Where fixed detectors should be used &where rate of rise detectors should be used?

Question

they are used in fire fighting&fire detection systems

Answer 1

The rate-of-rise detector ignores steady state temperature, and responds only to steep rates of temperature rise.  At a rise of 15 degrees per minute, it should operate within two minutes.

A fixed temperature detector operates when heated to a specific temperature, such as 140 degrees F.  Rate-of-rise detectors operate faster than fixed temperature, when the ambient temperature is much less than the rated temperature of a fixed temperature detector.  For example, on a 50 degree day, and with a 15 degree per minute temperature rise, the rate-of rise-detector might operate at 80 degrees.  The fixed temperature detector would not operate until the temperature reached its operating temperature.

Fixed temperature detectors are best when normal temperature rises (such as sun load, heat process or building heating) are at a high rate.  Otherwise, rate-of-rise is usually best.

Answer 2

Fixed detectors monitor normal temperatures say 30c.

  Rate of rise would detect the increasing temperature of a progressing fire.