How to set SLIO Safe Input Module Discrepancy Timeout
| Version Number | Description |
|---|---|
| 1.0 | Preliminary draft |
|
|
This will explain considerations for setting the discrepancy time with SLIO safe digital input modules when using 2-channel mode.
1. Supported Components
| Component Name | Version |
|---|---|
| iC9200 series | ≥ 2023.9 |
| iCube Engineer | ≥ 2023.9 |
2. Solution details
2.1 Background
When using safe digital inputs in a 2-channel architecture it is important to check for discrepancies in the states of both inputs to ensure that both safe digital input channels change state within an expected period of time (e.g. 100 ms). This can help detect fault situations such as:
- Wiring issues (e.g. disconnection, short, etc.)
- Welded contact
Note: Discrepancy timeout does not apply to 1-channel circuits.
2.2 Setting Discrepancy Time
When setting the Discrepancy Timeout safety parameter it is important to understand the characteristics of the input connections and devices (e.g. switches, relays, contactors, buttons, etc.) such as:
- Inherent delays between channels switching
- De-bouncing of contacts
These characteristics are best determined from:
- Device data sheets
- Direct measurement with an oscilloscope
The image below shows direct measurement of a 2-channel E-Stop button when it is being reset. Note that there is s distinct delay between when the (2) channels switch and there is also a period of debounce after both channels have switched. The Discrepancy Timeout should cover the total time from when the first channel switches to the end of the debounce period, which is approximately 15-16ms. To allow some headroom and for the simplicity of a round number, a 20ms or greater Discrepancy Timeout would be recommended for this example.
