A method for non-destructively evaluating the concentration of impurities in an epitaxial susceptor used in the processing of a semiconductor substrate. The boom lock is arranged to lock the boom in a raised boom position. A mounting bracket connected to the drive pumps provides a fixed connection for a first end of the actuator while the opposing second end is connected by an axially moveable linkage to the pintel arms. The second drain channel chiefly discharges liquid droplets from the gas liquid separator. The switching device is coupled between the control signal generator and the driving circuit and used for alternatively controlling the on-off state of the light source by controlling the operation of the driving circuit.