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The Pilz PSS SB DI8O8 is a programmable safety system module designed for use as a decentralized input/output device on SafetyBUS p, supporting a wide range of safety-related applications. This module provides 8 digital inputs, 8 digital outputs, and 2 dedicated test pulse outputs, making it versatile for connecting various safety-related input devices, whether single or dual-channel, and with or without test pulses.
The PSS SB DI8O8 operates by transmitting input status to the CPU on the PSS master via SafetyBUS p. Its diagnostic circuitry continuously checks the function of the inputs, including the input filter, and the status of the outputs. In the event of an error, all outputs in the affected I/O-group are switched off, and the I/O-group enters a STOP condition. An error telegram is then stored on SafetyBUS p, and the error is logged in the module's error buffer. This robust diagnostic capability ensures high safety integrity.
The module supports two 24 V supplies with a common earth: a "Supply" for the module electronics and dedicated test pulse outputs, and a "Load Supply" for the outputs. This separation allows for flexible power management and enhances system resilience. For instance, in applications where multiple machines are secured by common safety devices, the "Supply" can feed all modules and general safety devices, while each machine has a separate "Load Supply." This configuration enables individual machines to be switched off without affecting the safety devices or other machines, or ensures all machines are safely shut down if the general "Supply" fails.
The inputs are designed to detect "High" signals (24 VDC, +15 to +30 VDC) and "Low" signals (0 VDC, -3 to +5 VDC). To ensure reliable signal detection, a signal must be present for a duration longer than the configured Event Timeout in the PSS WIN-PRO system software. Signals shorter than 500 µs are ignored to prevent spurious event telegrams. The module offers two signal change behaviors: "Default," where only the first signal change is registered until an acknowledgment telegram (ACK) is received, and "Fast," where each signal change is stored in a FIFO telegram buffer, allowing for multiple event telegrams to be sent upon ACK reception.
The 8 digital outputs include 6 positive-switching (Load Supply) 2 A outputs and 2 negative-switching (Ground) 2 A outputs. The positive-switching outputs are suitable for resistive and inductive loads up to 2 A, with an integral discharge circuit also supporting capacitive loads up to 1 µF. The negative-switching outputs are also rated for 2 A resistive and inductive loads but are primarily intended for non-safety-related applications when used individually. Two dual-pole outputs can be configured by combining a positive-switching output with a negative-switching output. All outputs are protected against short circuit, overload, and excess temperature.
For safety-related applications, test pulses are crucial. The two dedicated test pulse outputs (T0 and T1) are fed from the module's supply voltage and are used to test the wiring of input devices. These test pulses are allocated to inputs via the system software configurator. Only inputs operating on the zero signal principle (switching off) are permitted for safety-related applications with test pulses.
The PSS SB DI8O8 is configured via the PSS WIN-PRO system software, where its device address is set, and I/O groups are defined. The module can be divided into Section A and Section B, which can belong to different I/O-Groups. Outputs always belong to Section A, while inputs can be assigned to either section based on a configurable limit value. This flexibility allows for tailored I/O management within complex safety systems.
The module's status is clearly indicated by a series of LEDs. Yellow LEDs show the status of individual inputs, lighting up when a "1" signal is present. Green LEDs indicate the status of outputs, illuminating when a "1" signal is present at the output. Additionally, dedicated LEDs provide overall system status:
For applications requiring high safety categories (e.g., Category 4), dual actuators must be connected to two different outputs, and a feedback loop should be used. The module's outputs are periodically switched on and off to test the output transistors and monitoring circuits, ensuring their proper function. Outputs can be excluded from these automatic tests through configuration, but in such cases, the user program must implement its own output tests to reduce fault detection time.
During commissioning, it is essential to perform an error simulation for every safety-related positive-switching output. This involves setting the output to "1" (indicated by its LED lighting up) and then generating a short circuit between the output and 24 V. This procedure verifies that the output test, whether automatic or user-programmed, is effective and that no output has been incorrectly excluded from testing.
The module is designed for easy installation, attachable to a 35 mm DIN-rail or screwed onto a mounting plate. If attached to an earthed DIN rail, the module's functional earth requirements are automatically met.
When recommissioning the device, a full function test is recommended, especially if terminal blocks have been reinserted, as they are not designed for frequent exchange. This helps eliminate potential errors that might arise from such actions. In case of a module defect or wiring error, the system provides clear diagnostic information through error telegrams stored on SafetyBUS p and in the module's error buffer, which can be accessed via the PSS master's display and the system software's error stack. This facilitates quick identification and resolution of faults.
General| Supply voltage | 24 V DC |
|---|---|
| Width | 22.5 mm |
| Protection Class | IP20 |
| Product type | Safety relay |
| Auxiliary contacts | 1 N/C |
| Terminal type | Screw terminal |
| Standards Compliance | EN 60947-5-1, EN 60204-1 |
| Operating Temperature | -20°C to +55°C |
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