The present invention relates to measuring systems and a method for operating a measuring system for detection of wire breakage in measuring systems which measuring system based on the measured current or voltage measures the impedance of at least the first censor which measuring system transmit the result of the measurement of the impedance to a connected system. It is the object of the invention to be capable of detecting wire breakage and sensor failure in temperature sensor systems simultaneous with the temperature measurement. The object can be fulfilled by a system where the measuring system can comprise an AC current source, which AC current source generates an AC current, which AC current is transmitted through the wires, and through at least the first censor, which measuring system analyses changes in the phase angle between current and voltage of the AC signal. It is hereby possible that if the difference in the frequency of the signal affecting the impedance or voltage of the sensor, and the frequency of the injected wire testing signal is sufficiently high so that it is possible in the system, that receives the signals to distinguish between the first measuring signals and the second wire testing signal.