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Wiring Considerations for Modern Hardware-In-The-Loop Systems

Table of Contents

  1. Challenges of Traditional Wiring Systems
  2. Implementing a Flexible and Maintainable Wiring Strategy
  3. Conclusion

In many safety-critical industries like automotive and aerospace where the cost of failure is extremely high, hardware-in-the-loop (HIL) testing is a best practice for finding software defects and bugs as early as possible. In this testing methodology, real-world scenarios are recreated through various electrical signals and network messages that are used to simulate the world around an electronic controller and make that device believe it is actually deployed into a vehicle like a car or plane. One critical factor that must be considered in order to have accurate testing results is the signal connectivity of the test system. And, unfortunately, due to the rapid rise in electronic complexity of the devices, wiring and connecting the system to the device under test can be quite extensive and cumbersome. But with the right connectivity and signal path routing, the HIL test system can be architected in a way that reduces the amount of point-to-point wiring and therefore makes it more maintainable and flexible.

Figure 1. The software complexity of cars is growing at an increasing pace and is only continuing to accelerate

1. Challenges of Traditional Wiring Systems

Although there is a trend towards the use of communication networks to reduce the amount of wiring in a car or plane, there is still a need for large cable harnesses. For example, a plane may require a lot of wiring, even for an HIL test system, because there can be triple redundancy built in to the electronics.

The impact of faulty or unreliable connectivity can weigh heavily on the testing process resulting in engineers spending a lot of time maintaining and troubleshooting the test system while losing valuable test time which can ultimately result in the loss of confidence of the tester. Point to point wiring, although very flexible, is a continuous concern for test mangers. Hardware in the loop systems can easily have over a 1000 signals with these requiring on average 5 terminations per signal, this results in 5000 termination points with potential to be wired incorrectly requiring rework or failing in the field due to routine use and system modification.

Figure 2. Signal routing for a typical HIL system.

2. Implementing a Flexible and Maintainable Wiring Strategy

For HIL applications, National Instruments recommends using connectors from companies that have a strong reputation in the Test and Measurement industry. For example, the i2 Micro iCon connector from Virginia Panel Corporation (VPC) meets the needs of many HIL systems by offering high cycle-life, high density, high current, and the ability to have both a panel mount and circuit card mount options.

Figure 3. VPC i2 Micro iCon PCB Mount

The circuit card mount option using the twin-female QuadraPaddle contact is easy to assemble and allows the system building to reduce the amount of point to point wiring by accumulating and routing signals on printed circuit card. Building a system in this way hard codes the signal path into groups of signals so instead of running a cable for a single signal you can now use a cable with a collection of signals coded to a specific receptacle on either end to avoid missing wiring. If the signal path needs to be adjusted, only the circuit card would need to be modified, reprinted and inserted into the system.

Low insertion force allows the high density harness to be quickly and easily removed and a different DUT to be connected to the simulator. The connector's keying ability means that the harness will always be coupled correctly the first time. Due to the complexity of the DUTs, the ability to have the right keyed connectors on the harnesses will ensure proper connectivity so the signal routing is correct for each DUT.

VPC connectivity in combination with NI's PXI platform allows system builders to create modular HIL systems by handling the IO in predefined "chunks". Systems designed like this are highly modular and easy to expand to include additional IO or modify the signal flow to include fault insertion at a later point.

3. Conclusion

Overall, system connectivity and signal path flow can be an important factor in designing HIL test systems that are flexible and easily maintainable. With the right strategies using modular and flexible test equipment like the NI PXI HIL test platform combined with the right connectivity options like VPC's iSeries family, you can design test systems that are made to be easily maintainable, flexible enough to adapt to multiple DUTs, and ensure the right signal paths to give more accurate test results.