Road Load Data Logger and Signal Conditioning for MTS Test Bench

The same Dewesoft R8rt data acquisition system can be used as:

• A high-channel-count test bench data acquisition system

• Real-time signal processing for road load analysis feedback (over EtherCAT) 

• It can also function as a compact-size high-performance mobile data logger for in-vehicle data acquisition use.

The new FlexTest digital controller software features support for EtherCAT communication. This offers a more cost-effective, ethernet-based digital link to third-party sources of data. The added EtherCAT support enables FlexTest users to establish digital communication with data acquisition systems.

SIRIUS DAQ systems have already been used in many signal conditioning applications for test bench instrumentation. But only as a preamplifier with analog output of +-10 V which was used as an input to the controller analog input stage.

The secondary input stage can now be completely removed thanks to the direct conversion of analog data to the EtherCAT bus inside the SIRIUS data acquisition systems. This significantly improves the user experience since there is no need for additional controller analog inputs. 

It is a 2-in-1 instrument. The R8rt DAQ system can easily be taken out of the cabinet and also used as a high-channel-count and high-speed in-vehicle data logger. 

This also vastly reduces the cost of required instrumentation and removes kilometers of cabling which indirectly also significantly simplifies the configuration setup.

Furthermore, the hardware setup is much simpler due to reduced cabling. Only a single cable is required from the controller to the R8rt data acquisition system. And award-winning DewesoftX software makes it fast and easy to set up the amplifiers.

R8rt system delivers high-speed (200 kS/s) and high-resolution (160 dB dynamic range) data acquisition in the same instrument that is used for the test bench load analysis feedback.

High-speed data acquisition and real-time EtherCAT© output

R8rt data acquisition system combines 8 SIRIUS amplifier slices, each holding 8 high-speed analog input channels. It features an integrated industrial-grade high-performance PC computer called SBOX. 

All this in a compact chassis design featuring up to 64 DualCoreADC© (dual 24-bit) channels with a 160 dB dynamic range of up to 128 channels in a single-ADC (24-bit) configuration.

The DAQ system can be used as an all-round data logger for in-vehicle use or a test bench data acquisition device. DewesoftX software is running on an integrated, high-performance SBOX PC computer featuring an Intel i7 CPU, up to 1 TB SSD drive, and an integrated 100 Hz GPS receiver).

Dewesoft dual mode

Any SIRIUS data acquisition system equipped with an EtherCAT interface can use EtherCAT and USB interfaces to provide real-time data to a 3rd party control system and full-speed data to DewesoftX software in parallel. This makes the SIRIUS data acquisition systems a unique instrument that can be used in the control loop and as a DAQ recording device at the same time, saving an enormous cost for the customer and providing detailed insight into the process data.

Typical Dewesoft Dual Mode applications include:

• SIRIUS as an analog-to-EtherCAT® interface on a test bench with 3rd party EtherCAT® master and DAQ device for recording the data in DewesoftX software

• SIRIUS as an analog-to-EtherCAT® interface in a PLC configuration and condition monitoring device with high-frequency dynamic analysis in DewesoftX software

With the latest addition of the EtherCAT chipset, the SIRIUS data acquisition slices behave as EtherCAT slaves in parallel to the standard operation in the USB mode.

EtherCAT protocol is a standardized technology and enables hardware combinations from different vendors in the overall solution for the end-user. If the user wants to run the test bench and acquire data with DewesoftX software in parallel, the data from the R8rt data acquisition needs to be collected by two master systems:

• The MTS FlexTest (EtherCAT master) and 

• Streamed DewesoftX software on the SBOX computer

Therefore, an additional data bus is needed (USB) besides the EtherCAT to transfer the data at a high rate to the software.

This is achieved in the following manner. AD converters on the SIRIUS slices run with the acquisition rate set in the DewesoftX software. SIRIUS firmware copies the sampled data from ADC in real-time to two locations:

• a buffer for USB transfer and

• a separate buffer for the EtherCAT bus. 

The EtherCAT buffer then only holds one sample per channel and is constantly updated with the latest values. EtherCAT master can collect the most recent data at any time.

The exact moment when the EtherCAT buffer is latched and the data copied to the EtherCAT bus is controlled by the EtherCAT master. In this case, the time between those samples copied to the EtherCAT bus depends on the EtherCAT master jitter which can be up to 100 µs.

System setup

The overall system schematic is shown in figure 1. Test rig actuator control is done with the analog signals connected straight to the FlexTest. The rest of the input channels that are used for load analysis feedback on the specimen (RPC analysis) are acquired by the R8rt DAQ system and stored on the SBOX computer. The same data is also available in real-time to the EtherCAT bus and onwards to a real-time controller of the test bench.
 
Load cells and accelerometers are typically used to measure the response of the specimen. The setup of the amplifiers is done in Device Channels Setup, see Figure 3. The EtherCAT Network Information (ENI file) is required by MTS HWI File Editor to be able to add EtherCAT slaves to the hardware configuration (Figure 4). The ENI file is exported from DewesoftX software to the MTS software.

DewesoftX software – channel setup

Due to the EtherCAT bus bandwidth optimization, the data from the R8rt DAQ system sent over EtherCAT is raw and unscaled. Scaling factors are obtained from Dewesoft Channels Setup and are exported to a text file and included in the ENI file for quick import to the MTS Station Manager. The scaled data always represents the same value as displayed in the DewesoftX software. If the custom scaling is applied in the software, the scaling factor will also change to give the same physical values when applied to the raw data.

RPC drive file analysis on a multi-axis road simulator

This application with the R8rt data acquisition system was done on an MTS road simulator for testing the durability of car and truck suspension systems. It consists of 4 corners, each having 6 degrees of freedom. 104 analog input and output channels were used by the MTS FlexTest controller for actuator control. 

Additional 96 channels were used for measuring the response of the specimen to correlate the loads on the test bench to the real road load data. Signals from those channels were acquired by two Dewesoft R8rt data acquisition systems - each including 6 SIRIUS amplifier slices and streamed over EtherCAT to the FlexTest controller.

We have performed an evaluation RPC analysis test to compare the performance of Dewesoft’s solution with digital EtherCAT data transmission to an analog solution used on such rigs traditionally.

Three 3-axial accelerometers were placed on one corner of the rig with input channels distributed between both R8rt instruments. 

An exemplary drive file was played out on the corner and the response was recorded by the R8rt DAQ systems. MTS RPC Pro software was used to create a new drive file that replicated the initial run. The results showed there was no difference in the performance and convergence of the RPC Pro compared to the classical analog data acquisition.

Around 2 kilometres of expensive cabling was saved after installing the R8rt DAQ systems.

Conclusion

Standardized technology adapted by multiple vendors always opens up better solutions for the end-users. EtherCAT technology allows more connectivity with the MTS control system while the parallel EtherCAT/USB technology allows the user to use the same hardware for completely different tasks. EtherCAT solution for connecting the DAQ system with the controller can also save kilometres of expensive analog cables that are replaced by a single CAT5 cable. At the same time, the performance of the RPC analysis is the same as with the analog preamplifiers.

Complete list of the benefits of such a system:

Save money

• an all-in-one instrument for in-vehicle and test bench use

• no analog input stage is needed on a 3rd party controller due to the EtherCAT interface

• reduces kilometres of analog cables

Save time

• easy to configure - only a single cable from the DAQ system to the controller

• less chance for human errors

Improve signal quality

• perfectly conditioned signals transmitted to the test bench controller directly over EtherCAT instead of in an analog way

Analyze test bench control data

• data transferred over EtherCAT to the controller can also be recorded in DewesoftX software in parallel (Dual Mode technology)