Products Affected: All system using QLink hardware

QLink uses a high-speed, RS-485 communications protocol for sending and receiving data to the greenhouse.  You will find this system to be extremely reliable and durable, if installed properly.  In addition, the way you install your cable can have a definite effect on the system’s final communications performance.  This being the case, it is helpful to know a few things about the do’s and don’ts of installing this cabling.

Plan Your Cable Layout
To make your cable installation as easy as possible, you need to know the characteristics of this communications system.  Here are some pointers and tips to keep in mind when planning your cable runs:

NOTE: You will have four PORTS available on your QLink system.  This can be a handy option, allowing you to run separate cables in up to four different directions from the computer to the QLink boxes in the greenhouse.

• The boxes MUST be wired in what is known as a BUS topology, or more commonly known as a daisy-chain.  This means that the cable runs to the first box, then out of the first box to the second box, and so on (see Figure-1).  Cables run in this daisy-chain fashion can be up to 4,000 feet long and handle up to 100 QLink boxes.  We will refer to this main, daisy-chained cable as the BACKBONE in this document.  Remember that you can have up to four backbone cables in this system, one from each port of the DL-400 data-link.  NOTE: BACKBONE cables must have a 120-ohm terminating resistor installed on the last box on the backbone.

There is one exception to this daisy-chained rule:

• Cable runs that are less than 100 feet long (total length, including what’s inside the QLink boxes) can be run off the backbone cable in a STAR configuration.  An example might be a panel that the backbone cable passes on its way to other QLink equipment.  Instead of running the backbone cable into the panel, daisy-chaining each box, and then running out again, you can run a short cable off the backbone into the panel.  This STAR cable, as we will refer to it from this point, can then be daisy-chained to each box.  NOTE: Boxes installed on star cables are added to the number of boxes on the backbone to total no more than 100 boxes.  STAR cables should NOT have a terminating resistor installed on the last box in the daisy-chain.

Helpful Hint: If you are making daisy-chain connections there will only be two cables attached to each motherboard, the one entering the box and the one leaving to go to the next box.  However, if there are three cables attached to a motherboard, that is a star connection.

• The cable you use must be shielded, and the shield drain wires MUST be terminated as shown on the QLink wiring diagrams (J8 Lug-3).  This keeps the shield drain wire electrically continuous back to the TVSS (transient voltage surge suppressor; sometimes called a lightning arrestor) for proper grounding.  This helps to eliminate outside interference on the network.

Install the Cable
After you have determined the general layout of the cable run(s), you can install the cable itself.  If you are using the standard cable supplied by QCOM, with the heavy PVC jacket, no conduit or raceway is required.  However, you should make certain that the cable is protected from damage and is properly supported.  If you are using tie-wraps to attach the cable to greenhouse structures, be sure to use the UV-resistant type.

Run the cable into each QLink box, and then out again to the next box.  Make sure to leave plenty of cable in each box to reach the connector in the upper left-hand quadrant of the motherboard labeled J8.  Install the wires as shown in the QLink wiring diagrams.  Remember to terminate the backbone run of cable with a 120-ohm resistor.  NOTE: each QLink motherboard comes with a 120-ohm resistor installed across the J8 connector (where the communication cable connects).  This resistor must be REMOVED from all boards but the last one on the backbone run.  Star cable runs (must be less than 100 feet long) are never terminated with a resistor.

Please contact us if you have any questions about installing your QLink communications cable.

Figure 1 - Sample Cable Routing*

Ú This sample is for illustration only.  Your layout will probably differ considerably from this simple example.