Fringe Up and Down Counter

The counter receives the quadrature signals A and B from the preamplifier (474 308). Depending on which falling edge of the TTL signal of A or B occurs first, the direction of count either up or down is defined. By exploiting the rising and falling edge of the TTL signals A and B an interpolation can be realised, resulting in a resolution enhancement of factor 2 or 4. Without interpolation one count event relates to a movement of the triple reflector of λ /2. By using the internal interpolation a movement of λ/4 or λ/8 corresponds to one count event. To calculate the movement the displayed result must be multiplied by the wavelength = 0.632 nm and divided by the interpolation factor used.
The counter is controlled by a microprocessor. The settings are done by a one button control which navigates through the available menu. Via the USB bus the measurement results can be transferred to a computer. In addition the counter can be fully controlled by a connected computer.