Electrical lockout photoplethysmographic measurement system

Abstract

A photoplethysmographic measurement system includes an electrical lockout to effectively prevent users, such as patients and medical personnel, from being exposed to high levels of light energy illuminating from light emitters ( ) housed within a main instrument ( ) when a probe ( ) becomes detached from the system during use. The probe ( ) is provided with a resistor having a range of resistor values. In use, the electrical lockout frequently or continuously interrogates the probe connection and determines whether the detected value of the resistor falls within predetermined allowable levels. If the probe ( ) inadvertently becomes disconnected from the main instrument, the value of the resistor will fall outside of the predetermined allowable levels indicative of an incompatible probe, an improper coupling of the probe, or a complete detachment of the probe. In this case, lockout switch ( ) is employed to inhibit activation of the light emitters ( ). When a proper connection is re-established, the electrical lockout will recognize the value of the detected resistor and send a signal to close the lockout switch ( ), allowing current to pass and re-energize the light sources. Alternatively or in addition, the electrical lockout may include a circuit or a mechanism for detecting a presence of a light sensor ( ) in the probe by checking for the appropriate forward voltage drop on the conductors ( ) connected to the light sensor.