UV Sensor


Thread Starter

Aditia Hermanu

Dear sir...

I have some question about UV sensor for fire and gas protection system.
Are UV sensors sense radiation from radiography activity ?
If there is radiography activity near UV sensor, is it possible UV sensor sense the radiation signal and give a "fire signal".
How to solve this problem ?

Thank you

Aditia H

Hafeezullah K. Khan (MNT-J)

Dear Aditia,

We face similar problem in our plant. During construction of new plant near the existing one, the radiography and even the welding near boiler area effected the UV sensor of burners.

You can resolved this problem by providing the lead shielding around the UV sensor. The lead shield of 1mm thickness is enough for this purpose.

I think it will solve problem.

Thanks and Best Regards,

Hafeez Ullah Khan
Tel: 00966 3 3406508
Fax: 00966 3 3406577

Matthew da Silva

In answering your question about fire sensors, there are options that would be appropriate for fire detection systems. Fire detectors are
usually smoke detectors, since it is the smoke, normally, rather than the fire, which kills. Smoke detectors are designed to sense the existence of particles having a certian size and concentration in the air. Particles suspended in the air interrupt a light beam inside a photoelectric sensor. Photoelectric sensors of this type are used frequently but have a disadvantage in that they are slow to react.
Faster, ionization sensors are also single-unit installed sensors and they use a radiation method to sense particles. Their performance is compromised in environments where a lot of fine
particles are habitually present. Regular dust and stuff is OK, though.

Fires don't give off light (which UV is) so much as heat, which is infrared.

Hope this helps.
Matthew da Silva
Yamatake Corporation
Tokyo, Japan

Kent L. Gerhardt

The UV/IR (Ultraviolet/Infrared) sensors we use in petrochemical and oil/gas applications are very sensitive to X-rays and other sources of
spurious light. For instance, welding arcs and sunlight reflecting off of water or shiny surfaces can also trip most brands.

Operators soon learn to bypass UV/IR detectors anytime X-ray inspection or any source of electrical arcs are present. In addition, we find
that any pin holes or sources of light (like lightning flashes thru windows) must be prevented. We've even tripped the UV alarms when a door to a protected building is opened at the "wrong" time.

If anyone has found a brand/model that seems to be able to detect a real fire OK but is less prone to false alarms from these sources,
please share your experiences.


Kent L. Gerhardt

Kent L. Gerhardt
G&A Systems Group
P.O. Box 2062
Hammond, LA 70404 USA
voice: 504.542.1963
fax: 504.345.5475
I think you mean the radiography activity after the welding works. From my experience the UV that is generated by the welding arc works next or
around are capable to trigger the detection system since they almost have the same wavelenght.
Since those works are temporary and normally monitored localy by the operators, the UV dectection system can be overidden during the task. You may want to find the override procedures before do the UV override, work
permit, etc, etc. In case of genuine fire in the machinery being protected by the UV system
during the above activities, the operator can always remove the override to stop the machine.
Hopes this helps.
Jose Chong
Field Instrument Eng.