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    Updated: 10 May 2020


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Petrol Vapors

Basics on gas monotoring

Harmful Gas
Gas monitoring of combustible gases serve to obtain alarm in case of gas leakage.

The density of the petrol vapors is < 1. (Air = 1,0)

Appropriate alarm levels can be determined from case to case, but outdoors, we recommend level 1 to 10% of LEL and level 2 to 20% of LEL.

Information on LEL och explosion hazard

Alarm level 1 should result in control measures while alarm level 2  should be regarded as an emergency alarm.

When forwarding alarms to local emergency services, we recommend using two detectors at alarm level 3 in order to avoid false alarms.

Alarm level 2 should result in flashlight and/or audible alarm at the object.

Flashlight should be used for alarm level 1.


Outdoor Gas Monitoring
Since recommendations on monitoring always depend on the circumstances in the various specific cases, one must always evaluate the effects of gas monitoring.

For detector placement consider the following:

  1. All pieces of equipment connected to the object that are considered to be potential leak sources inside buildings/sheds should be monitored.

  2. Sometimes special consideration must be taken to local residents or other factors where the slightest prescence of gas is undesirable.

Plants have sometimes been built so that not even strong winds could have prevented a certain accumulation of flammable gas around the alarm object.

The advantage of creating a special alarm area is that alarms from the gas monitoring unit can be obtained at a very early stage.

The disadvantage of creating a special alarm area is that explosive gas concentrations can build up in here. With no special alarm area, explosive gas concentrations might not develop.

Choice of Equipment

The Stand-alone detector Combi is a detector where power supply, alarm and control functions are integrated in the detector housing. This detector is used where very simple systems are sought and only few monitoring points are desired.

Analog detector APET, Wall















 Analog detector APET, Duct









Protection Manual





Gas alarm plate for gas detector
















OAW 24
Combined warning horn/flashlight 
for gas detectors
















OA 24













The multipoint system equipped with an instrument for gas monitoring is based on detectors providing a gas leak unit with a signal related to the gas concentration.

The signal is then processed in the gas leak unit where measurements, alarms and control functions are obtained.

The most common gas leak unit is of this type and the CGD model is used for several measuring points.

More here

Preferred system functions
Regardless of the type of gas leak unit you choose, we suggest a study of the following features:


Should the facility have one or two alarm levels per detector?

Control signals:

Should the facility have one relay per alarm level and sensor?
Should the relay have a function for time delay?
Should the facility have computer output?


Should it be possible to read alarm values?
Should it be a digital, an analog or a flashing sign for gas alarm?


Should the facility itself be able to identify sensor errors, open circuits and instrument errors?


Should the plant be equipped with a battery backup?

The exchangeable sensor X-CHANGE turns the recalibration into a home game:

  • Delivery of recalibrated sensor cartridges

  • Easy exchange, no specialized company needs to come to you

  • Available for every gas type

  • At guaranteed exchange prices

  • Increased reliability (SIL2-software)

  • Important time and cost savings

The X-Change support guarantees a price based on the consumption of the sensor capacitance.

For each uncalibrated sensor returned to AP, you will receive a credit for the unused capacity of the sensor.

More >

Legal and safety requirements
The devices are manufactured according to the regulations and various directives such as
EN 50545, etc.

Products delivered by AP meet and even exceed the new European Standard EN 50545.

The safety features check the connected warning devices on functionality and open circuit day and night (Level SIL2 according to EN 50271).


BPET, Field Bus detector - Wall
Modbus, BacNet, etc.



to do   BPET  








BPET, Fieldbus detector - Duct
Modbus, BacNet, etc.




Underst. Art &  




RS485 Science  
    Environm. Duct  
    declaration Kit  



Gas Leak Unit, CGD

Gas Leak Unit









Quick and easy replacement of sensor


  1. Open the housing with a screwdriver.

  2. Disconnect the sensor cable and unscrew the disused sensor head.

  3. Exchange the sensor cartridge (3) and connect the cable of the new sensor head to the PCB.

  4. Close cover of the housing with the screws (1). The recalibrated sensor is ready for use at once.





Electrical products in an explosive environment
A small amount of energy - a flame, spark, high surface temperature or similar is required to ignite an explosive gas mixture.

Products installed in an area with a potential explosion hazard must of course in themselves  not be a potential explosion hazard.

For this reason, the products are manufactured in such a way that this cannot occur.
The equipment must also be labeled and tested - ATEX classified - by the approved testing authority.

The Ex-class information is available in "Swedish Standard"
The choice of which Ex-classification is required is determined by factors such as type of gas, permissible maximum surface temperature and potential explosive hazards in the area where the products are to be installed.

The potential explosion hazard in the different areas is determined by the zone classification according to "Swedish Standard".

More about ATEX-products can be found in the following link

ATEX explosionproof detectors

Combi detector CPET - Wall
ModBus, Analog, Relay Output




Underst. CPET  

declaration RS485 RS485 Datasheet  





Combi detector CPET - Duct
 ModBus, Analog, Relay Output




CE missing  











E-mail: lars@fjellcom.se     

Phone: +46(0)31-287202

Mobile: +46(0)706-755561



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