🛑 Safety Voting Logic Explained Simply (SIS / ESD Systems)

In safety systems, voting logic determines when a shutdown should occur based on signals from multiple sensors.
The goal is to balance Safety and Plant Availability ⚙️.

Here are the common voting logics used in industry 👇

🟢 #1oo1 Voting Logic (One out of One)
➡️ Trip occurs if 1 sensor detects danger

⚡ Fastest response
🔧 No redundancy
⚠️ Sensor failure can cause false trip

🟢 #1oo2 Voting Logic (One out of Two)
➡️ Trip occurs

🛑 We talk a lot about #1oo2 and #2oo3, but most trips in plants still run on simple 1oo1 logic.

📖 Plain language:
1oo1 = “one out of one” must act to #trip.
You have a single sensor/input. If it goes into trip condition, the logic trips. No second opinion.

📍 Where you see 1oo1:

🔹 Basic permissives and #interlocks
⚙ Simple trips on PLC/DCS
🟡 Low-risk shutdowns
🛡 Sometimes in SIS/ESD for non-critical or low SIL demands

⚡ Behavior with a single #sensor:

✅ Sensor healthy + process safe →