This article explains the correct method of wiring Q.bloxx Classic modules in a distributed system setup in an industrial environment.
Introduction
The Q.station 101 controller has four universal asynchronous receiver-transmitter (UART) interfaces for communication over an RS-485 bus with the Q.bloxx 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 101 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.
Daisy-chained Distributed System Layout
How to connect Q.bloxx modules to a Q.station 101
The schematic below shows the RS-485 and power connection between the Q.station 101 and the first Q.bloxx module on that UART using an 8-pole pluggable terminal block (orange).
One 8-pole pluggable terminal block is included with each Q.station 101. Additional terminals must be ordered separately (Terminal block 8pol orange left for UART Q.series, article number 757789).
Please refer to the Q.station 101 or the Q.bloxx manual for more details about wiring a Q.bloxx Classic system.
Wiring requirements for a distributed measurement setup
To daisy-chain modules on one UART, an additional 8-pole pluggable terminal block (black) is required on the right-hand side of the module, where the cable to the next module will be connected.
These additional terminals must be ordered separately (Terminal block 8pol black right for UART Q.series, article number 930580).
Additionally, an extension socket (Q.bloxx base extension, article number 792081)may be required to connect an additional 10-30 VDC power supply if the voltage drop over the cable is too high to power all modules on one chain.
Please refer to Chapter 4 of the Q.bloxx manual for more details on calculating voltage drop and using the extension socket. Alternatively, contact your local Gantner Instruments representative for support.
How to connect e.bloxx modules to a Q.station 101
Q.bloxx modules must be addressed before e.bloxx modules on a UART. Skip an address in the sequence before addressing an e.bloxx module.
How to connect Q.bloxx modules to a Q.station X
To connect a Q.bloxx Classic module to a Q.station X, a so-called extension socket must be used. The extension socket is an adapter that converts the PCB backplane connector on the Q.station X to a screw terminal connector for easy wiring. The extension socket includes connections for both the RS-485 bus communication and the power supply for the Q.bloxx modules:
Please also refer to this knowledge base article for more details about the extension socket pin assignment and wiring.
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.
| 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 |
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.