Multi-channel telemetry solutions

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1 Multi-channel telemetry solutions CAEMAX and imc covering the complete scope imc Partner Newsletter / September 2015 Fig. 1: Schematic of a Dx telemetry system with 4 synchronized transmitter modules

Introduction Testing in automotive engineering has its focus shifting from simple one-dimensional tasks to increasingly complex subsystems that could typically incorporate multiple rotating parts.

2 Introduction Testing in automotive engineering has its focus shifting from simple one-dimensional tasks to increasingly complex subsystems that could typically incorporate multiple rotating parts. This trend towards more holistic approaches in examining vehicle components poses special challenges in particular to the involved telemetric signal transmission systems. This domain is one of the core areas of expertise for Munich based company CAEMAX which has developed a number of innovative solutions in this field. Taking a look back In the past, things weren t exactly easier, but less complex: Endurance tests would systematically investigate the loads and stresses that individual components are exposed to during operation. For a rotating component such as a shaft, an axle or a wheel, the sensor lead would be replaced by a telemetric system. Such single channel telemetric systems measure and capture the signal directly on the moving component and transmit the signal to the associated receiver station via radio. Present challenges For today s automotive R&D issues, measurement equipment of that type is proving more and more inadequate: For instance, if the efficiency of a complex drive train having multiple driven axes is to be measured dynamically, it is necessary to capture data from multiple components simultaneously. In classical, analog telemetry solutions, this requires the use of multiple individual systems operating in parallel and on separate radio frequencies. These separate telemetric systems and channels need to be integrated by an extra subsequent system. Fig. 2: Oberaigner 6x6 on the basis of a Mercedes-Benz Sprinter The consequences are familiar: true simultaneous sampling and thus precise time resolution of events cannot be achieved by this means. Making any changes to the configuration is tedious, and prone to error, since each system needs to be reconfigured separately. If in addition, installation constraints require the instrumentation to use different systems with differing specs and properties, measured data are no longer directly comparable. 2

3 In most analog telemetry systems still prevailing today, the measurement signal is modulated onto a high-frequency carrier. Along the path from the transmitter to the receiver, this signal is exposed to environments of potentially disturbing electromagnetic fields: electric motors and other electrical actuators can seriously degrade the signal and compromise its integrity. If the test engineer fails to detect and manually correct those errors, such corrupted data can easily challenge the subsequent analysis and simulations altogether and consequently endanger the correct evaluation of the tested component. The innovative Dx telemetry measurement system With its product Dx telemetry, the company CAEMAX is pursuing an innovative concept for simultaneous capture of data from multiple rotating components. Up to 4 transmitter modules (SCTs) can be operated by a control- and receiving unit (RCI). While the 4 modules may be located on different rotating components, they are controlled and synchronized by the central RCI (see Fig. 1). This guarantees highly simultaneous sampling of all distributed measurement signals. Setup of sampling rates and initiating zero balancing is also controlled centrally, ensuring consistent conditions on all measurement locations. The receiver unit (see Fig. 3) synchronizes and controls the individual transmitter units and compiles their readings into a single data stream. No further hardware is needed for integration of the data. Fig. 3: Receiver unit (RCI) of the Dx telemetry system Serial transmission of the measurement data allows multiple modules to transmit their data via the same radio frequency without collisions or interference. Additional systems within the same environment can operate on a number of additional radio frequencies available. This facilitates tests of multiple vehicles simultaneously without any interference. In environments with high EM exposure from electric-motors or other electrical equipment, a robust telemetric transmission path is the key to reliable measurements. For this reason, the Dx digitizes the analog sensor signals as early as possible, directly in the transmitter unit. Such digital data stream, to be decoded by the receiver is by far more robust against interference than any analog radio modulation schemes. This digital concept allows additional provisions for automatic error detection and correction by means of CRC checksums. This way any corrupted samples can be either restored or discarded reliably, in order to provide only correct and consistent measurement data. The control unit s two antennas, working in parallel in diversity mode, further improve immunity and reliability. The redundant double transmission paths can easily tolerate temporary degrada- 3

4 tion or poor reception on one antenna by seamlessly switching to the other one. Instead of a large selection of specialized modules, CAEMAX relies on a transparent one fits all design concept: one single and uniform all-purpose transmitter unit can be deployed for a variety of sensor types (strain gauge, thermocouples, accelerometers ) and channel counts. The particular configuration is set by the Dx receiving unit s firmware. This concept also allows for easy upgrade of the Dx functionality via firmware updates. The Dx system s high degree of flexibility is also reflected by the transmitter modules power supply options. Depending on the requirements of the current test situation, the user can choose between inductive power transmission or direct DC supply. Additionally, the temperature at the measurement location and the supply voltage can be measured and transmitted for diagnosis. All signals are live displayed on an OLED-Display in physical units. Typical use case: the Oberaigner company At the company Oberaigner Powertrain, the Dx telemetry system has had the opportunity to prove its worth in the survey of complex powertrain systems. Oberaigner is a leading expert in the R&D of automotive system components. For over 20 years, Oberaigner has been developing and providing major components for all-wheel versions of transporters by notable manufacturers such as Daimler, Renault and Opel. Its product portfolio includes complete drive shafts, gears, and differential locks, and even complete vehicles. Additionally, Oberaigner invests heavily in R&D of new drive technologies. The process of evaluating new developments such as a new front axle, for instance, requires exhaustive testing and experimenting. Load and stress models obtained in simulations have to be verified and refined by tests under real world physical conditions such as road tests on proving grounds. Torque measurement at the drive shaft One of the key tasks in a test drive is to monitor the torque at the drive shafts. When converting rear wheel drive transporters to all-wheel drive, a transfer case is coupled to the transmission, which allows switching between gear reduction and differential lock. Both the rear and front axles are driven from the transfer case via drive shafts. In the Oberaigner 6x6 (see Fig. 2), there is a transit gear box in the first rear axle, which splits the torque between the two rear axles, while the drive torque is delivered via a short cardan shaft. Fig. 4: Dx transmitter module with inductive (wireless) power supply installed on an Oberaigner driveshaft 4

The distribution of torque between the two driven axles is to be measured precisely for various manoeuvers, in experiments that rely on Dx telemetry.

These units are governed by a Dx receiving unit, where data from all transmitters are centrally collected.

5 The distribution of torque between the two driven axles is to be measured precisely for various manoeuvers, in experiments that rely on Dx telemetry. For this purpose, Dx transmitter units are placed on each of the three drive shafts, where they measure the torque (see Fig. 5). These units are governed by a Dx receiving unit, where data from all transmitters are centrally collected. In order to allow quick and convenient installation, the Dx transmitters are built into a robust housing which already contains the secondary coil for the wireless inductive power supply. Once the strain gauge foils for torque sensing are applied, the system is ready to operate almost immediately. For rugged use in the field, this sealed housing provides reliable protection for the sensitive strain gauge equipment against humidity and stone impact, and can be reused many times. Due to the installation situation behind the distribution gearing, inductive power supply to the transmitters was not applicable. For this reason, a rechargeable battery was installed inside of this housing (see Fig. 4). Here, too, the same standard transmission electronics could be used, since the transmitter modules support both DC- and AC supply power. Fig. 5: Dx transmitter module (SCT) with built-in rechargeable The integrated turnkey solution For a comprehensive assessment of the all-wheel drive vehicles properties, along with the telemetrically transmitted torque signals from the strain gauges, there are additional variables to be measured: temperatures, acceleration, forces, as well as control unit information carried on the CAN-Bus, and GPS data. All measurement signals must be captured in synchronization in order to be useful for subsequent analyses and calculations. To meet these requirements, Oberaigner relies on the modular measurement system imc CRONOSflex (see. Fig. 6), which is able to directly integrate the Dx telemetry system. The system can flexibly be arranged from a selection of different modules, suited to adapt to the widest variety Fig. 6: imc CRONOSflex modular measurement system of sensors and can capture all resulting channels of multi-domain signals in full synchronization. One of its key features which is especially helpful in road testing is the availability of online calculations performed onboard the data acquisition system. Already during the test drive, the test engineer can evaluate live calculated variables of interest derived from the raw signals such as torque, power, energy, spectrums etc., or 5

6 perform an online classification. The results obtained from the road testing are subsequently reflected in the simulation in order to reconcile the model calculations with real world observation. Additionally, the data acquired can serve as route patterns for test cell experiments. They can for example be used to generate realistic standard load profiles for endurance tests on stationary dynos. Conclusion Whether the task is just single-channel signal acquisition, or a complex, multi-component system: today s telemetry systems are facing ever more versatile and demanding requirements. The CAEMAX Dx telemetry system meets these challenges with universally deployable transmitter modules which allow measurements with various channel counts and sensor types. The system s synchronized operation across multiple transmitters governed by a centralized receiving unit is a novelty. It facilitates highly simultaneous measurements and data acquisition on multiple rotating components. At the same time, intelligent digital radio transmission technology ensures reliable operation and data transfer even in highly demanding and electrically polluted environments. By means of a web-based setup interface, the Dx can be configured in a matter of minutes and its measurement modes can flexibly be adapted to whatever the testing applications demands. In conjunction with the modular imc measurement system, a complete turnkey solution is at the user s disposal, in which multi-domain measurements of all sensors and signals in vehicles, machinery and production facilities is performed in synchronization, and a full perspective view of the test object is presented. About the manufacturers CAEMAX Technologie GmbH, Munich CAEMAX Technologie GmbH, headquartered in Munich, is a manufacturer of specialized systems for the R&D departments of the automotive and mechanical engineering industries. The core of its product spectrum is its proprietary automotive sensors and telemetry systems. The focus is on the best possible and most comprehensive solution for the customer s specific measurement challenges. This includes providing software and customized engineering services. imc Meßsysteme GmbH, Berlin For 25 years, the company imc Meßsysteme GmbH has been manufacturing hardware and software solutions in the field of physical measurements for customers around the world. Whether on board vehicles, in test rigs, or monitoring production facility equipment, data acquisition with imc s systems has proven effective, user-friendly and economical. For the fields of R&D, product testing, and system commissioning, imc offers both turnkey measurement system solutions and also a wide range of standard instruments and software product lines. Editors: Charlotte Pix, CAEMAX Technologie GmbH, Nils Becker, imc Test & Measurement GmbH 6

Precise, simultaneous data acquisition on rotating components Dx telemetry: from single channels to complex multi-component systems

Precise, simultaneous data acquisition on rotating components Dx telemetry: from single channels to complex multi-component systems Application: Dx telemetry used to test the complex drive train in this