Signal Paths

In Hardware-in-the-Loop (HIL) systems, a signal path refers to the complete route a signal takes — either from the Device Under Test (DUT) to the acquisition hardware, or from a signal generation source back to the DUT. This path includes both physical connections and logical routing, and is defined by the hardware components involved and the I/O capabilities required.

Each signal path is built around a specific type of I/O operation and typically starts at one of the following points:

Discrete I/O

These are basic electrical signals used for simulating or measuring simple states or values:

• Analog I/O
• Digital I/O
• PWM (Pulse Width Modulation)
• Resistor Simulation

Communication Buses

Used for simulating or interfacing with automotive and industrial communication protocols:

• CAN, LIN, FlexRay
• Automotive Ethernet, RS485, EtherCAT, Standard Ethernet

Instrumentation I/O

Used for high-precision signal generation and measurement:

• Digital Multimeters (DMMs)
• Oscilloscopes
• Function Generators
• Network Analyzers
• Signal Generators

Each I/O type is characterized by a set of technical parameters, including:

• Channel count
• Voltage/current range
• Impedance
• Bandwidth
• Sample rate
• Resolution
• Accuracy
• Isolation

In NI HIL systems, these signal paths and specifications are typically implemented using PXI modules, which provide modular, high-performance I/O tailored to the needs of automotive and industrial test environments.