Siemens AS-i SlimLine Diagnostic Guidelines

Engineering selection and fault diagnosis of Siemens AS-i SlimLine Compact module

In industrial fieldbus applications, AS Interface (AS-i) is widely used to connect sensors and actuators due to its advantages of simple wiring and low cost. However, as the control cabinet space becomes increasingly tight, higher requirements have been put forward for the width and functional integration of I/O modules. The Siemens SlimLine Compact series (3RK1/3RK2) is designed for this purpose: its digital, ASIsafe, and analog module widths are only 17.5mm or 22.5mm, and it achieves fast loops for AS-i and auxiliary power Uaux through optional device connectors. This article provides a detailed overview of the mechanical installation, electrical wiring, addressing configuration, core parameters of various types of SlimLine Compact modules, as well as LED based fault diagnosis methods from an engineering practical perspective, to help on-site engineers quickly locate problems during debugging and maintenance.

Product series and selection points

SlimLine Compact modules are divided into three categories based on their functions: digital I/O modules, ASIsafe modules, and analog modules. Its most prominent advantages are width reduction and flexible switching of sensor power supply.

1.1 Digital quantity module

The digital module covers multiple types of slave stations:

Pure input module: 4DI, supports 2-wire or 3-wire sensors. The 2-wire sensor version (such as 3RK2200-0Cx00) has a width of only 17.5mm and is powered by AS-i; The 3-wire sensor version (3RK2200-2Cx00) has a width of 22.5mm and can be powered by AS-i or Uaux through the back dial switch.

Input+output module: 4DI/4DQ (transistor output) or 4DI/4RQ (relay output), with a width of 22.5mm. The output current capability is 2A (PNP), and the relay contacts can be either normally open or conversion type.

Pure output module: 4DQ transistor output (such as 3RK2100-1Cx00), width 22.5mm.

Attention should be paid when selecting: if a 2A or above drive or AC load is required, a relay output type must be selected; For high-speed switch applications (PWM or frequent action), transistor output is more suitable.

1.2 ASIsafe module

The safety module is used to connect mechanical contacts such as emergency stop buttons and safety door switches, and complies with ISO 13849-1. Provide two models:

2F-DI (such as 3RK1205-0Bx00): Two fail safe inputs with a width of only 17.5mm. Designed specifically for mechanical contacts and not suitable for semiconductor output sensors.

2F-DI/2DQ (such as 3RK1405-2Bx00): Two fail safe inputs+two standard PNP outputs, with a width of 17.5mm. The standard output can be powered by AS-i or Uaux and selected through a dip switch.

The safety module does not occupy additional safety relays and communicates directly with the safety master station through the AS-i Safety protocol, achieving SIL2/PL level d.

1.3 Analog module

The analog module is divided into three categories, with an average width of 22.5mm:

4AI voltage/current switchable (3RK1207-0Cx00): Four analog inputs can be selected through DIP switches for ± 10V, 0-20mA, and 4-20mA, respectively. Priority should be given to using Uaux for sensor power supply (if connected), otherwise it will automatically be taken from AS-i (total current ≤ 46mA, otherwise Uaux needs to be connected).

4AI Pt100/Ni100/resistor (3RK1207-3Cx00): Used for measuring thermal resistors (Pt100, Ni100) or 0-600 Ω resistors, supporting 2/3/4 wire connections.

2AO voltage/current switchable (3RK1107-0Bx00): Two analog outputs that can be switched to ± 10V, 0~10V, 1~5V, 0~20mA, 4~20mA, or ± 20mA. The output has short-circuit protection and no-load protection.

The parameters of the analog module (filtering frequency, smoothing filter, range) are configured through the AS-i master station parameter bits (P3-P0), and the specific correspondence is described in Chapter 9 of the manual.

Mechanical installation and use of equipment connectors

SlimLine Compact supports two installation methods: standard 35mm DIN rail and wall mounting. Among them, device connectors can greatly simplify the wiring of AS-i and Uaux.

2.1 Rail Installation (Direct Installation)

Insert the upper part of the module back into the upper edge of the guide rail, and then press the lower half until you hear a "click" sound. When disassembling, first unplug the terminal, press the module down with a screwdriver, pull out the lower half, and then lift it up.

2.2 Equipment connector installation (recommended for parallel connection of multiple modules)

There are two types of device connectors: regular connectors (3RK1901-1YA00 is 17.5mm wide, 3RK1901-1YA10 is 22.5mm wide) and terminal connectors (with left cover, 3RK1901-1YA01/1YA11). The usage steps are as follows:

Insert the connector onto the guide rail and push it side by side until it clicks into place.

Install a terminal connector (with cover plate) at the far left end of the link.

Insert each module directly into the corresponding connector, and AS-i and Uaux will be automatically connected in series to each module through the internal busbar of the connector, without the need for additional wiring.

This design allows the entire cabinet to be connected to only the AS-i cable and 24V auxiliary power supply at the first connector, and subsequent modules will automatically receive power and communication, greatly saving wiring time.

2.3 Wall Installation

For chassis without rails, push in fixing ears (3ZY1311-0AA00) can be used to secure the module. Insert the fixed ear into the reserved slot on the side of the module, and then tighten it with an M4 × 12 screw through the long hole of the fixed ear (torque<0.1Nm for the upper part and 1Nm for the lower part). If installing the device connector on the wall, the connector needs to be fixed to the wall with screws first, and then the module needs to be fastened.

