Frequently asked questions


Flame monitors are safety-related components for the observation of flames in diverse industrial combustions. They indicate in a very safe way whether the flame of a specific burner is burning or not.
A flame monitor consists of a flame sensor and a control unit. If both components are space-saving combined in one housing it is also called a compact flame monitor. Depending on the dimensioning of the burner geometry and ambient conditions a compact flame monitor or separate flame sensor can be mounted to the burner plate or boiler. For separate flame sensors the control unit is often installed in a control cabinet located in a central spot of the facility.
Sometimes flame monitors or flame sensors are also called flame scanners.

For challenging environments (high temperatures, limited space) we offer flame monitors and flame sensors which can be equipped with fibre optics. In that way it is possible to gather information of flames in the boiler and to transmit the flame signal to the flame sensor that is located in distances up to several meters.

Beside our wide range of flame monitors and flame sensors we suggest some accessories to guarantee a technically perfect installation.

Several adapters are available to find the best fit for existing sighting tubes at the boiler or burner plate.

Insulators create a thermal and/or electrical separation between flame sensor and sighting tube.

Swivel mounts enable the flame sensor to have an optimized alignement in order to see the flame properly.

In addition a ball valve can be installed to close the sighting tube and thus to prevent the flame sensor from damage. It's recommended when removing the flame sensor at increased furnace pressure.

An optical adjustment aid helps to align the swivel mount. Instead of the flame monitor the adjustment aid is fastened to the swivel mount by the coupling nut. The inspection glass of the adjustment aid allows the technician to locate the flame inside the burner with the naked eye and thus finding the optimized position of the swivel mount. Once the swivel mount is tightened the re-attached flame monitor will have the identical angle of view into the boiler.

To guarantee an optimized flame monitoring it is important not only to have the best suitable device but also to provide a professional installation. The correct position at the burner plate and the use of specific choosen accessories is essential.

Thus we recommend to mount a swivel mount to get the most flexibility to adjust the viewing angle of the flame monitor. The highest goal is to get the best view on the flame through the sighting tube. Unregular geometries at the burner plate or sighting tube can also be compensated by using a swivel mount.

Another critical point is the dimensioning of the purge air system. Referring to given recommendations and conditions of the boiler the purge air volume and pressure has to adjusted in a way that the optical unit of the flame monitor is shielded any time from any contamination and damage.

For monitoring flames in explosive environments we offer our well approved and tested solutions as specific designed constructions. All explosion prooved housings and connectors meet the required standards; our certificates and production processes are subject to regularly inspections of national and international product safety certification organizations.

All questions for your specific application will be answered by our sales engineers and product managers.

SIL - Safety Integrity Level

Our compact flame monitors D-LX 200 and D-LX 720 were the first compact flame monitors worldwide with a complete SIL3 certification according to IEC 61508, parts 1 to 7. Holding this certificate we guarantee to fulfill all requirements to meet this high standard of safety.

A complete certification that includes all parts of the standard covers possible probabilistic errors like faults in the hardware but also potential systematic errors. Because of this it constitutes a special seal of quality for the development process. Retroactive error calculations according to parts of the IEC 61508 usually neglect a part of the possible device errors.


It is DURAG GROUP’ s policy to realize repairs, delivery of spares and wear and tear parts for a period of 10 years after the date of discontinuation.

  • We do interpret as date of discontinuation the year of last publishing in our customers price list for regular sales.
  • It is likely that such discontinued unit has been delivered the year after discontinuation because lifetime of projects requires the same.
  • The time interval is not extended if units had been delivered later than the date of discontinuation.
  • Our stocking of spares takes into account that major repairs of units being older than 15 year are normally not economical.
  • Please take into account that it might be true that not every part of a unit is classified to be a valid spare part.
  • We cannot guarantee to deliver a complete unit as spare over the mentioned period of time. Even if we had delivered a complete unit as spare after the date of discontinuation the interval of keeping spares on stock is not extended.

If you are interested in the date of discontinuation of your device please contact us.

D-FL 100 DS is a MPPT (multipoint pitot tube), which uses the impact pressure measurement method.

The method is very accurate however at low flow rates, the measurable pressure difference is very small. As a result, the measured threshold is determined by the uncertainty of the differential pressure transmitter.

Basis of D-FL 100 is a specially designed probe with two measuring chambers, each equipped with several bores.

The measuring chambers are pneumatically separated from each other.
The measuring chambers are connected to a differential pressure transmitter.

The probe generates a differential pressure in flowing sample gas dependent on:

  • V  the flow velocity of the gas
  • R  the normalized density of the sample gas
  • T  the sample gas temperature
  • P  the absolute pressure of the sample gas.
  • K1 the flow profile of the sample gas in the flow channel
  • K2 the probe profile
  • K3 the arrangement of the port openings

DURAG offers a precise differential pressure transmitter as an option to the probe. The selected transmitter has a basic range of 0-10 hPa and can be set to a minimum output range of 0 to 0.5 hPa corresponding to 4-20mA output .

Ex works the transmitter is configured to:

  • output the dP measured value square rooted.
  • suppress output values < 6% of the assigned mA output range (= 0.002 hPa at 0.5 hPa).

