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 features four universal asynchronous receiver-transmitter (UART) interfaces for communication with Q.bloxx modules over an RS-485 bus. The RS-485 connection can be established either via a backplane (integrated into the module socket) or using wired connections when remote installation is required. In both cases, all connected measurement modules are automatically time-synchronized with a jitter of ±0.5 µs.
Each UART supports up to 16 modules, allowing a maximum of 64 modules per Q.station 101. However, the number of modules—and more importantly, the volume of data that can be transmitted—depends on the configured baud rate, which is in turn influenced by the total length of the RS-485 bus. See section "Baud rate versus bus length" for more details.
How to connect Q.bloxx modules to a Q.station 101
The schematic below illustrates the RS-485 and power connections between the Q.station 101 and the first Q.bloxx module on that UART, using an 8-way pluggable terminal block (orange).
Each Q.station 101 is supplied with one 8-way pluggable terminal block. Additional terminal blocks must be ordered separately.
- Gantner Instruments Art. No. 757789 (Terminal block 8pol orange left for UART Q.series)
- Phoenix Contact MC 1,5/ 8-ST-3,81 OG
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 multiple modules on a single UART, an additional 8-way pluggable terminal block (black) is required on the right-hand side of each module. This is where the cable to the next module in the chain is connected.
These terminal blocks must be ordered separately:
- Gantner Instruments Art. No. 930580 (Terminal block 8pol black right for UART Q.series)
- Weidmüller SCZ 3.81/08/180G SN OR BX
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.