Gas detector Principle | Gas detector Logic

DCS SIS
1

Gas detectors is installed in the platform according to the type and nature of perceived hazard.

Gas detector Principle

For example, IR point type gas detector only measure flammable gas concentrations at certain points and there is no way of knowing the composition of the gas cloud between the point detectors, it is therefore necessary to initiate alarms and executive actions well before the concentration at any point reaches 100% of the LFL.

The settings shall be as follows:

· High level gas (process areas) – 20%LEL,

· High-High level gas (process areas) – 50%LEL,

These type of detector usually have 7 signals and status that are shown in the control room,

  1. Faulty Status

  2. Calibrate alarm

  3. High gas alarm

  4. High gas exec action

  5. High-high alarm

  6. High-high gas exec action.

  7. Inhibit signal

The logic are:

  1. If the gas detector is in the faulty status (open loop or short). None of the other signals will be executed until the reset command is activated.

  2. If the gas detector is in the inhibit status. None of the other signals will be executed until the reset command is activated.

  3. High alarm and high-high alarm and trip action will always present until reset signal is executed,

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