The zero suppression can be parametrized different or disabled. For special applications DURAG configurates the zero suppression to 3% (= 0.001 hPa).
As a result of this supression function of the dP transmitter those measuring gas flows, which produce a differential pressure signal, which is smaller than the threshold are indicated as 0 m/s (= 4mA). Consequently the setpoint of the threshold determines the minimum detection limit of D-FL 100. The detection limit of a D-FL 100 typically is a function of the measured gas temperature as follows:

values valid for 6% (3%) threshold of zero suppression

  • Gas velocity 0.4 (0.3) m / s at T =  20 ° C
  • Gas velocity 0.5 (0.3) m / s at T = 100° C
  • Gas velocity 0.5 (0.3) m / s at T = 200° C
  • Gas velocity 0.6 (0.4) m / s at T = 300° C
  • Gas velocity 0.7 (0.4) m / s at T = 400° C
  • Gas velocity 0.7 (0.4) m / s at T = 500° C
  • Gas velocity 0.8 (0.5) m / s at T = 600° C

These detection limits depend on the principle but are no special property of D-FL 100!

Measured values higher than the listed detection limit are precise, because the measurable difference pressure of the probe is increasing quadratic with gas velocity.

The D R-220 is an optical Transmission meter. The internally measured parameter is transmission.

The physical range of D-R 220 is:

  • Transmission: 100 .. 2.5% T

this physical range corresponds to

  • Opacity: 0 .. 97.5%
  • Extinction: 0 .. 1.6 EXT

The 4-20 mA analog output of the D-R 220 can be assigned to customer requirements by help of DIP switches as follows:

  • 4-20 mA corresponds to 0 .. 25% OP
  • 4-20 mA corresponds to 0 .. 50% OP
  • 4-20mA corresponds to   0 .100% OP
  • 4-20 mA corresponds to 0 .. 0.2 EXT
  • 4-20 mA corresponds to 0 .. 0.4 EXT
  • 4-20 mA corresponds to 0 .. 1.6 EXT

D-ESI 100 configuration software also allows to assign any interval within the base ranges.


Please include the following information to the equipment which is shipped to DURAG

  • a short description of the malfunction
  • contact of your service technican (E-Mail / phone) who can help with additional information if neccessary
  • contact within DURAG GROUP who has previously been informed about the subject
  • contact in your company regarding commercial issues (cost estimate etc.)
  • we do not make use of RMA (return merchandise authorization) numbers

You can help us protect the health of DURAG GROUP employees at the receiving department or repair department when you consider the following:

  • Please clean the equipment prior to shipment if you assume that they might have been in contact with harmful substances.
  • This is especially true for process applications and for applications in raw gas.
  • In most cases applications behind exhaust gas cleaning systems do not require special treatment.

An explosion can only occur when flammable material (e.g. gas or dust), oxygen (e.g. from air) and an ignition source come together. Electrical and mechanical devices can be an ignition source and hence these must be protected if they are to be used in explosive atmospheres.

ATEX is a French abbreviation (ATmosphère EXplosible). It comprises of two European Directives for explosion protection. The Directive 94/9/EC (ATEX95) for manufacturers specifies the requirements for equipment which is used in explosive atmospheres. The directive 1999/92/EC (ATEX137) is for operators and defines safety measures for the concerned personnel.

Ex-devices have additional safety features to enable their use in explosive atmosphere without causing an explosion what could result in serious harm to people and damage machinery.

The European standards series EN 60079 which is identical to DIN 60079 (German national law) and IEC 60079 (international law) can be used to fulfill the ATEX directives. The standard EN 60079-0 is the general base norm for all EX-devices.

Notified Bodies are examination organizations which are nominated by the Government. They are authorized to approve EX-devices. They have laboratories to prove the safety protection for explosive atmospheres. The Notified Body issues an Examination Certificate after successful approval.

The safety features for some test devices which are representative of the series are examined according the standards EN 60079. An examination organization performs EX-relevant tests with test devices in a laboratory. At the end, a positive tested EC-Type-Examination will be attested by the examination organization.

There are different technical possibilities to prevent an explosion caused by devices in hazardous areas. The most popular methods are described in the standards EN 60079. The gas group (e.g. IIC), the temperature class (e.g. T6) or the max. surface temperature (e.g. T95°C) are part of the characterisation for a type of protection.

The likelihood of creating an explosive atmosphere can vary a lot. The separation of hazardous areas in different EX-zones describes the different potential danger of explosive atmospheres. EX-devices are marked for which EX-zone there are suitable.

The operator of a facility is responsible for the safety of the facility. The classification of hazardous areas is usually defined by an external EX-expert and detailed in an explosion safety document.

DURAG has six product (families) which have a type-certificate according to ATEX: D-LX100, D-LE 603, D-LX 200/720, D-GT 80* and D-FW 240 /Ex. ATEX certificates e.g. for the enclosure from other manufactures are used for some devices, e.g. D-HG 400 * Ex.

The TÜV Nord certifies the quality standards of DURAG's series production at the production site in Hamburg. It ensures that the safety features of all devices of the series are consistent with the test samples of the EX-Type-Examination.

EX-devices can only be repaired by the manufacturer or for EX-devices qualified experts. This is the only way to ensure the function of safety features after the repair.

ATEX certificates are valid in the European Economic Area. The IECEx is forseen for the global international markets and is already accepted in some countries like e.g. Australia.