The grid type displacement transducer includes the motion ruler and fixed ruler. The characteristics are that the numbers of the grid lines of the motion and the fixed rulers are designed asunequal. The equivalent grid line number is increased greatly by difference of their grid line numbers. The equivalent grid line number lambda satisfies the relational expression: lambda=NN'/n, where N as the grid line number of the motion ruler, N' as the number of the fixed ruler, N' larder than N and n as greatst common divisor between N and N'. Elimination of each periodic error outside the times of Ni (I=1,2,...) I realized based on use of the relation between the differences of the grid line numbers of the motion ruler and the fixed ruler. Thus, the precision is improved greatly. |