Siemens AS-i SlimLine Diagnostic Guidelines

Voltage measurement: A 4-wire connection must be used, and jumper wires need to be added between AIx - and Mx to prevent the differential amplifier from being over driven due to 50Hz ripple from external sensor power supply.

Resistance/Thermistor: Four wire connection is optimal (eliminating line resistance). If using 2 or 3 wires, try to shorten the wire length as much as possible and connect jumper wires between AIx - and ICx -.

6.2 Channel Disabling and Transmission Time

The AI0 of the analog module is always activated, and AI1~AI3 can be disabled through DIP switches. After disabling, the AS-i loop no longer transmits data from these channels, thereby shortening the update time. For example, when two channels are activated, the conversion time for each channel is about 20ms (50Hz filtering), plus 7 × 2+7=21 AS-i cycles (maximum 5ms per cycle), the total transmission time is about 105ms. Smooth filtering (k=8) will further increase the stabilization time by about 8 × 130ms ≈ 1 second.

6.3 Parameterized Configuration

All analog parameters are issued through the parameter bits (P3-P0) of the AS-i master station. For example, for voltage/current input modules:

P3: 0=60Hz filtering, 1=50Hz filtering

P2: 0=Smooth on, 1=Smooth off

P1P0: Select range (01=± 20mA, 10=4~20mA 2-wire, 11=4~20mA 4-wire)

If the main station sends invalid parameters, the module defaults to using 4-20mA/4 wires or ± 10V (depending on the module). This design ensures a safe state during system startup.

6.4 Response time of output module

After receiving the new set value, the analog output module establishes a time of 0.6ms for resistive loads and 6ms for inductive/capacitive loads. The total maximum time from PLC transmission to actual output changes is ≤ PLC transmission time+105ms (AS-i transmission)+6ms ≈ 111ms. For fast analog control (such as proportional valves), this delay must be incorporated into the control circuit design.

LED diagnosis and troubleshooting

The front LED of the SlimLine Compact module provides rich operational status information, allowing engineers to diagnose the vast majority of faults without the need for software.

7.1 AS-i/AULT dual color LED (green/red)

Solution to the meaning of LED status

Green constant light AS-i communication is working normally

Red constantly on, no AS-i communication. Check if the master station is online, if the slave station address is correct, and if the slave station type matches

Red/green alternating flashing sensor power supply overload (digital module) or missing analog data exchange check if the total current of the sensor exceeds 200mA/500mA; For the simulation module, confirm that the main station supports analog exchange with Spec 2.1 or higher

Red/yellow flashing slave station address=0 (factory state) uses addressing devices to allocate addresses

Check if the AS-i power line is reversed or if the voltage is too low (should be ≈ 30V DC) when there is no AS-i voltage

Special note: For ASIsafe modules, if the standard output is powered by AS-i and overload occurs, the AS-i/AULT LED will flash green/red; If powered by Uaux, overload only causes the output LED to turn red.

7.2 AUX POWER Green LED

Green constantly on: Uaux (24V DC auxiliary voltage) is normal.

Extinguish: No Uaux or reversed polarity. Note: Some modules (such as pure digital inputs and sensors powered by AS-i) can work without Uaux, but analog inputs that require high current sensor power must be connected.

7.3 Input/Output LED

Digital Input (DIx) Yellow: Constant light indicates that the input is at a high level (signal activated).

Digital transistor output (DQx) dual color: yellow=output conduction; Red=This channel is overloaded (only valid when powered by Uaux); If powered by AS-i and overloaded, the module will shut down communication.

Relay output (RQx) yellow: Constant light indicates that the relay coil is energized (contact closed).

Safe input (F-INx) yellow: constantly on indicates that the safety circuit is closed (normal state).

7.4 Special Diagnosis of Analog Modules

The analog module does not have LEDs for each channel, and faults are mainly determined by AS-i/AULT LEDs and abnormal measurement values

When the analog input value is always 32767 (overflow) or -32768 (undercurrent/disconnection), check if the sensor wiring is open or if the range setting is correct.

The output module automatically outputs 0V/0mA after 5 seconds of no data exchange, and the FAILT LED is always red.

Common engineering problems and quick fixes

8.1 Problem: After module installation, the AS-i/AULT LED remains red and constantly on

Troubleshooting steps:

Confirm if the module has been assigned a non-zero address (read using addressing devices).

Confirm if the master station configuration includes the slave station type and I/O length (4I/4O for digital modules and 7.3. x profile for analog modules).

Check if the AS-i cable is reliably connected at the module, especially when using device connectors, to ensure that the connectors are securely fastened to each other.

8.2 Problem: Digital output does not work and LED turns red

Phenomenon: DQx LED is red. Reason: Output overload or short circuit. Solution: Disconnect the load to measure impedance, which should normally be high impedance; Check if the output is connected to an inductive load and there are no freewheeling diodes. After resolving the overload, the module automatically recovers (without burning the internal fuse).