Optical triangulation displacement sensors detect linear displacements of objects without mechanical contact. They have simple structure, good resolution, and long operating range. However, there are several errors generated from speckle effects, environmental effects, and electronic noises, etc. To reduce errors from the electronic noises, the easiest way is to average the measurement outputs. Because the electronic noises are random in nature, their variance can be reduced with the averaging operation. However, this method is inherently time consuming process. To decrease the averaging time, several sensors or better signal processing hardwares are needed. So it increases the size of the measurement system and is not costeffective. In this paper, we propose a simple and cost-effective system structure for optical triangulation displacement sensors, which simplifies the averaging by inserting a transmission-type diffraction grating. When an incident ray enters to the diffraction grating, the grating separates the incident ray into several rays by the diffraction effect. The diffraction grating helps us to attain several signals simultaneously. Theoretical analysis is given and the feasibility of the proposed system is verified through experiments.