Sensor Technology drives accuracy of Diesel Engine Testing.

Today's diesel engines must meet the stringent environmental requirements of legislators and regulators, while satisfying the performance demands of OEMs and end-users. To guarantee top engine performance under a full range of operating conditions and to ensure overall engine reliability and conformance, a full test facility is required.

Power Test, Inc., of Menomonee Falls, Wis., provides a complete engine testing solution for commercial, government, and military applications. Power Test manufactures dynamometers for the entire diesel industry, including engine and chassis dynamometers and compatible data acquisition systems. A dynamometer applies a load to a running engine, allowing engineers to determine the engine's torque, horsepower, safety, and potential trouble spots.

Dynamometer Technology
In the Power Test dynamometer, water flow, proportional to the desired applied load, creates resistance to the engine. A controlled water flow through the inlet manifold is directed at the center of the rotor in each absorption section. This water is then expelled to the outer dynamometer body by centrifugal force. As it is directed outward, the water is accelerated into pockets on the stationary stator plates where it is decelerated. The continual acceleration and deceleration causes the dynamometer to absorb the power produced by the engine. Through this transfer of energy, the water is heated and discharged.

An integral component of a Power Test dynamometer is its data acquisition system. The system is comprised of two units, called Commander and Workstation, connected by an Ethernet cable. Commander, a desktop computer operated by Windowsä-based software, issues commands to Workstation, a touch-screen-operated unit housed in a rugged industrial enclosure. Workstation operates the precision load and throttle control systems, collects the data, and sends it to Commander to be processed, stored, and analyzed.

Workstation's success, and therefore the data acquisition system's accuracy, depends on its ability to correctly measure data in the dynamometer tests. Central to these measurements is the precision of its pressure sensors, which measure airflow in the intake manifold, oil pressure, and other fluid pressures. According to Power Test Project Engineer Allen Bergst, "The operator is interested in different pressures of fluids. So having the capability of bringing in pressures while you are running the engine is very important." For this essential task, Power Test uses pressure transducers from Setra Systems, Inc., of Boxborough, Mass.

Sensor Technology
Setra Systems is a designer, developer, and manufacturer of high accuracy electronic pressure sensors and other electronic measurement instruments. Setra's products are used by process and manufacturing industries, federal agencies, and research laboratories. Setra Systems derives its accuracy from its patented capacitive transducer design, coupled with its proprietary circuitry, which produces a strong signal that generates an accurate output.

In a typical Setra configuration, a compact housing contains two closely-spaced, parallel, electrically-isolated metallic surfaces, one of which is a diaphragm capable of slight flexing under applied pressure. These firmly secured surfaces are mounted so that a minute change in applied pressure alters the gap between them, creating a variable capacitor. The resulting change in capacitance is detected and converted to a proportional high-level analog signal.

Sensors Meet Manufacturer's Demands
Power Test uses Setra's Model 209 Industrial/OEM Pressure Transducer because of its ability to measure accurately in rugged conditions. The Model 209 withstands mechanical shock and vibration, thermal shock, corrosion, and other extremes found in harsh testing environments of dynamometers.

Setra's Model 209 Pressure Transducers are custom-configured for Power Test's water brake dynamometers. The pressure transducers are mounted as shown in the "Workstation," the data acquisition system of the dynamometer

Bergst says Setra's sensors are ideal because of their flexibility. "We needed versatility in the pressure ranges that we were sensing," he explains. Setra customizes the Model 209 to Power Test's specifications because the engine tester often requires uncommon ranges. The Model 209 has a standard range of 0-50 PSI or 0-100 PSI for low pressure measurement, but Power Test required sensors with ranges of ±15 PSI, 0-2 PSI, 0-20 PSI, and 5-100 PSI. Setra Systems Product Manager, Jean Collins, says customization of the Model 209 is well-within Setra's capabilities. "The transducers' capacitive design allows for simple modifications to meet our customers' wide range of needs, so we were more than equipped to help Power Test with its request for uncommon pressure range measurement."

The dependability of Setra's design has led to the development of pressure transducers that fit the unique requirements of Power Test's engineers. "Setra has been very good to us as far as its ability to produce a specialty range sensor to meet our specifications with fast delivery time," Bergst states. He adds that "Setra was the only company we found that had a wide range of pressures all within the same compact package." This enabled Power Test to seek only one manufacturer for all its sensors.

Power Test also benefits from the output design of Setra's transducers. "Setra's pressure transducer has an amplified output as opposed to a millivolt output, so we don't have to amplify the signal output of the transducer," explains Bergst. This means the data collected cannot be distorted due to amplification, resulting in more accurate measurements and ultimately a more efficient engine.

In addition to the Model 209, Power Test uses Setra's Model 276 Barometric Pressure Transducer. Engine performance is dictated by a variety of conditions, including atmospheric pressure, so engineers must compensate for varying barometric pressures. For example, engines tuned at sea level will likely have decreased performance at higher elevations. "Measuring atmospheric pressure is necessary to correct the amount of horsepower generated by the engine," says Bergst.

To ensure engine quality, performance, torque, and environmentally correct emissions, engine testers must run the engine under road conditions. Power Test's dynamometers allow engineers to fully test engines, while the data acquisitions system gathers and analyzes the data associated with each test. Essential to the success of the entire system, and thus the proper analysis of the diesel engine, is the accuracy of the dynamometer's pressure transducers. Power Test entrusts its dynamometer measurements to Setra Systems' pressure transducers. Setra's capacitive technology has yielded accurate results over time, and Setra has economically customized its product without sacrificing precision.


For more information contact:-

Diane Shaughnessy, Setra Systems, Inc.

July 2002

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