A device and a method for determining the magnetic field strength of an electromagnet is illustrated and described. The object to provide a device and a method for determining the strength of the field of an electromagnet, which allows even minor changes in the magnetic field to be determined quickly is achieved in terms of an apparatus by a device having a measurement device for determining the magnetic field of the electromagnet, a low-pass filter element which is connected to the first supply line and to the second supply line and is adapted to emit a signal at the output of the low-pass filter element from the voltage between the first supply line and the second supply line, which signal approximates to the time profile of the magnetic field strength in the electromagnet, having a low-pass filter downstream from the measurement device, having a high-pass filter connected in series with the low-pass filter element, and having a signal output, wherein the output of the measurement device and the output of the low-pass filter element are connected to the signal output.