory area will be transmitted out on the fiber optic cables, and any message received over the fiber optic cable will be written into a different memory area. The control computer can then read and act upon the message.
For RS-232 serially controlled instruments Group3 manufacture a small converter to change the fiber optic serial data to RS-232 data. This unit is called an FTR.
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