rate of rise detectors

[kurnal]

I have been investigating an pre- fire signal from a Gent  SQuad detector in the floor void of an IT suite which is a  controlled environment. The under floor area serves as a plenum for the air conditioning and the unwanted pre-fire signal occurred at the same time as a fault on the air conditioning, with a sudden fall in temperature of several degrees. There is no evidence of a rise in temperature in the period following the sudden fall.
Is it possible for a gent SQuad multi sensor detector to report a pre-fire due to a sudden  fall in temperature?

[Graeme]

I would have thought it would be due to a rise in the temperature.
If the detector was set at  a very low threshold when the air con was running then when it failed it could have gone into pre alarm.

Don't do Gent but have never heard of any other due to drop in temperatue.

[Ark Angel]

Hi Kurnal,

You don't say what type of S-Quad it is (There are several different varients). However I would say that the fall in temperature was not the cause of the alarm. S-Quad devices do not pick up falls in temperature. Some varients also have dual angle technology to stop false alarms. To get a more definitive response you would need to know the type of sensor and state it was set to.

[kurnal]

Thanks
The default setting was state 0 but I dont have the model number to hand.

The fire prealarm occurred several minutes before the BMS reported a low temperature alarm. The room temperature curve is constantly monitored and flat until the sudden dip as the air conditioning malfunctioned. The dip almost coincides with the fire pre alarm.   It may be that the detector has a fault- it has given no problems over the last 18 months. The engineer reset it to state 5 but I think I would be happier if it were replaced.

[John Webb]

You don't say exactly what caused the air conditioning to fail. If it was an electrical fault, could it be that the detector responded to a short burst of smoke from the failing/failed electrics? The fact that this was picked up prior to the BMS reporting a problem makes this a feasible solution.

[kurnal]

Thanks John
It appears the failure was due to a thermostat control system failure but this is still being investigated by the air conditioning people. The pre alarm signal to the fire alarm was definately reporting a temperature rise- which there wasnt. Just a fall. I was just unhappy with the proposed fix effectively disabling the rate of rise function of the detector so I poked my oar in.

[John Webb]

Your comments noted, Kurnal. I know nothing about the internal circuitry of that particular detector, so cannot offer any further suggestion.

[FireFly40]

Hi Kurnal
 I recently had a problem with S4 detector in hotel bedroom when the aircon heater was on heat mode. It was firing the heat channel of the S4 det. Setting it to state 5 sorted the problem. I think all the S4 range of states involve some sort of rate of rise with a max fixed temp. It may be that the rate of rise deltaT also works in reverse or if the room got colder and then leveled out the detector may interpret the leveling as a rise.(my brains hurting now) Next time I play with a vig Ill stick an s4 in the freezer and see what happens
watch this space

[FireFly40]

Just to add the to the above comments if anybody plays with S4 states remember they are different to 34K states

[kurnal]

Thanks firefly40. An interesting thought. Be interested to hear what happens. And what the Missus makes of it.