General precautions

General precautions

Introduction While installing the yellow AS-i cable, it is essential to place it in a cable track which is separate from the power cables. It is also advisable to place it flat and not twisted. This will help make the two AS-i cable wires as symmetrical as possible. Installing the AS-i cable on a surface connected to the electric potential of the machine (for example, the housing) complies with the requirements of the EMC (Electro Magnetic Compatibility) directive.

The end of the cable, or the ends in the case of a bus with a star-formation , must be protected either:

 by connecting it (them) to a T-derivation,  by not allowing them to come out of their last connection point.

Important It is important to distribute power effectively on the AS-i bus, so that each device on the bus is supplied with sufficient voltage to enable it to operate properly. To do this, certain rules must be followed.

Rule 1

Select the capacity of the supply module adapted to the total consumption of the AS-i segment. Available capacities are 2.4A (TSXSUPA02) and 5A (TSXSUPA05). A capacity of 2.4A is generally sufficient based on an average consumption of 65mA per slave for a segment made up of a maximum of 31 slaves.

Rule 2

To minimize the effect of voltage drops and reduce the cost of the cable, you must determine the best position of the supply module on the bus, as well as the minimum size of cable appropriate for distributing power. The voltage drop between the master and the last slave on the bus must not exceed 3V. For that purpose, the table below gives the essential points for selecting the cross-sectional measurement of the AS-i cable.

Table of characteristics:

Cross-section measurement of AS-i cable 0.75mm2 (28AWG) 1.5mm2 (14AWG) 2.5mm2 (12AWG)

Linear resistance 52milliOhms/meter 27milliOhms/meter16milliOhms/meter

Voltage drop for 1A over 100meters (328feet) 5.2V 2.7V 1.6V

The cable which can be used for most applications is the cable with a cross-section of 1.5mm2 (14AWG). This is the standard AS-i bus model (the cable is offered in the SCHNEIDER catalog). Smaller cables can be used when sensors consume very little power. NOTE: The maximum length of all the segments making up the AS-i bus without a relay is 100meters (328feet). The lengths of cables which link a slave to a passive distribution box must be taken into account.