Scanning unit for scanning a measuring standard

A measuring device for taking positional measurements of two assemblies which are movable in relation to one another, comprising:

• a measuring standard including a coded track formed by a graduated scale and a reference mark system;
• and
• a scanning unit, including:
• a detector system configured to scan the coded track;
• an additional detector system configured to scan the reference mark system, the additional detector system including a signal-sensitive surface configured to receive scanning signals when scanning the reference mark system, the additional detector system including at least two sensors, the additional detector system configured to use only one of the at least two sensors to scan the reference mark system during operation of the scanning unit;
• a differential amplifier including two inputs, each of the sensors connected to a respective one of the two inputs;
• and
• an arrangement configured to cover the signal-sensitive surface of a sensor not used for scanning to deactivate the sensor not used for scanning.