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I am working on a project to upgrade several (100s) of existing 4-20mA system. All these systems are at different locations but use a similar topology:
- Star topology
- Up to 28 nodes (most have 16 or less)
- Each node is connected via 24AWG unshielded twisted pairs (just two wires)
- Wiring length to each node is a maximum of 120ft away from central connection hub
The project requirement forces us to use the existing wiring. We cannot pull new wires to the new devices. We cannot use a wireless interface.
Standard mains power (120 volt) is available at each node. There are only two conductors available for communication. There is no shield or ground wire -- just the two twisted wires connected to a central hub 120ft or less away.
The new devices provide bi-directional measurement and control. Each node will transmit and receive up to 4kb (4 kilobytes) of data at a time. We'd rather not have a master-slave system but allow each node to send data when it's available (asynchronous). Obviously that means there would be collision issues. Fast speed and multi-drop would be ideal [Ethernet on two conductors ?!?].
The new nodes are comprised of sensors, actuators, a single board computer and whatever communication interface we select.
We are looking at HART but afraid of the low speed and polling issues for fast response.
Remembering that there are only two wires (existing 4-20mA analog wiring) used for communication what other existing network system could you recommend?
Thank you.
- Star topology
- Up to 28 nodes (most have 16 or less)
- Each node is connected via 24AWG unshielded twisted pairs (just two wires)
- Wiring length to each node is a maximum of 120ft away from central connection hub
The project requirement forces us to use the existing wiring. We cannot pull new wires to the new devices. We cannot use a wireless interface.
Standard mains power (120 volt) is available at each node. There are only two conductors available for communication. There is no shield or ground wire -- just the two twisted wires connected to a central hub 120ft or less away.
The new devices provide bi-directional measurement and control. Each node will transmit and receive up to 4kb (4 kilobytes) of data at a time. We'd rather not have a master-slave system but allow each node to send data when it's available (asynchronous). Obviously that means there would be collision issues. Fast speed and multi-drop would be ideal [Ethernet on two conductors ?!?].
The new nodes are comprised of sensors, actuators, a single board computer and whatever communication interface we select.
We are looking at HART but afraid of the low speed and polling issues for fast response.
Remembering that there are only two wires (existing 4-20mA analog wiring) used for communication what other existing network system could you recommend?
Thank you.