Twisted Pair Medium

Overview | Cable Shielding | Controller Shielding | Node Shielding

Overview

This is described in the following documents. SynqNet follows these two documents in every respect.

SynqNet has defined two standard connectors: RJ-45 and Micro-D. The RJ-45 connector is standard for commercial 100BT applications and conforms to CAT-5. MEI currently uses the RJ-45 connector in a horizontal orientation. If you wish to use a vertical RJ-45, please contact MEI.

As an alternative to the RJ-45, where additional tolerance of vibration is required, the commercial Micro-D connector (Molex Part No. 83611-9006) is supported. MEI currently uses the Micro-D connector in a horizontal orientation. If you wish to use a vertical Micro-D, please contact MEI.

The cabling scheme uses straight through cables. The crossover of transmit and receive is carried out at the connectors. These two pinouts have been named the "OUT" port and the "IN" port to assist in the setup of hardware , but remember that each port is full duplex and has the ability to transmit and receive data. Please see the following links for pinout information: Micro-D or RJ-45.

Cable Shielding

SynqNet defines cable shielding conventions in order to properly isolate local node signals and power while minimizing EMI (both emission and reception). Shielded cabling is strongly recommended for SynqNet. This will reduce EMI coupled from other devices in the system. The cables shall have their shields connected to the metal connector shell using the crimped collar (on RJ-45s) or clamp (on Micro-D). The use of unshielded cabling is permitted but not preferred. Cable shield connections are treated slightly differently at the controller and node PCBs. Both are detailed below.

Controller Shielding

Controller shielding follows standard 100BT NIC design conventions: the connector shell shall tie to the bracket or front panel, and not directly connected to the controller's local digital ground (the host computer chassis is responsible for grounding the chassis, which is normally tied to a safety ground at a central point along with digital ground). The cable shield shall also tie to an isolated plane section on the controller PCB to minimize EMI.

Node Shielding

Node shielding shall be DC isolated from port to port and from local node chassis, as well as from ground and power signals. (Molex offers an insulated screened connector that makes this a lot easier to implement: PN 85504.) This prevents currents at DC or main frequency from circling the ring, or coming back via some system ground path. The shields are AC coupled via capacitors (one for each port) to a nearby earth point on the node and/or machine chassis. The capacitor value shall be between 1 nF and 10 nF, and the rated voltage shall be 2000 V. This capacitor reduces EMI by dumping high frequency energy to the earth ground. The cable shields are also tied to isolated plane sections (one for each port) on the node PCB to minimize EMI.

In conformance with normal industrial practice it is recommended that the local logic power supplies within a node should be derived using a local isolating power supply and that the 0V should be grounded locally.