A zigzagging thermocouple reading on a profile graph indicates loosely attached thermocouples. Other parameters that are determining sensor properties are the electrical characteristics of the thermocouple. This temperature difference is measured using a thermocouple. Adding more thermocouple pairs in series increases the magnitude of the voltage output. Even a sheath of magnesium oxide insulating the thermocouple will not keep the hydrogen out. The thermocouple temperature is limited also by other materials used. A common error in thermocouple construction is related to cold junction compensation. Although very little current flows, power can be generated by a single thermocouple junction. This reduces the emf output, and the thermocouple reads low. A thermocouple produces small signals, often microvolts in magnitude. The standard configuration for thermocouple usage is shown in the figure. The cheapest and easiest is a single thermocouple placed somewhere in the airstream. The table below describes properties of several different thermocouple types. Such "water cycle" can lead to erosion of the thermocouple and eventual failure. They can be almost as durable as a thermocouple.