Our PT-Series optical interference testing rig for applanation tonometers consists of an automated laser-based testing device equipped with a serial interface for coupling to a PC, plus signal-processing software running on standard PCs/notebook computers. Its flexibility of configuration allows its use with various types of tonometers. The buckling force set on the tonometer to be tested is automatically recorded over its full travel. Detecting the limits of the tonometer's travel allows to output both its buckling-force characteristic curve over its full travel and the buckling force at the midpoint of its travel, as stipulated by testing regulations. The force sensor employed is an optical-interferometric device with a measurement range of 100 mN and a resolution of 0.01 mN. 
To test a tonometer, the tonometer is driven up against this force sensor by an electromechanical drive,  where the measured buckling-force characteristic curve is employed internally for controlling the motions of the drive and detecting the limits of the tonometer's travel. The measured value

of the buckling force at the midpoint of the travel is then compared with the prescribed tolerance range and displayed either in green, indicating that it falls within that range, or in red, indicating that it falls outside that range. A complete series of measurements, including outputting a test report to a file, takes less than five minutes, thanks to the fully automated test procedures of the rig. The facilities provided for calibrating its optical-interference force sensor using standard weights allow to trace its calibration back to national reference standards.