Sensing and monitoring apparatus

摘要

There is described a monitoring apparatus comprising at least three sensors capable of detecting a characteristic of a fluid, the sensors located within a fluid to be monitored; each sensor comprising a probe arranged to enclose a temperature sensing device; a power circuit including a first current source, a second current source and a third current source, the first current source connected to a first temperature sensing device, the second current source connected to a second temperature sensing device, the third current source connected to a third temperature sensing device, the first current source and the second current source arranged to power respective first and second temperature sensing devices so as to cause self heating of the first temperature sensing device and the second temperature sensing device to a first temperature; the third current source arranged to power the third temperature sensing device so as to cause a minimum self heating of the third sensing device to a second temperature; wherein the first temperature is a higher temperature relative to the second; a sensing circuit connected to each said sensor, each circuit comprising a member arranged to compare the voltage across a temperature sensing device and to output a signal indicative of a response of the probe of the temperature sensing device, a first comparator and a second comparator and a comparison circuit for comparing the response of the second temperature sensing device with the response of the first temperature sensing device and adapted to output a second compare signal, and an output circuit adapted to receive a test signal and comprising means for indicating the characteristics of the fluid to be monitored.