Just as engineers of consumer vehicles are being asked to shorten development cycles and improve performance, reliability, and safety, so are developers of off-highway vehicles, such as construction equipment and agricultural machinery. From a practical point of view, this means running more tests and acquiring and analyzing more data in a shorter time than ever before. Good measurement data is, after all, important for optimizing designs.
Consider the following types of vehicles:
• A tractor plowing the dusty expanses of a Kansas wheat field, powering through the mud in blistering heat.
• A crane at a skyscraper building site, conveying tons of materials up several hundred meters high.
• A ship carrying needed supplies to offshore oil rigs that must get through no matter how bad the weather.
• A truck transporting material carrying tons of recently-mined ore.
Each of these scenarios share some common measurement requirements. The data-acquisition system used to test these vehicles must be rugged enough to withstand field testing, provide accurate and repeatable measurements, and be able to transmit data over the Web.
In addition, however, each scenario has its own unique requirements. That being the case, the flexibility to adapt to different measurement tasks is a very desirable feature for data-acquisition systems used to test off-highway vehicles.
To optimize prototype testing time, it is important for the measurement system to be able to withstand all kinds of harsh conditions. Rugged data-acquisition systems are needed for testing in harsh environments to reduce test times and keep the cost of repairs as low as possible.
Testing off-highway vehicles presents many challenges. Perhaps the most challenging is the operating temperature range. Some vehicles must operate at temperatures as low as -30°C, if, for example, they will be used in northern climates during the winter, while others may have to operate at temperatures up to +80°C, if they are to be used in the desert during the summer.
For performing winter tests, such as cold-cranking tests, and summer tests, such as cooling tests, a data-acquisition system is needed that can operate at very low temperatures and very high temperatures. A data-acquisition test with an extended operating temperature range doesn't need any special packaging to operate under these extreme temperature conditions.
Shock and vibration is also a consideration for testing vehicles that operate off-highway. To help ensure that a data-acquisition system will operate reliably in an environment with harsh vibration and sudden impacts, look for equipment that has been tested using test procedures found in MIL-STD-202G, “Test Method Standard: Electronic and Electrical Component Parts.” This standard specifies environmental tests used to test military electronic gear, including shock and vibration testing. Look for a MIL-STD-202G vibration rating of 10 g and a shock rating of 75 g.
Dusty and wet conditions are common when testing agricultural and mining vehicles. To ensure that test equipment will operate in conditions that are dusty or wet, look for equipment that has an IP65/67 rating. IP ratings, or ingress protection ratings, specify how well the enclosures protect against dust and water. IP65 enclosures are dust-proof and protect against water jets. IP67 enclosures are dust-proof and immersible in water up to a depth of 1 m.
IP ratings were developed by the IEC (International Electrotechnical Commission) and are mostly used in Europe, but there are NEMA equivalents. An IP65 rating corresponds to a NEMA 4 or 4X rating. An IP67 rating corresponds to a NEMA 6 or 6P rating.
Protect against unforeseen events
When operating under such extreme conditions, it's hard to anticipate all of the problems that may occur. Nothing is more aggravating than losing measurement data because of unforeseen events, such as a power failure or the data-acquisition program crashing. This is especially true for long-term tests, when the user is not always on site to monitor error-free recording of measurement data.
For situations like this, a measurement system that records data as it goes, and can pick up where it left off, is indispensable. Should there be a power outage, or some type of vehicle failure that interrupts a test, a user would at least have all the data recorded up to the interruption. The system should also automatically resume logging data after the interruption without any need for user interaction.
Another way to protect against unplanned interruptions is to check to see that the system purchased uses a stable operating system. Using a Linux operating system has in the past provided the most stability for applications such as these.
The ability to access a measurement system via the Web is very convenient when testing in harsh environments and when performing long-term tests. If a measurement system has a Web interface, it is possible to monitor the test remotely without having to monitor it on-site.
Typically a Web interface provides direct access to the measurement data–anywhere, from any Web-capable device. With the right software, it is possible to visualize test results in real time too. In addition, a Web interface can allow multiple clients to access the system and focus on the test data that is important for them.
Modular architectures for flexibility
Because off-highway vehicles come in so many different shapes and sizes, and the measurement requirements are so diverse, data-acquisition systems need to be very flexible. Systems with a distributed modular architecture make it possible to structure the system according to these varying requirements, thereby reducing overhead.
For example, when testing a very large system, such as a construction crane, the system should allow the positioning of a data-acquisition module close to where the measurements need to be made. Positioning the module close to the measurement point will minimize the effect of long sensor leads and common-mode noise, which are the leading causes of measurement errors.
Another feature that can improve the flexibility of a data-acquisition system is universal inputs. Modules with universal inputs allow users to connect different types of sensors to a data-acquisition module and record different types of parameters with a single module. This reduces the number of modules needed for a particular test.
Finally, consider how the intelligence of the software built in to the data-acquisition system can reduce the time needed for data analysis after the test. One feature to look for is intelligent processing of channel data. It is, for example, very convenient to perform real-time calculations on acquired data and then record the calculated values as an independent channel or trigger measurements using the calculated data.
Testing off-highway vehicles is definitely challenging. Modern data-acquisition systems help make it easy, offering reliable and robust measurement capability that can be used in all kinds of adverse conditions, and ultimately makes the engineer's job easier.
This article was written for SAE Off-Highway Engineering by Finn Lange, Product Manager Test & Measurement, HBM.Continue reading »