Abstract: A low-priced oil-level meter with a phase-lock loop and an MCU is described.Using ultrasound,the non-contact instrument can measure at low temperatures,has no movable parts,and has a long life span.With the PLL,the system has good performance and low cost.The MCU is used to control emission and receiving of the ultrasound,and compute the oil-level.Sources of measurement error and delays are analyzed.