An arrangement for measuring process parameters within a processing chamber is provided. The arrangement includes a probe arrangement disposed in an opening of an upper electrode. Probe arrangement includes a probe head, which includes a head portion and a flange portion. The arrangement also includes an o-ring disposed between the upper electrode and the flange portion. The arrangement further includes a spacer made of an electrically insulative material positioned between the head portion and the opening of the upper electrode to prevent the probe arrangement from touching the upper electrode. The spacer includes a disk portion configured for supporting an underside of the flange portion. The spacer also includes a hollow cylindrical portion configured to encircle the head portion. The spacer forms a right-angled path between the o-ring and an opening to the processing chamber to prevent direct line-of-sight path between the o-ring and the opening to the processing chamber.