{{short description|Technique used in the development and testtesting of complex real-time embedded systems}}
'''Hardware-in-the-loop''' ('''HIL''') '''[[simulation]]''', '''HWIL''', or '''HITL''', is a technique that is used in the development and testtesting of complex real-time [[embedded systems]]. HIL simulation provides an effective testing [[platform (computing)|platform]] by adding the complexity of the plantprocess-actuator undersystem, controlknown as a [[Plant_(control_theory)|plant]], to the test platform. The complexity of the plant under control is included in testtesting and development by adding a [[Representation (mathematics)|mathematical representation]] of all related [[dynamic systems]]. These mathematical representations are referred to as the “plant"plant simulation”simulation". The embedded system to be tested interacts with this plant simulation.
==How HIL works==
A HIL simulation must include electrical emulation of sensors and actuators. These electrical emulations act as the interface between the plant simulation and the embedded system under test. The value of each electrically emulated sensor is controlled by the plant simulation and is read by the embedded system under test (feedback). Likewise, the embedded system under test implements its control [[algorithms]] by outputting actuator control signals. Changes in the control signals result in changes to variable values in the plant simulation.
For example, a HIL simulation platform for the development of [[Anti-lock brake|automotive anti-lock braking systems]] may have mathematical representations for each of the following subsystems in the plant simulation:<ref name=brake>T. Hwang, J. Rohl, K. Park, J. Hwang, K. H. Lee, K. Lee, S.-J. Lee, and Y.-J. Kim, "Development of HIL Systems for active Brake Control
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==Uses==
In many cases, the most effective way to develop an embedded system is to connect the embedded system to the real plant. In other cases, HIL simulation is more efficient. The metric of development and testtesting efficiency is typically a formula that includes the following factors:
