Application of PICOTURN series products in turbocharger speed measurement

Preface

As an efficient, energy-saving and environmentally friendly product, turbochargers are increasingly used in modern automobiles. As a speed measuring device in the development and testing of turbochargers, the PICOTURN series products of ACAM of Germany have been widely used in many car factories at home and abroad. Compared with the previous generation of products, the latest generation of PICOTURN PT2G series products have higher integration and more flexible application.

PICOTURN speed measurement principle

PICOTURN is a device specially designed to measure the speed of the turbocharger of the engine . It consists of two main parts: the sensor and the controller. The sensor core coil is placed in an M5 threaded sleeve and installed on the compressor housing, as shown in Figure 1.

PICOTURN's measurement is based on the principle of eddy current detection. A 1MHz pulse electrical signal is added to the sensor coil , and the coil generates a changing magnetic field. When a blade approaches the sensor, the blade will have an eddy current effect in the changing magnetic field. This eddy current in turn weakens the impedance of the sensor coil. This phenomenon does not occur when the sensor is located in the gap between two blades. PICOTURN's time measurement technology can accurately measure the change in the impedance of the sensor coil. After the measurement data is calculated by DSP, the number of blades passing through the sensor per unit time is obtained, and the impeller speed is converted.

Compared to optical detection methods, PICOTURN's inductive detection method is not affected by impurities such as dust and oil. Compared to fully analog inductive blade counting systems, the fully digital PICOTURN product is more robust, easier to use and less expensive.

PICOTURN System Composition

PICOTURN's second-generation product PT2G consists of two parts: the intelligent sensor component and the control box component, as shown in Figure 2. The intelligent sensor component has an ASIC signal processing module that directly outputs a digital pulse signal whose frequency is proportional to the turbocharger speed. The control box component provides two options: displaying the speed on the panel digital tube and outputting the real-time speed through the RS232 interface.

Figure 2 Smart sensor components and control box components

Since the sensor connection cable has its own signal processing module, it can process the signal of the sensor coil on the spot and directly output a digital pulse signal, which reduces the chance of analog signals being interfered with in the long wire and ensures measurement accuracy. The wire for transmitting digital pulse signals can be very long to facilitate the installation of the control box in different locations. ACAM provides three specifications of connection cables : 3 meters, 5 meters, and 10 meters for connecting sensors and controllers.

To adapt to different turbocharger housing conditions, ACAM also provides a series of sensors with different thread sleeves, with different threads and sleeve lengths, as shown in the table in Figure 3.

PICOTURN output modes

PICOTURN can measure turbocharger speeds from 390rpm to 400,000rpm. The system provides speed output to the data logger via digital pulses, analog voltage and RS232, and can also display speed information locally in real time.

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The PT2G's intelligent sensor assembly outputs a digital pulse signal. Every time a blade passes through the sensor position, the sensor's output level jumps once, so the frequency of the output pulse is half the blade passing frequency.

Figure 3 PT2G smart sensor series

PICOTURN output modes

PICOTURN can measure turbocharger speeds from 390rpm to 400,000rpm. The system provides speed output to the data logger via digital pulses, analog voltage and RS232, and can also display speed information locally in real time.

The PT2G's intelligent sensor assembly outputs a digital pulse signal. Every time a blade passes through the sensor position, the sensor's output level jumps once, so the frequency of the output pulse is half the blade passing frequency.

The PT2G control box has two models, PT2G-BD and PT2G-BX. Both control boxes provide digital and analog output interfaces. The digital output interface provides a pulse level signal, and the turbocharger outputs a pulse for each revolution. The analog output interface provides an analog voltage signal between 0.5V and 4.5V to represent the speed from 0 to full load, with a step length of 80,000rpm/V. In addition, PT2G-BD also provides a panel LED to directly display the real-time speed; PT2G-BX provides an RS232 interface to output the speed data to other devices. There is a dial switch on the control box panel to set the number of blades of the compressor impeller so that the speed can be converted using the sensor output pulse.

Since the PT2G smart sensor outputs digital pulse signals, the speed information of the turbocharger can be obtained by counting the pulses and performing simple calculations, which greatly increases the flexibility of smart sensor applications. In addition to connecting to ACAM's own control box, the PT2G smart sensor can also be directly connected to equipment from other manufacturers. For example, if it is connected to the ES441 module of ETAS, the speed information can be sent to the Ethernet; if it is connected to the M-FRQ module of IPETRONIK, the speed information can be sent to the CAN bus .

Installation of the PICOTURN sensor

The sensor is installed on the compressor housing perpendicular to the impeller, as shown in Figure 1. The maximum distance between the sensor and the impeller is related to the shape and thickness of the blade. Generally, the maximum distance for a 0.6mm thick blade is about 1mm. For the convenience of sensor installation, an LED is provided on the PT2G control box panel to determine the distance between the sensor and the impeller during installation. By simply observing the color displayed by the LED, it can be determined whether the distance between the sensor and the impeller is within a suitable range. PICOTURN can also obtain system operation status information through the indication of the LED during measurement.

Conclusion

The PICOTURN series products have become a powerful tool for turbocharged engine testing due to their ease of use and excellent measurement performance. They have been adopted by many well-known brands such as Volkswagen, BMW, Mercedes-Benz, and Dongfeng Cummins. ACAM's general agent in China, Shiqiang Telecom, will provide comprehensive technical support for this product.