For decades, field-testing cars, trucks, and off-highway vehicles has been hampered by the bulk and relative delicacy of onboard test equipment. Companies building test equipment are always struggling with how to package and place the instruments so they are protected from rain, muck, grit, heat, and cold. They also have to ensure their equipment delivers accurate measurements and data densities without raising costs or lengthening the development process.
For off-road equipment, the usual solution is to squeeze the equipment inside an expensive custom-built box that fits in the cab or on the operator's pad. And a maze of cabling -- one per transducer -- runs from the box. Naturally, the more complex the test program, the bigger and heavier that central box must be.
In cars and light trucks, the size of the centralized test instrumentation often leads to fit and weight-distribution problems. At the extremes, the weight of the instrumentation itself affects data accuracy, especially in sports cars and race cars.
A new breed of distributed, IP65-hardened onboard data-acquisition (DAQ) systems that are immune to heat, cold, liquids, and grit let test engineers place the equipment anywhere they want, inside or outside. Users report higher testing throughput, simplified wiring and cabling, faster instrumentation setup and knockdown, and lower testing costs. And problems associated with the size of centralized onboard instrumentation have disappeared altogether. Early users also report better, more complete data because it uses 20-bit resolution and 19.2-kHz electronics.
Distributed Onboard DAQ
The new MGCsplit module puts MGCplus electronics in a small (4 X 6 X 8-in.), 5-lb, IP65 weatherproof enclosure, giving test engineers flexibility in designing and outfitting field tests. (MGCplus is the testing standard for aircraft and vehicles in Europe and is gaining favor in the U.S.) The IP65 enclosure features a mechanically rugged, shockproof case; gasproof plugs; and galvanically isolated input ports. It withstands temperatures from -22 to 58°F (30 to 70°C) and up to 2.5g of vibration and 20g of shock, enough to survive a 4-ft drop.
The electronics inside include 24-bit A/D converters on each channel for superior resolution and 19.2-kHz sampling rates for nanosecond-level simultaneous measurement. Effective resolution is 16 to 20 bits, providing 7,680,000 steps instead of the 12 bits found on the best available alternative. Precision is selectable from 0.0025 to 0.1% of full scale.
Each module is a complete, self-contained analyzer with built-in data reduction, and can send outputs to a hard disc or an external PC. Modules can be daisychained, so there's no need to connect each module to a central processor. The modules also support all mainstream transducers and testing software and work with USB, Ethernet, RS-232C, CANBus, and ProfibusDP.
Despite the higher performance capability, the cost of an MGCsplit testing system is comparable with other systems. And the cost advantage increases with the number of modules and channels in the total test package.
Other advantages include:
Solving space and weight problems. Technicians can distribute a few 5-lb rugged test modules throughout the vehicle rather than stuffing a single 75-lb console in the driver's compartment. DAQ modules also eliminate space issues and the need for heavy, protective enclosures. Minimizing the impact of a DAQ system on the vehicle being tested means the data more accurately replicates the real world. This should be of special interest to builders of race cars, sports cars, energy-efficient hybrid cars, and other ultralight vehicles.
Better correlation between field and test-stand data. Many vehicle developments rely on field and test-stand data, but developers traditionally use different DAQ systems at each venue because no single system works well in both. This has made it difficult to correlate data between the two. The MGCsplit systems are identical and fully interchangeable electronically with the familiar MGCplus system found in 70,000 modules worldwide, which can make this a problem of the past.
Analyzing transients. Older mobile test equipment built for off-road vehicle testing could not fully capture all the transient stresses and strains which are often too brief (less than 10 msec). MGCsplit has hardened, high-speed modules that bridge a long-existing gap in mobile testing equipment. In the past, fast-sampling equipment could capture transient incidents, but weren't rugged enough to survive being strapped to the outside of a military tank or pile driver. And equipment tough enough to survive didn't have the sampling speed. MCGsplit combines 19.2-kHz sampling speeds with an IP65 enclosure, giving it speed and strength.
Shorter development cycles. High-resolution measurements taken during field testing directly reduce the time and cost of developing a vehicle. That's because as the nondestructive field-test data improves, FEA becomes more effective and reliable, and the need for destructive testing declines. And even small improvements in resolution and sampling speed make a big difference in the accuracy and realism of computer models.
