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Entry type: FAQ Entry ID: 42806066, Entry date: 06/06/2016

AS-Interface: Compatibiliy for AS-i Power24V

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This FAQ content Statement which AS-i slaves can be employed with the new system extension AS-i Power24V.


Which AS-i slaves can be employed with the new system extension AS-i Power24V?



AS-i Power24V is an extension of the AS-i specification, in which the AS-i rated voltage, is reduced to 24 V.

AS-Interface is usually operated with rated voltage DC 30 V. An AS-i power supply (e.g. 3RX9501-2BA00) incorporates, besides the 30 V voltage supply, a so called data decoupling circuit which is required for the AS-i data transfer on the AS-i cable. Using an AS-i power supply, one can connect AS-i master and AS-i slaves without any additional components to the AS-i cable.

According to the extension of the AS-i specification it is alternatively feasible to use the rated voltage DC 24 V, and after that a standard 24 V power supply can be employed for alimentation of an AS-Interface system (AS-i Power24V). For the AS-i data transfer there is a data decoupling unit (e.g. 3RK1901-1DE12-1AA0) required, which is connected with the AS-i master and AS-i slaves.

The AS-i data quality is of an equally high grade in both operation modes. Up to 62 slaves (A/B) can be connected in each mode.

The 24 V power supply shall comply with the PELV standard (Protective Extra Low Voltage) and shall limit the residual ripple to max. 250 mVpp. SITOP power supplies are our recommendation.

As with all power supplies it shall be provided that the voltage on site of the load is sufficiently high.

In particular with a voltage of 24 V at the power supply one has to consider the line voltage drop on the AS-i cable. To restrict the line voltage drop, the AS-i cable length with AS-i Power24V is limited to 50 m, so that in practice sensors with a standard voltage range of 10...30 V can be supplied with sufficient voltage.

Slaves as well as sensors and actuators must be capable for the lower voltage.

No settings need to be made on the slaves with regard to AS-i Power24V.
All the Power24V slaves need to be supplied with at least 18 V AS-i voltage.

The attached table shows a listing which AS-i slaves are compatible for AS-i Power24V.

Calculation example:

The AS-i flat cable (2 x 1, 5 mm²) features a resistance of 0,025 Ohm/m (incl. go-and-return line), means that the line voltage drop counts 0, 25 V per each 10 m cable length and per 1 A current.

On 20 standard slaves each with 150 mA current drain (incl. approx. 100 mA consumption of the connected sensors), which are equally distributed along 50 m AS-i cable, the last sensor is energized with approx.18 V, if and when 24 V are fed in at the start of the AS-i cable run.

Approximate calculation:
24 V (power supply voltage) - 2 V (line voltage drop) - 4 V (slave voltage drop) = 18 V.

To increase the voltage impressed on the sensor, as far as possible the output voltage of the power supply can be adjusted to e.g. 26 V (depending on the properties of the power supply and the other connected loads).


  71129_AS-I_POWER24V_MASTER_SLAVES_2016-05-17.xls (73,0 KB) 


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