Monday, August 4, 2014

PicoTurn Systems Measure, Improve Turbocharger Performance

by John Monteith
Product Technical Manager, Precision Measurement Technologies

PicoTurn Systems from Precision Measurement Technologies are used to measure Turbocharger rotational speed with high accuracy. Normally this information is used to develop turbochargers and verify turbocharger performance to insure that such performance complies with the specification.

While this is the common use of the PicoTurn, there are some private and government laboratories that are also using the PicoTurn to monitor turbocharger performance as it relates to fuel consumption and emission content. These systems are being used in both engine test cell applications as well as test vehicle applications.

While the configuration of the test equipment used closely resembles that of a typical end customer installation, additional data is collected and then correlated to the parameter of interest, such as fuel consumption or the emissions coming out the exhaust pipe. With today’s turbocharger control systems it is possible to very quickly and accurately adjust the turbocharger speed and profile (in the case of variable geometry turbocharger systems). From the accurate measurement of the rotational speed of the turbocharger, you know the real-time pressure of the inlet air, allowing you to inject just the right amount of fuel to maximize fuel efficiency and to minimize emissions from the engine.

The Precision Measurement Technologies PicoTurn is a test system for measuring turbocharger rotational speed using the eddy current reduction technique. This technique directly senses each vane of the turbocharger wheel with a speed sensor that is mounted in a hole bored into the turbocharger housing as shown and diagramed below. Even at the maximum speed of 400,000 RPM, each vane is sampled multiple times as it passes the speed sensor to insure accurate detection of the vane.

Most engine manufacturers are familiar with the PicoTurn and many use it to test the performance of their turbocharger during engine testing to insure that their turbocharger is operating correctly so as not to damage the turbocharger or engine due to turbocharger malfunction.

There are two versions of the PicoTurn currently available from Precision Measurement Technologies. The BMV6 PicoTurn is currently the most popular version for engine test cell installations. This system consists of the Speed Sensor that gets threaded into the turbocharger housing and the BMV6 Signal Conditioning Module which converts the information received from the speed sensor to either an analog signal proportional to speed or a digital signal with 1 pulse per revolution. This is the configuration that is being used by the laboratories correlating turbocharger performance to fuel consumption and emissions.

While the BMV6 PicoTurn is certainly popular, the PT2G PicoTurn offers much better performance, longer extension cable lengths and can be used with or without the PT2G Signal Conditioning Module. The enhanced features actually make the PT2G PicoTurn more suited to these laboratory applications.

The PT2G PicoTurn features make this system ideal for test vehicle applications because the sensor can be located up to 40 feet from the test equipment and the Speed Sensor can directly feed into engine controllers and test equipment with frequency counter capability. These same enhanced features also make the PT2G ideal for test cells. If a signal conditioning module is desired to get an analog output, the signal conditioning module can be located in the same area as the other test equipment by using the ACAM Sensor Extension Cables up to 40 feet in length. The speed sensors themselves present one pulse per vane instead of one pulse per revolution offering the highest resolution possible. With digital test equipment reading the sensor directly, you get a very high resolution picture of what the turbocharger is doing at any given instant.

The Speed Sensors and the Extension Cables have AMP Super Seal connectors that make them ideal for under hood applications and test cells where fluids can leak onto the cables.

While PicoTurn is used in many everyday applications, there are laboratories that are using PicoTurn for many unique applications. We will continue to feature articles on these unique applications to keep you up to date with how PicoTurn equipment is being used.

John Monteith, Product Technical Manager for Precision Measurement Technologies, has 39 years of experience in new product design, project team management, semiconductor design, and applications engineering.  John has been with PMT since its inception and for the last five and a half years has been focused on supporting a wide range of projects utilizing time-to-digital technology in high precision measurement applications.