Temperature measurement at evaporator outlet

A method for measuring temperature of the fluid at an outlet from an evaporator in a once-through boiler of benson type, which evaporator includes one or more inlet headers supplied with water which is passed on to evaporator tubes which communicate with a heat-transferring medium, wherein the water in the evaporator tubes is transformed into a fluid which may either be subcooled, saturated or superheated and which is then passed via evaporator stubs to one or more outlet headers of the evaporator, said method comprising the steps of:

• measuring the temperature of the fluid with the aid of temperature sensors which are placed on adjacently located evaporator stubs for a number of important and critical parts of the boiler;
• supplying the measured temperature values for each part to median value selectors, and
• supplying each median value to a maximum selector, to obtain the maximum temperature (t.sub.max) of some of the outlets from the evaporator and to a mean value generator to obtain the mean temperature (t.sub.mean) of the fluid at the outlet of the evaporator.