def read_probes(self, key):
        """
        requestes value from the instrument and returns it
        Args:
            key: name of requested value

        Returns: reads values from instrument

        """
        assert key in list(self._PROBES.keys())

        if key == 'output':
            value = self._output

        return value
requestes value from the instrument and returns it
        Args:
            key: name of requested value

        Returns: reads values from instrument