Internet of things (IoT) is developed to sense and control physical environment. Its control of physical environment is based on the sensed information and the users' requirements. Therefore, sense-execute model (SEM) is the core module in software architecture of IoT. In order to finally achieve the goal of developing IoT software guided by software architecture, this paper is dedicated to refining SEM in a physical-model driven software architecture (PMDA). The refined sense-execute model is called R-SEM. R-SEM divides the component of SEM into subcomponents according to the features of IoT and the procedures of physical application. Each subcomponent illustrates the functions of a port of a component of SEM, and is expressed by the communication sequential process (CSP). Synchronization between ports of component and subcomponent is illustrated by the pipeline operation of CSP. The interaction between subcomponents is illustrated by CSP as well. R-SEM is verified by the process analysis toolkit (PAT). The result of the verification validates that R-SEM keeps the properties of SEM, namely deadlock-free, nonterminating and divergence-free, which is necessary to guarantee valid interconnections among physical applications. Since R-SEM not only refines components in SEM but also keeps the valid properties of SEM, PMDA can be finally used for guiding software development in IoT.