Read E015-0 Negacoax text version

Sensing the hot point with the NEGACOAX overheating detector

from vision to reality


NEGACOAX is a specific family of sensors based on the measurement of the insulation resistance and the melting point of a specific eutectic salt. When the melting point of the salt is reached, the resistivity of the salt varies suddenly and a short circuit occurs in the detector. There are different versions of NEGACOAX available for a range of industrial applications. The one in particular we are illustrating here is the NEGACOAX® RI. This type of sensor is used for the early detection of overheating and fires on aircraft, and is available for a range of alarm temperatures.

Sensors in environmental control system (ECS) compartment

Sensors in the engine pylon Sensors in APU compartment

Sensors for bleed air leak detection

Sensor construction

NEGACOAX® sensors consists of an outer metallic sheath, a central conductor, insulated from the sheath by a ceramic insulator impregnated with an eutectic salt. The central conductor is selected and adjusted to meet the requirements of the electronics system (from 1.0 ±0.2 W/m up to 15.0 ±1.0 W/m). The eutectic salt is carefully selected so that its melting temperature corresponds to the specific temperature required to activate an alarm. We can offer detectors for the following alarm temperatures 104°C, 124°C, 204°C, 232°C, (i.e. 220F, 255F, 400F, 460F respectively). The triggering of the alarm temperature is based on the melting of the eutectic salt which occurs when this temperature is reached. The eutectic salt melts and the insulation resistance decreases sharply, generating a short-circuit between the conductor and the sheath which can be measured with appropriate electronic equipment.

Insulator impregnated with eutectic salt Central conductor

1,00E+10 1,00E+09 1,00E+08 1,00E+07 1,00E+06 1,00E+05 1,00E+04 1,00E+03 1,00E+02 1,00E+01 1,00E+00

Outer sheath

As the temperature returns to normal, the eutectic salt solidifies returning to its original state. This is a non-destructive process, and the sensor can be reused provided the maximum allowable temperature has not been exceeded. The graph represents 10 detection cycles and illustrates that the sensor has retained all its original properties over the 10 cycles.











Many line resistances and/or tolerances values are also possible. For other alarm temperatures many possibilities are offered. (80°C-176F, 154°C-310F, 195°C-385F, 280°C535F, 302°C-575F, 415°C-780F, 425°C-800F are also available.



Electrical characteristics

The IR vs temperature curve becomes extremely steep as it approaches the alarm temperature. The accuracy of the alarm temperature is +/- 5 % when the sensor is controlled by an adequate controller. Measurement of the insulation resistance is effected by alternating current (ac) as direct current (dc) could polarize the eutectic salt and thereby alter the properties of the sensor.

Dimensional characterisics

Cable diameter: 1.8 mm (.70"). Our manufacturing process ensures extremely high compaction of the insulating powder, resulting in an almost solid wire which effectively resist vibrations, thermal shoks and aging. Even bent on small radius (25 mm - 1"), the central conductor will never touch the outer sheath creating a short circuit. Additional benefits are good heat dissipation and fast response times. The length of the sensor will vary according to its application and it is possible to supply lengths up to 5.2 m or more.

Note: the length is measured at the ends of the connectors when placed on an extended position.


All connectors fitted to the cable are compatible with most sensor connectors available in the market. They are also compatible with both existing mounting brackets and interconnecting hardware. A customized connector is available fitted with a spring which facilitates mounting on site and maintains the mechanical strength of the sensor.

1.00E+05 1.00E+04

IR in ohm

1.00E+03 1.00E+02 1.00E+01 1.00E+00 110 115 120 125 130 135 140

Sensor extension cable

T in °C

A coaxial extension cable can be supplied with either a male or female connector for connecting to the electronic monitoring equipment.

l Line resistance at room

temperature: from 1.0±0.2 oh:s/m up to 15.0±1.0 ohms/m can be adjusted according to your specifications l Insulation resistance under 1kHz - 1V, alternating current : the IR resistance values depend of the detector chosen. For example, a detector required for an alarm temperature of 124°C : l at 20°C (68F) IR 20 M l at T= 124°C ± 5 % (255F) IR 20 .m


The following points illustrate the care that must be taken when mounting or handling the sensors. »The sensors must be stored in their original packaging (polyethylene bag) and kept in a dry place until they are ready for use. »Do not use any lubricants on the connector threads or expose them to contamination of any kind. »Do not apply a DC voltage to the sensor to measure the insulation resistance between the sheath and the conductor, it can damage the sensor permanently. »Avoid bending the sensor cable at distances less than 50 mm ( 2") from the connector. »Do not apply any mechanical load or fixing when mounted

80 mm

38 mm 56 mm

9.5 mm

Guidelines for mounting

The minimum bending radius must not be less than 2.5 cm (1") The detector must be properly fitted with appropriate mounting hardware. The distance between two fixing points must not be too large in order to provide a correct support for the detector (10 to 12 cm / 4 to 5").



from vision to reality

40 years' expertise in mineral insulated cable technology.

In order to merit the confidence of our clients and satisfy their needs, the THERMOCOAX attitude is simple: to foster a trusted partnership with its customers. To ensure that this task becomes reality, we learned how to adopt to work within the constraint of very stringent applications as commanded by our customers. Our success is based upon the competence of our staff. Consisting of highly qualified in-house specialists, having at their disposal, equipment that are at the leading edge of technology, they will offer you professional advice and full technical assistance at every stage of your project. Within this team, for close collaboration you will be assigned to a project co-ordinator who will ensure from start to finish that the development of a product or an application, adheres to your exact requirements

To get your design off the page, we

Listen to your projects and understand as well as help to define your requirements, Study solutions that are best suited to your needs, Propose solutions compatible to your budget, Develop specific products still bearing in mind their future adaptability, Manufacture in accordance with the most stringent quality standards and precision rules, Deliver swiftly products, high quality

Full product range

Heating Devices Heating cables and elements Thermometry Temperature sensors Signal Transmission Mineral insulated cables Measurement and detection Specific sensors

Provide your technical team with support and assistance on a daily basis.

Data subject to alteration without notice - NEGACOAX ­ E015-0 JULY 01


Sce Commercial - Commercial Dept : 40 Bd Henri Sellier F 92156 SURESNES Cedex Tel.: +33 (0)1 41 38 80 50 Fax : +33 (0)1 41 38 80 58 http : // e-mail : [email protected] Siège Social - Head Office : Planquivon 61430 ATHIS DE L'ORNE France

THERMOCOAX S.A.S. au capital de 457 500 Euros

RCS CONDE s/NOIREAU B 323 459 925 - N° TVA / VAT Nr : CEE FR 32 323 459 92

EUROPE BENELUX Tel : +31 40 295 95 58 Fax : +31 40 255 54 78 FRANCE Tel : +33 (0)1 41 38 80 50 Fax : +33 (0)1 41 38 80 58 GERMANY Tel : +49 40 67 960 230 Fax : +49 40 67 960 333 UK Tel : +44 (0)1638 667 771 Fax : +44 (0)1638 666 162

REST OF EUROPE Tel : +33 (0)1 41 38 80 72 Fax : +33 (0)1 41 38 80 52 ASIAN PACIFIC AREA Tel.: +33 (0)1 41 38 80 63 Fax : +33 (0)1 41 38 80 52 USA Fax : +1 678 947 4450 Tel.: +1 678 947 8711 Or send your e-mail at [email protected]


E015-0 Negacoax

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E015-0 Negacoax