Retrieve the detector file for given detector id

        If t0set is given, append the calibration data.

def detx(self, det_id, t0set=None, calibration=None):
        """Retrieve the detector file for given detector id

        If t0set is given, append the calibration data.
        """
        url = 'detx/{0}?'.format(det_id)    # '?' since it's ignored if no args
        if t0set is not None:
            url += '&t0set=' + t0set
        if calibration is not None:
            url += '&calibrid=' + calibration

        detx = self._get_content(url)
        return detx