This article explains the correct method of wiring Q.bloxx XL modules in a distributed system setup in an industrial environment.
Introduction
The Q.station X controller has four universal asynchronous receiver-transmitter (UART) interfaces for communication over an RS-485 bus with the Q.bloxx XL modules. The RS-485 bus can either be connected via a backplane (integrated into the module's socket) or with wires in case the modules need to be installed remotely. Regardless of using a backplane or wired RS-485 bus connection, all measurement modules are automatically time-synchronized with a jitter of less than 2 µs.
The maximum number of modules that can be connected to one UART is 16, so a total of 64 modules to one Q.station X controller. However, the number of modules, or moreover the amount of data to be transmitted over the bus depends on the baud rate settings, which again depends on the total length of the RS-485 bus. See also section Baud rate versus bus length further down this page. 
RS-485 bus wiring with extension sockets
To connect the controller and measurement modules via a wired bus, so-called extension sockets must be used. The extension socket is an adapter that converts the PCB backplane connector to a screw terminal connector for easy wiring. The extension sockets include connections for both the RS-485 bus communication as well as the power supply for the measurement modules. There are two versions of the extension on the socket; the RIGHT version connects to the right-hand side of a module (to convert the backplane connector to screw terminals) and the LEFT version connects to the left-hand side of a module (to convert the screw terminals back to the backplane connector).
Q.bloxx XL extension sockets:
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Q.bloxx-X base left for UART and Supply, Article No. 544021 (datasheet)
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Q.bloxx-X UART/Power left, Article No. 561323 (datasheet)
Q.brixx XL extension sockets:
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Q.brixx-X UART/Power right, Article No. 611622
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Q.brixx-X UART/Power left, Article No. 646327
Extension socket pin assignment and wiring
Pin 1 and 2 on connector X10 (UART 1) must be wired. Wiring the other UARTs is optional, depending on the system configuration.
A 10 - 30 VDC power supply must be connected to pins 6 and 7 on connector X11 of the extension socket LEFT. This can either be the power supply coming from the controller (via the extension socket RIGHT) or a separate power supply.
The pin assignment is identical for both LEFT and RIGHT extension sockets.
| Connector X10 | |||
| 1 | RS485 1 A | UART 1, signal A | Mandatory |
| 2 | RS485 1 B | UART 1, signal B | Mandatory |
| 3 | RS485 2 A | UART 2, signal A | Optional |
| 4 | RS485 2 B | UART 2, signal B | Optional |
| 5 | RS485 3 A | UART 3, signal A | Optional |
| 6 | RS485 3 B | UART 3, signal B | Optional |
| 7 | RS485 4 A | UART 4, signal A | Optional |
| 8 | RS485 4 B | UART 4, signal B | Optional |
| Connector X11 | |||
| 1 | RS485 ACYCL A | Acyclic data exchange | Not used |
| 2 | RS485 ACYCL B | Acyclic data exchange | Not used |
| 3 | DIG slot | - | Not used |
| 4 | VS+ | Add. sensor excitation supply | Optional |
| 5 | VS- | Add. sensor excitation ground | Optional |
| 6 | VIN | Module power supply 10 - 30 VDC | Mandatory |
| 7 | GND | Module power supply ground | Mandatory |
| 8 | CGND | Chassis ground | Optional |
Baud rate versus bus length
Depending on the bus length, you may have to reduce the speed of data transmission (baud rate). The factory default setting is 24 Mbps. See the below table for recommended baud rate settings.
The baud rate setting of the controller can be configured in GI.bench (Controller → RS485 adapter → General → Baudrate). GI.bench automatically checks if the configured number of modules, variables, and sample rate fit within the configured baud rate. In case of an error, either reduce the number of modules/variables on a UART or select a slower sample rate.
The overall bus length of a serial interface cable consists of the length of all cables between the individual modules and the cable length to the centralized controller. Whatever the cable length and baud rate, the number of modules per UART remains at 16. With baud rates from 1.5 Mbps or lower, it is recommended to install at least 1 meter of cable between 2 adjacent devices. A baud rate of 48 Mpbs can only be used with a backplane bus, not with a wired bus.
| Baud rate | Maximum bus length |
|---|---|
| 187.5 kbps | 1000 m |
| 500 kbps | 400 m |
| 1.5 Mbps | 200 m |
| 3 Mbps | 100 m |
| 6 Mbps | 20 m |
| 12 Mbps | 10 m |
| 24 Mbps | 10 m |
| 48 Mbps | backplane only |
Cable requirements
The recommended baud rate setting only applies when using a PROFIBUS cable within the IEC 61158 standard. If an alternative cable is used, the above table will not apply and the long-term consequences concerning reliability are not guaranteed.
To minimize the risk of electrical interference on the bus, it is recommended to use a cable that is manufactured according to IEC 61158 (also known as Type 3 or PROFIBUS cable). The IEC 61158 cable for PROFIBUS is a 2-wire (shielded twisted pair) cable, generally with an Aluminum Polyester Tape shielding and a tinned copper wire braid (TCWB) or steel wire armor (SWA) to offer protection from crosstalk and electromagnetic interference.
There are exceptions to the PROFIBUS installation guidelines; cables that need to meet special environmental conditions may not always reach the specified bus length and provide reliable communication. This information should be stated in the datasheets of the cable manufacturers.