Due to the high level of sophistication and complexity of today's Electronic Control Units (ECU) devices, special test methods are required. The idea of testing for system failures is not new, it is an important aspect of ECU validation and involves the introduction of electrical faults into a system (fault insertion testing). The test process typically duplicates various conditions which could occur because of corrosion, short/open circuits and other electrical failure inherited through age, damage or even faulty installation.
Typically, ECUs under development are exercised by a test system that simulates the device that the unit will control – this is sometimes called a Hardware-in-the-Loop (HIL) simulation. Stimulus instrumentation that simulates engine behaviour, for example, is connected and controlled either by manual operation or by computer with measurement instrumentation used to capture analogue and digital responses from the ECU. When it is necessary to inject faults, traditionally a patch panel, such as that shown in Figure 1, has often been used.
The various cables shown are used to connect any input/output (I/O) line of an ECU to stimulus or measurement instrumentation. The I/O lines may be manually disconnected to simulate an open-circuit or tied together to simulate short-circuits and the results measured. This type of solution has many inherent disadvantages, not least being size. There are also many hidden costs such as on-going maintenance issues, the need for significant knowledge on the part of the operator, potential human error and the cost of labour required to execute the test and record results.
Another major disadvantage of any manual method is the lack of repeatability. The ability to quickly reproduce a failed test condition is essential in a test system, either to aid development or to take corrective action. Being able to precisely reproduce the test procedure quickly is a major advantage in any upgrade or verification program.
The ability to gain software control of both instrument routing and the insertion of real-time electrical faults enhances
both the testing process and the recording of the outcome. However, although a standard crosspoint matrix with an adequate
specification is capable of handling the instrument routing to the device under test, the insertion of faults requires
a specific switching architecture.
Modular Fault Insertion Solutions
Pickering offers a comprehensive range of PXI Fault Insertion Unit (FIU) switch products . These scalable solutions may be used to switch signals between simulations and real-life devices in a multitude of HIL simulation and test systems. The FIUs can help to considerably simplify and accelerate the testing, diagnosis and integration work in HIL applications. The following are some of the most common fault insertion architectures (based on examples of our FIUs):
Single Fault Bus Architecture
Figure 2 - Single Fault Bus Architecture
This architecture shown in Figure 2 is used on our fault insertion modules (40-195 and 40-196) . In these two cases the input connections are grouped in pairs and then multiple pairs have a connection allowed to a single fault bus. Using this architecture a variety of faults can be simulated in the following ways:
- Either input connection disconnected from its output
- Input connection pair shorted together
- Either input connected to the fault bus
The fault bus could be a power supply, system ground or some other connection in the system. If more than one fault bus condition is required to be simulated then additional (external) switching has to be used to expand the possibilities, or a different architecture used.
Multiple Fault Bus Architecture
This architecture, shown in Figure 3 below, provides greater flexibility and is used in a variety of our FIU modules . Using this architecture a variety of faults can be simulated:
- Any input disconnected from its output
- Any output connected to one of two fault buses
Any output shorted to any other output if the fault bus is disconnected
In the architecture used by our 40-190 series fault insertion modules , the fault bus can be disconnected or can be connected to any of four fault conditions, this allows the bus to connect to ground, a power supply or some other condition. As the connections are made with SPST switches setting them all open will allow the fault bus to be disconnected and permit a short between two signals to be created by closing two relays.
Figure 3 - Multiple Fault Bus Architecture
Fault Insertion Matrix
Our fault insertion matrices (40-592 and 40-595) provide a more complex architecture that can be used in a variety of ways for complex fault insertion tests.
The common way of using the fault insertion matrix (shown in Figure 4) is for the connection between the controller and the sensor to be on the X axis. A connection from an input (for example) is made to X1.1 and its output from X1.2. In this example the default condition is for a connection to be made by the normally closed relay. Much more complex faults can be introduced:
- Open circuit between input and output
- Fault on the output to X1.2, which could be component inserted by a patch panel arrangement.Connection of any input to one of four fault buses (Y1 to Y4)
- Connection of any output to one of four fault buses (Y5 to Y8)
- Short circuits between wires by using an unused X column to provide the short on an unused Y row
Addition of other shunt components between wires using Y axis.
The variety of fault types that is simulated is large and the third connection on each X axis adds a great deal more flexibility.
Figure 4 - Fault Insertion Matrix
Our FIUs are available in a wide range of channel counts and fault bus configurations with current handling capabilities from 1Amp to 30Amp.
The image to the right shows a high channel count automotive ECU validation system based on our PXI based fault insertion units (photo courtesy of Clemessy) and below are two examples of our PXI fault insertion modules.