Wiring and installation recommendations for the model TBX AMS 620
(Original Document)
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Wiring recommendations
To protect the signal from induced external noise in serial mode and noise in common mode, it is advisable to take the following precautions regarding:
Precautions to take
Type of conductors
Use screened twisted pairs, with a minimum conductor cross-section of 0.28 mm2.
Cable screening
Connect the cable screening to the shortest TBX module ground on the TBX GND 015 grounding strip.
Arrangement of the conductors in cables
Multipair cables can be rearranged for signals of a similar type which have the same reference to ground.
Cable routing
Keep the measurement wires separate from the discrete I/O cables (in particular from relay outputs) and from power cables.
Preactuator and sensor reference to ground
The TBX AMS 620 module has 6 inputs which are not isolated from each other but which are isolated from the PLC bus, and 2 outputs which are isolated from each other and from the PLC bus.
The sensor cold points are connected to each other internally by the Com terminals.
To ensure good immunity to high frequency interference, a 4.7 nF capacitor is connected between the channel voltage and the ground.
To ensure correct operation of the analog measurement system, the following precautions must be taken:
  • The sensors must be in close proximity to each other (several meters apart).
  • All sensors must be referenced at the same point. This point is then connected to the terminal ground.
Note: There are no technical restrictions in referencing the preactuators to ground. However, for safety reasons, it is advisable to avoid using a ground voltage which is some distance from the terminal, as this ground voltage may be very different from the nearby ground voltage. Distributed I/O modules minimize this risk as they are usually close to the process.
Sensor reference to ground
If the following characteristics are respected, then each sensor can be assigned a voltage rate according to ground:
  • The sensors must be in close proximity to each other (several meters apart).
  • all sensors are referenced to the same point. This point is then connected to the COM terminal on the terminal block.
Preactuator reference to ground
  • Recommended voltage and current wiring:
    It is advisable to use preactuators which are not referenced with respect to ground, with each channel reference being connected to the ground via a 4.7 nF capacitor.
Preactuator reference to ground (cont.)
  • Possible voltage wiring:
    The preactuators can be referenced to ground if the modules have voltage outputs and if the following precautions are taken:
    • The common mode voltages must be below the safety voltage (48 V peak),
    • Connecting a point in the preactuator to a reference voltage causes a leakage current to be generated. If several analog modules are used, measure the total leakage current and check that it will not interfere with the application.