For the control of refrigeration systems it is many times necessary to evaluate information from the refrigeration system. This information involves primarily temperature information. Possibly, however, one also wants to evaluate other information about pressures or the cooling medium—or air flows. Occasionally, information is also obtained indirectly, for example a pressure information from a temperature information. Such informations do not, however, serve only for the control of the refrigeration system, but also to recognize faults at the earliest possible time; that is so early that the goods cooled are not damaged. It is also beneficial to have a detection made at a point of time at which indeed no significant temperature increase has as yet set in, the refrigeration system, however, having become heavily loaded by a non-optimal operation.
The signals in a refrigeration system change only relatively slowly. It is therefore difficult to recognize a trend if the signals move in a range from which a fault could be indicated. Since the signals are determined by sensors which evaluate the involved physical values at predetermined points of time, or a permanently created signal is only sensed at predetermined times, it often happens that a signal course has a “high-frequency” curve shape, that is the average value of the signal in fact represents the physical value to be detected. The value is, however, partially represented by considerable bursts upwardly and downwardly, which further aggravates the evaluation. This is especially true if the signal is arrived at by a differential forming condition, especially by a temperature differential across a heat exchanger. The term “high frequency” is here naturally meant in a relative way. The frequency is high as measured against the speed of change of physical values, such as the temperature in a refrigeration system.
The invention has as its object to be able to detect a fault at an early time.