Abstract: A method of determining the presence of scale on a water heating element (12), the method comprising comparing signals indicative of heating element temperature to determine whether the compared signals indicate a temperature decrease (44) greater than a predetermined value during a predetermined time interval and determining the presence of scale if the indicated temperature decrease is greater than said predetermined value.

Abstract: An apparatus and method are provided for detecting presence in gas of transient particulate above its normal zero or acceptable level within a duct (4), said apparatus comprising at least one emitter (2) of illumination selected from infra-red, ultraviolet and visible radiation capable of being projected over essentially the entire cross section of the duct (4) and at least one detector (8, 18, 25) for detecting any sparkle of the illumination from the particulate. The apparatus and method are in particular useful for detecting monitoring particulate in areas where build up or presence of particulate can be disadvantageous, for example hospitals and electricity generating stations.

Abstract: An apparatus and method are provided for detecting presence in gas of transient particulate above its normal zero or acceptable level within a duct (4), said apparatus comprising at least one emitter (2) of illumination selected from infra-red, ultraviolet and visible radiation capable of being projected over essentially the entire cross section of the duct (4) and at least one detector (8, 18, 25) for detecting any sparkle of the illumination from the particulate. The apparatus and method are in particular useful for detecting monitoring particulate in areas where build up or presence of particulate can be disadvantageous, for example hospitals and electricity generating stations.