Digital-analog interface for insertion between a digital control signal transmitter and a controlled moving element

In a closed servo-loop system for insertion between

• on the one part a control circuit of a moving element, such as the servo-valve of an electrohydraulic servocontrol, whose position X is to be controlled by analog electrical signals, and
• on the other part a transmitter of signals for controlling the position X to be imparted to the moving element, said transmitter providing digital electrical control signals,
• said closed servo-loop system including
• an inductive linear position detector having a movable plunger connected to said moving element and a differential transformer for detecting the position X of said moving element, said detector having a single primary winding and two secondary windings, said two secondary windings generating voltages V.sub.1 and V.sub.2 varying with the position of the movable plunger, the difference of voltages V.sub.1 and V.sub.2 being proportional to the position X of the moving element and the sum of said voltages V.sub.1 and V.sub.2 being proportional to a constant A, and
• a digital-analog interface unit including
• first summing means connected to receive said voltages V.sub.1 and V.sub.2 and for adding voltages V.sub.1 and V.sub.2 and for forming an output signal,
• second summing means connected to receive said voltages V.sub.1 and V.sub.2 and for subtracting voltage V.sub.1 from voltage V.sub.2 and for forming an output signal,
• first resistance means having an adjustable value Ri and connected to receive said output signal of said first summing means,
• second resistance means having a fixed value R and connected to receive said output signal of said second summing means,
• means for adjusting the value of said first resistance means to Ri=R.multidot.A/X,
• summing circuit means having an input connected to said first and second resistance means, and
• a synchronous demodulator having a signal input connected to the output of said summing circuit means and a synchronization input connected to receive said output signal of said first summing means, said demodulator having an output for transmitting an output signal of said interface unit to the control circuit.