The generation and monitoring of a load-independent output current for a level meter, pressure gauge, flowmeter or evaluation device are described. A current that is equal or unequal to the measuring current, but inverted relative thereto, can be generated continuously or within certain time intervals in a switching circuit that is realized independently of the network generating the measuring current. The generated current can be fed into the measuring circuit at a comparison point and added. The compensation principle makes it possible to determine whether the measuring current corresponds to the nominal value, wherein a testing current is fed into the first electric circuit by means of a second switching circuit that contains a second current source. A certain expectancy value of a voltage to be tapped can be calculated in dependence on the testing current being fed in and the nominal value. If the measured voltage deviates from the expectancy value, a deviation of the measuring current from the nominal value is detected and can be output for a user.