The Orbis Intrinsically Safe (I.S.) Heat Detector range incorporates seven heat detector classes to suit a wide variety of operating conditions in which smoke detectors are unsuitable.

Orbis I.S. Heat Detectors have an open-web casing which enables air to flow freely across a thermistor which measures the air temperature every two seconds. A microprocessor stores the temperatures and compares them with pre-set values to determine whether a fixed upper limit – the alarm level – has been reached. In the case of rate-of-rise detectors the microprocessor uses algorithms to determine how fast the temperature is increasing.

Static heat detectors respond only when a fixed temperature has been reached. Rate-of-rise detectors also have a fixed upper limit but they also measure the rate of increase in temperature. A fire might thus be detected at an earlier stage than with a static detector so that a rate-of-rise detector is to be preferred to a static heat detector unless sharp increases of heat are part of the normal environment in the area protected by the heat detector