Model 431 X-Y Optical Position Indicator

When interfaced with tetra-lateral devices, pin-cushion photodiodes, or quadrant detectors, the Model 431 determines the X and Y location of the centroid of a light spot on the detector (the Model 431 is incompatible with duo-lateral detectors).

The Model 431 uses a network of analog amplifiers and dividers. The first amplifier stages operate in the transimpedance mode, boosting the photodetector current and converting it to a voltage. The secondary stages add and subtract the signals from each of the front-end amplifiers. A divider network divides the difference by the sum. And a final buffer amplifier drives the digital display and analog output.

The front-end amplifier gain adjusts over 4-1/3 decades. This lets you optimize the signal-to-noise ratio for the incident light level. The sum and difference stage gain adjustments establish the detector’s sensitivity light spot movement. With the front-panel quadrant/continuous select switch, you select the appropriate amplifier sequence as a function of the detector type in use.

Five BNC connectors on the rear panel present the X position, Y position, X sum,Y sum, and total sum signals. The position signals are scaled from 0 to ±2VDC (to coincide with the 3½ digit display), and sum signals range from 0 to +10VDC. A printed circuit board edge connector also provides each of the four preamplifier outputs, the X and Y difference outputs, and test voltages from the power supply (+7V, -7V, +15V, -15V).