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Air min. air pressure monitor (SIL 2, PL d)

The Air min. air pressure monitor described in EN 746-2:2010 subclause is designed to monitor the combustion air supply during the pre-purge, the burner start and the burner operation of the system. If the level falls below the set limit value, the system must perform a fault lock-out.

The air pressure monitor must be checked prior to system start-up to establish its “no flow” state. In the event of an error during the “no flow” state check, system start-up must be prevented.

Requirement as per EN 746-2


CO formation due to excess gas → explosion

Determining the required SIL pursuant to IEC 62061

Frequency & exposure duration Fr: < 1 per h to ≥ 1 per day; > 10 min → 5 points

Probability Pr: thanks to the downstream air deficiency cut-out on each burner (pneumatic ratio control system, pressure switch), the probability that a hazardous event occurs is rather low. → 2 points

Avoidance Av: the hazard can be avoided by regular maintenance and by checking the pressure switch for contact changeover pursuant to EN 746-2. → 3 points

Effects: death, loss of an eye or arm

Determining the required PL pursuant to ISO 13849-1

Severity of injury S: severe (usually irreversible injury including death) → S2

Frequency and/or duration of hazard exposure F: frequent to continuous and/or long exposure to hazard → F2

Possibility of avoiding hazard or limiting harm P: possible under certain conditions → P1

Enter details



Enter the calculated values in the adjacent “app” to determine the required safety level.

Select products






The required SIL and PL can be achieved with these products. The calculation (see below) provides verification of this.

Sensor: pressure switch for gas DG

Logic: protective system control FCU

Actuator: solenoid valves for gas VAS











The flowchart shows how the products are integrated into the application to achieve the required safely level.

Calculating the SIL, PL

Select products in the adjacent “app”. Depending on the product click on whether the function should have one or two channels and enter the demand rate per hour or per year.


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