A workout in the fields
Farm-equipment company John Deere wanted a single standardized test platform for both field and lab tests at its proving grounds in northern France to improve data correlation between the two venues. The company was familiar with MGCplus having used it in protected enclosures. Now they wanted to use it to field test its line of attached power tools. Measured parameters would include stress, strain, acceleration, force, and temperature, usually sampled simultaneously at several different points on the tool.
The testing environment for agricultural equipment must be harsh, with muck, sand, water, stones, rough streets, and temperatures ranging from -20 to 40°C replicating the real world. Conditions on the vehicle carrying the tools are also severe with vibrations, shocks, and extreme temperatures around oil reservoirs and exhausts. Previously, John Deere engineers either built special enclosures or relied on wireless transmission between onboard sensors and a remote data-acquisition center to keep instruments out of the weather. Both were expensive and slow, which severely limited the amount of data and its quality.
The goal of their first test program with the new DAQ system was to track and correlate hydraulic pressure in the fluid-power system with the stresses, strains, displacements and accelerations on the tools. They mounted a 16-slot, 45-channel module on the tool, where it is immersed in the same harsh environment as the tool itself. There was no additional protective enclosure. Data was sent wirelessly by Ethernet to a master computer 1-km away.
On the very first test run, engineers enjoyed faster installations and removals, plus a significant reduction in equipment size and weight. The unit's sampling speed and resolution also gave them a more detailed picture of transient incidents in the 10-msec range.
A German company that builds heavy-duty construction and mining cranes tests booms to make sure they withstand the varying stresses and strains as it turns, lifts, lowers, and reaches. The tests also try to correlate stresses and strains on the boom with applied power and loads. In the past, the testing setup consisted of dozens of stress/strain transducers all over the boom, each connected to a communications processor in the cab. This made for tedious cabling and increased the risk of systematic errors due to electrical interference and noise in the long analog signal cables.
Today the company uses a battery of MGCsplit modules arrayed over the boom and hydraulic power supply. Each module on the boom serves eight strain transducers, and all modules daisychain on a single digital cable that plugs into the cab-mounted processor. With modules on the boom, analog cables leading to the strain transducers are substantially shorter, minimizing signal interference. Other modules monitor power output and conditions of the engine and fluid-power system. Typical instrumentation consists of eight voltage channels measuring power input and 16 current channels monitoring stresses and strains along the boom. The result is a real-time picture of the boom's response to fluctuating loads and movements. Crane engineers are particularly interested in transient forces stemming from complex combinations of loads, power, and motion. Many boom failures have been traced to compound transient conditions that were not well understood. Sampling rates on previous equipment were too low to capture these 10-msec transient incidents.
Testing is conducted through all seasons, so the modules are directly exposed to heat, high humidity, rain and snow. And as with the agricultural equipment, a crane's operating environment entails much shock and vibration. The DAQ systems also collects data while the crane moves over roads to the worksite and into position, which is when vibration and shock forces are most extreme.
Although the new DAQ system is still largely in the startup phase at the crane company, engineers report major savings in time for setup and knockdown of the instrumentation. They also cite better, more reliable data because the analog cables are so much shorter. Moreover, in just a few months of use, engineers have captured a fuller picture of several significant transient incidents due to simultaneous readings of all channels.
One Big Three automaker routinely puts its transmissions through their paces and carefully monitors results as part of its improvement program. Tests vary from 15 min to several days and involve anywhere from 4 to 30 measurement channels. As a minimum, every test measures output, speed, line pressure, line temperature, and coolant flow. And most tests also monitor stress and strain at various points in the transmissions.
In the past, this was all done on a single fully instrumented test stand that held all the hardware needed to run the protocol and accumulate, analyze and store data. But hooking up the transmission and then removing it from the test stand took up more time than actual testing. It could take an entire day or more to set up a 45-min run. The company considered building another test stand, but it would be prohibitively expensive. Besides, there simply was not enough room.
Instead, the company built eight small, wheeled test beds, each with its own MCGsplit DAQ package. This lets technicians do most of the instrumenting and prewiring off-line. When the test stand completes a test, the next cart is moved into place with a transmission prewired and ready. Technicians need only connect a single cable. The DAQ module on each cart not only collects good data, but also survives frequent spills of hydraulic fluid.
Engineers expect more data from the new system, and the resulting enlarged database should improve transmission design. And several trial runs have already captured transient incidents that slower instrumentation would have missed.