Abstract: [Objective] In response to the problems of traditional portable pH meters in dairy enterprises during raw milk acceptance, production process control, and finished product quality testing, such as the probe being prone to collision damage, inaccurate positioning of the folding and storage mechanism, easy loosening and deviation during use, complex operation, and difficulty in balancing portability and stability, a new type of pH meter integrating a folding storage function and a mechanical self-locking limit structure was designed. [Method] The device mainly consists of a detection host, a storage slot, a folding storage mechanism, a stirrer, a detection probe, and a limit structure. The limit structure forms a linkage system through a push rod, a rack-gear transmission component, a return spring, a screw transmission component, a sliding arm, and a fixing rod, achieving one-key unlocking, automatic reset, and reliable locking functions. [Result] Structural analysis and principle verification show that this design enables the folding storage mechanism to achieve precise positioning after deployment without significant shaking or deviation, and a compact structure after storage that effectively protects the sensing components. The overall operation is simple, the transmission is smooth, the locking is reliable, and it can significantly improve the stability and data repeatability during dairy testing, as well as extend the service life of the equipment. [Conclusion] This portable testing instrument is suitable for typical dairy industry scenarios such as laboratory analysis in dairy enterprises, rapid on-site testing in production, and outdoor sampling on pastures, providing a practical new idea for the structural optimization of portable water quality and physiochemical testing instruments in the dairy industry.

Key words: pH meter, foldable storage, self-locking limit, dairy testing, portable testing instrument