2.4 Terminal Types and Wiring Rules

The module provides two types of detachable terminals: screw terminals (recommended torque 0.6~0.8Nm, PZ1 screwdriver) and push in spring terminals. For spring terminals, hard wires or wires with cold pressed ends can be directly inserted into circular holes; Thin multi strand wire needs to be pressed into the rectangular hole with a 3mm flat screwdriver to open the spring, and then inserted into the wire. The recommended cross-sectional area of the wire is 0.5-1.5mm ² (AWG 20-16). The terminal positions are numbered, and the corresponding terminal function identification is printed on the inner side of the upper and lower cover plates to prevent incorrect wiring during module replacement.

Addressing and System Integration

Each AS-i slave must have a unique address (1-31 or 1A~31B). The SlimLine Compact module is connected to addressing devices (such as AS-i Handheld) through the "ADDR" circular hole on the front panel.

Non A/B slave stations (some models starting with 3RK1) occupy a standard address, ranging from 1 to 31.

A/B slaves (starting with 3RK2) support extended address mode, and the same physical address can accommodate two slaves, A and B, with a maximum of 62 slaves. The manual recommends using only address A or B for faster transmission.

When addressing, insert the connection line of the addressing device into the ADDR socket, and the module will temporarily disconnect from the AS-i bus. After writing the address according to the operating instructions of the addressing device, simply unplug it. The new module has a factory address of "0" and must be assigned a valid address to be recognized by the main station.

In depth Digital Module: Sensor Power Supply and Output Characteristics

4.1 Sensor Power Supply Selection

For digital modules that support AS-i/AUX switching, there is a dip switch on the back: when in position "AS-i", the sensor power is taken from AS-i voltage (about 30V DC), providing a maximum total current of 200mA (40 ° C environment); When in position "Uaux", it is taken from a 24V auxiliary power supply and provides a maximum total current of 500mA. This design allows high-power sensors (such as photoelectric switches) to be powered by Uaux, avoiding AS-i voltage drops.

No matter which power supply is chosen, the sensor wiring method remains unchanged: connected to the I+and I - terminals. If the sensor is a 2-wire system, it should be connected in series between I+and I -; In the 3-wire system, I+represents positive power supply, I - represents negative power supply, and the signal line is connected to INx.

4.2 Input electrical specifications

The digital input complies with the PNP Type 2 standard (EN 61131-2). High level threshold ≥ 10V, input current ≥ 6mA; low level ≤ 1.5mA. Therefore, NPN sensors cannot be directly connected and external relays or converters are required.

4.3 Output protection and fault indication

The transistor output (DQx) has overload detection function. When a channel is overloaded, the LED of that channel turns red, and the AS-i master station can read the I/O fault bit (only supported by A/B slave stations). The relay output (RQx) does not have overload detection, but can be protected by external fuses.

When communication is interrupted (such as when the main station is offline), the output will reset after 40-100ms (cycle time monitoring). The standard output of the ASIsafe module is also reset when safety communication is interrupted.

Special requirements for ASIsafe module

The safety input F-INx must be connected to mechanical contacts and cannot be connected to semiconductor output sensors. Each safety input has two wires: F-INx and GND. The module will undergo pulse testing and short circuit detection internally to achieve a safe circuit.

For 3RK1405-2Bx00, the standard outputs (DQ0, DQ1) can be selected from AS-i or Uaux power sources through another back dip switch. If AS-i is used for power supply, output overload will cause the entire module to shut down communication (FAULT LED red); If Uaux is used for power supply, overload only causes the corresponding output LED to turn red, without affecting communication.

The safety module does not transmit I/O fault bits, and diagnosis relies entirely on LED indications.

Analog module configuration and accuracy

6.1 Input module wiring differences

Current measurement: For 2-wire sensors, the sensor power supply needs to be connected between Lx+and Mx, and AIx+and AIx - short circuited; The 4-wire system is connected to AIx+and AIx - respectively.

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).

8.3 Problem: Large fluctuations in analog input readings

Reason: Shielded twisted pair cables were not used, common mode voltage exceeded ± 2V, or jumper wires were not added between AIx - and Mx. Solution: Check the wiring and add jumper wires for voltage input; Set the filtering to 50/60Hz and turn on smoothing (P2=0) in a strong interference environment.

8.4 Problem: Only some of the modules on the device connector are working

Reason: Poor contact of AS-i or Uaux inside the connector. Solution: Pull the module out of the connector, check if the metal spring of the connector is deformed, and re insert it. Pay attention to the maximum loop current - the total current of all modules' sensors cannot exceed the Uaux power supply capacity of the first inlet.

Maintenance and spare parts recommendations

Terminal coding: Using the 3ZY1440-1AA00 coding pin can prevent the accidental insertion of terminals with different functions. When replacing a module, insert the coding pin into the corresponding hole of the terminal block of the new module in its original position.

Memory card/label: 3RT2900-1SBxx device identification label can be used to mark the address and signal name of each module.

Technical data query: Enter the complete order number (such as 3RK2402-2CE00-2AA2) in Siemens Industrial Online Support (support. industry. siemens. com) to obtain the latest data sheets, certifications, and dimension drawings.

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