How to Wire Q.bloxx XL Modules in a Distributed System

To wire distributed Q.bloxx XL modules, use compatible extension adapters to connect communication and power between module groups. Identify the adapter type before following a pin assignment: extension sockets and UART/Power modules have different connector layouts. Check the applicable datasheet before making connections.

Distributed system architecture

The Q.station X controller provides four UART interfaces for RS-485 communication with Q.bloxx XL modules. Modules can be connected either through the integrated backplane in the module sockets or via RS-485 cables for remote installations. In both configurations, all connected measurement modules are automatically time-synchronised with a maximum jitter of ±0.5 µs, without requiring manual configuration.

Each UART supports up to 16 modules, allowing a maximum of 64 modules per Q.station X controller. However, the achievable data throughput and number of connected modules depend on the configured baud rate, which is limited by the total RS-485 bus length.

For more information, see Baud rate versus bus length.

Extension adapters for distributed wiring

To connect the Q.station X controller and measurement modules via a wired RS-485 bus, extension sockets are required. These adapters convert the integrated PCB backplane connectors into screw terminals, allowing easy connection of the RS-485 communication bus and power supply to the measurement modules.

Two versions of the extension socket are available for connecting Q.bloxx XL modules via a wired RS-485 bus:

LEFT extension socket: Connects to the left-hand side of the module, converting screw terminal connections into the integrated backplane connection.
RIGHT extension socket: Connects to the right-hand side of the module, converting the integrated backplane connection into screw terminal connections.

Q.bloxx XL extension sockets:

Q.bloxx-X base left for UART and Supply, Article No. 544021 (datasheet)
Q.bloxx-X base right for UART and Supply, Article No. 544122 (datasheet)

Q.bloxx XL extension module:

Q.bloxx-X UART/Power left,
Article No. 561323 (datasheet)
Q.bloxx-X UART/Power right,
Article No. 561424 (datasheet)

Extension socket connections and power supply

Pins 1 and 2 of connector X10 (UART 1) must be connected for RS-485 communication. Connections to the other UART interfaces are optional, depending on the system configuration.

A 10–30 VDC power supply must be connected to pins 6 and 7 of connector X11 on the LEFT extension socket. Power can be supplied either from the Q.station X controller via the RIGHT extension socket or from a separate external power supply.

The pin assignments are identical for both the 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

Select the baud rate for the total bus length

Depending on the RS-485 bus length, the communication speed (baud rate) may need to be reduced to ensure reliable data transmission. The factory default is 24 Mbps. Refer to the table below for the recommended baud rates at different bus lengths.

The baud rate is configured in GI.bench > Controller > RS485 adapter > General > Baudrate. GI.bench automatically checks whether the configured modules, variables and sampling rates can be supported by the selected baud rate. If the configuration exceeds the available bus capacity, reduce the number of modules or variables on the UART, or lower the sampling rate.

The total bus length includes all cables between connected modules, as well as the cable connecting the modules to the central controller. Each UART supports a maximum of 16 modules, regardless of the bus length or baud rate.

For baud rates of 1.5 Mbps or lower, maintain a minimum cable length of 1 metre between adjacent devices.

The maximum baud rate of 48 Mbps is supported only when modules are connected via the integrated backplane. It cannot be used with a wired RS-485 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

Configure bus termination

Q.series X modules feature an integrated 50 Ω termination resistor, optimised for short bus connections and high communication speeds of up to 48 Mbps. However, this termination resistance may not be optimal for longer RS-485 bus cables.

For longer cable runs, an external termination resistor between 50 Ω and 120 Ω may provide better signal integrity. The optimal resistance depends on the number of connected modules, cable type, cable length and communication speed. Some practical testing may therefore be required to determine the most reliable configuration.

Important: When using an external termination resistor, disable the internal termination by setting DIP switches 9 and 10 to OFF. Connect the external termination resistor directly between the RS-485 A and B signal lines at the appropriate bus termination point.

Select a suitable bus cable

The recommended baud rates and maximum bus lengths apply only when using PROFIBUS cables compliant with IEC 61158. Other cable types may have different electrical characteristics, potentially reducing the achievable bus length and affecting long-term communication reliability.

To minimise electrical interference, use shielded twisted-pair cables designed for PROFIBUS applications (IEC 61158, Type 3). These typically consist of a two-wire twisted pair with aluminium-polyester tape shielding, often combined with a tinned copper wire braid (TCWB) or steel wire armour (SWA) for additional protection against electromagnetic interference.

Note: Cables designed for special environmental conditions may have different electrical characteristics and may not support the specified baud rates or maximum bus lengths. Always consult the cable manufacturer's datasheet to verify suitability for the intended installation.

Gantner Instruments recommends LAPP UNITRONIC BUS PB cables for reliable RS-485 communication.

Frequently asked questions about Q.bloxx XL distributed wiring

Do all extension adapters have the same pin assignment?

No. The linked extension socket and UART/Power module datasheets show different connector layouts. Use the datasheet matching the installed adapter.

Can extension sockets carry communication and module power?

Yes. The extension socket documentation provides connections for both communication and power between distributed module groups.

What supply voltage does the extension socket require?

The extension socket specifies a module supply of 10–30 volts direct current, connected to X11 terminal 6 and terminal 7 for supply and ground respectively.