Heat Detectors

S

Thread Starter

SHChaudhry

We are using AUXITROL heat detectors. The triggering point (value Deg C) is different during calibration by different technicians for same detector.

I would like to know, is it RoR OR Thermostatic type and what is right procedure of calibration OR testing of these heat detectors?
 
Ir you are referring to switches used for detecting the presence of a fire, these are usually very special switches. They not only trip on magnitude, they will also actuate when the rate of temperature rise exceeds the setting of the switch (and this particular setting is not usually adjustable like the magnitude is).

This is the usual cause of "calibration" problems. One tech will increase the heat faster or slower than another, and the rate-of-rise capability may actuate the switch before the magnitude setpoint is reached.

Most "heat" (fire) switch detector manufacturers have special testing/calibration equipment. When testing/calibrating these kinds of switches, sometimes it's best to have an outside fire protection company come in with the proper equipment to perform the desired testing. It costs a little more, but, then, how much time (and money) have you spent trying to achieve repeatable results on this exercise?

If you want to know specifically what characteristics your heat (fire) detectors have, you should consult the manufacturer's data sheets.
 
This is a very good question, and one I have been involved with recently. Before I go into too much detail, I'll state that my Unit is a GE 9FA STAG, so the Fire Protection System design, operation and specification will be different.

In the past, our Heat Detectors were subjected to a very crude "function test", by applying heat from a small blow lamp / torch, eventually the Detector changed state and the "FIRE" alarm was generated on the CO2 Fire Suppression Control Panel, or the torch operator gave up and drew the conclusion that the detector was not working and required replacing. With this "method" a) the temperature at activation is uncontrolled and unknown, and b) uncontrolled and unknown application of the heat from the torch was probably damaging the heat detector, shortening its life. Rather than turning the flame down and allowing an adequate response time. This was also the conclusion of the Heat Detector OEM, Kidde-Fenwall. The major issue would be that the Heat Detector may fail to operate in anger in a genuine fire situation, between tests, because of the over-exposure of heat during the tests, shortening the life of them.

Now I am looking to implement a new method of testing. What I plan to do is purchase a complete spare set of Heat Detectors, and function test them all in a Dry Block Calibrator, to ensure they are activating at the correct setpoint within the manufacturer's tolerance. Much more controlled, measurable and traceable. Come Outage, remove all the Heat Detectors from GT Enclosure and #2 Bearing Tunnel, and replace with the previously-tested spares. Noting of course the Detectors in different locations have different setpoints. To ensure adequate re-connection, a loop check is to be made on each Detector post installation. All the removed Heat Detectors will then be function tested using the Dry Block Calibrator, and if OK, be kept ready for re-installation at the next Outage. Any ones out of specification will be disposed of, and replacements sourced, and tested before considered fit for service.

This may sound long winded, but trust me, holding up a Dry Block Calibrator, in #2 Bearing Tunnel, with trailing 110v leads, whilst trying to monitor the contact state with a multimeter isn't the easiest task!

The fact that different technicians are obtaining different results is interesting..are they all using the same controlled testing method? How different are the results? Are they using the same test equipment? If the Detectors are anything life a Frame 9 then there are different setpoints for separate locations.

If the differences are fairly small, it may be within the repeatability specification of the Detector.

CSA - I read your point regarding Rate of Rise with interest. In the GE Device summary for our site, each Detector is given a temperature at switch activation, +/- accepted tolerance, but there is no value stated for Rate of Rise. Is the Rate of Rise function reasonably new, and found witn newer GE machines or has it been around for a while?

Thanks.
 
Mellberg,

It's a characteristic of the heat switches that are used. GE typically supplied Fenwal heat switches, and again, the rate of rise characteristic is not adjustable. It's a characteristic of the switch, and it's why special testers should be used.

I'm sure that EU restrictions have caused them to use something different (other than Fenwal make) these days in units shipped outside the USA.
 
S
Thanks for your explanation... FYI, All the technicians are using the same controlled testing method. Differences in results for the H/Detectors from Auxiliary compartment for GE frame 6B machine, tag 45FA-1A/1B/2A/2B are as follow: 391/405/393/330, with the same test equipment.

I'd personally tried (45FA-1A) to test the H/Detectors by raising the temp by 10~15 Deg C in steps (after 300 DegC) until NO contact becomes Close at 393 and then cool down the H/Detector and expose directly to 370 Deg C but didn't trigger the contact till temperature increased to 405 DegC.

Our H/Detector's specs are as follow.
AUXITROL, LE1 REGL 316 NO. I don't have the Vendors brochures for the said detector, pl do pass if you have one.

If I'm not wrong, the triggering point is 316 DegC with range of +9 DegC.

Regards
 
Top