Difference in STEVAL-STWINKT1B Time Domain Analysis output compared with Industrial VibrationMeter

Nikhil D&K · ‎2024-05-27

Hello Developers,

We are currently developing a product for industrial machines condition monitoring and predictive maintenance application. For evaluation purpose we have bought "STEVAL-STWINKT1B" for the same. We are using the "en.stsw-stwincell" cellular example for publishing stwin's data to the aws cloud. In this example for vibration analysis, on board IIS3DWB sensor is used with default sensor parameters (i.e stated below) and the Time Domain Analysis output (i.e Acc RMS, Acc Peak and Speed Rms) in all 3-axis is published on the AWS cloud after the Time Domain and Frequency Domain analysis has finished i.e after TACQ (5 seconds). And for reference measurements we are using SPM Portable Vibration meter (VIB-15) based on analog sensor, generally used in industries for measurement of true acceleration and velocity values in 1-axis of machine for condition monitioring.

Parameters used in Cellular Example:

IIS3DWB Configuration

Acc ODR: IIS3DWB_XL_ODR_26k7Hz

FIFO BDR: IIS3DWB_XL_BATCHED_AT_26k7Hz

Effective ODR: 26.9KHz

FS: ACCELERO_FS_16

HW_Filter: IIS3DWB_HP_ODR_DIV_800

FFT Parameters:

FFT Size: 1024

FFT OVL: 50

TAU : 50

Window: Hanning

TD Analysis: Speed & Accelero

TACQ: 5000 (5 seconds)

Issue:

Now we have a Compressor/Chiller/Motor equipment in Industry on which we are measuring the Acc Rms and its velocity during its normal working condition. Now as IIS3DWB sensor is digital sensor it's output is measured in all direction, but we are only taking into consideration the effective Y axis of digital sensor as it aligns with the SPM vibra meter. Now we took readings of Acc Peak, Acc Rms, Speed Rms using both STWIN kit and SPM vibra meter. But the measured reading from the STWIN are drastically different from the vibra meter (i.e almost double at higher vibrations). Also we converted the value of Acc rms into G, as the measured value of acceleration is in G for vibrameter and velocity rms have same unit of mm/s in both devices.

So i would like to know what could be the issue here as measured values are taken in similar conditions and both devices were well mounted ? Shouldn't STWIN TDM data should match or come nearby the readings of SPM vibra meter ? Or we are doing wrong thing by comparing the analog sensor output with digital sensor output although the end appplication is same.

Reference Links:

ST Win board:

https://www.st.com/en/evaluation-tools/steval-stwinkt1b.html

SPM VibraMeter:

https://www.spminstrument.com/products-and-services/portable-instruments/vibchecker/

https://3.imimg.com/data3/JU/PS/MY-1959092/vibration-meter.pdf

Setup Images for Reference:

DMORR.18 · ‎2024-07-02

Look at the attached picture to have information about the orientation of the STEVAL-STWINKT1B respect to its IIS3DWB.
After that you should take in account the axis of the IIS3DWB that has the same direction measured by the instrument you are using.
I would also like to know how you retrieve information from the IIS3DWB mounted on STEVAL-STWINKT1B since I can't see any NB-IoT modem connected.

RotondoG · ‎2024-07-02

Hi Nikhil, let me to share with you some considerations.

In the pictures we didn't see any external cellular module connected, please rememeber that the Quectel BG96 is not included in the STWIN blister and it must be purchased separately in another solution --> P-L496G-CELL02.

If I understood well you are comparing the measurement from the MEMS accelerometers embedded in STWIN with the data from a piezo. In this case for a fast analysis, with the same hardware mounted as in the pictures, I suggest to use the FP-IND-PREDMNT1, where you can see directly the accelerometer data by means of the mobile app on the phone, and as further functionality you will find also the application to send the data on the AWS Cloud through the WiFi connectivity.

This firmware package is fully documented.

Best Regards.

Nikhil D&K · ‎2024-07-02

@DMORR.18 wrote:
Look at the attached picture to have information about the orientation of the STEVAL-STWINKT1B respect to its IIS3DWB.
After that you should take in account the axis of the IIS3DWB that has the same direction measured by the instrument you are using.
I would also like to know how you retrieve information from the IIS3DWB mounted on STEVAL-STWINKT1B since I can't see any NB-IoT modem connected.

Hello @DMORR.18, thanks for the direction information. As you can see in 1st (on top) and 2nd (on side) images, we are considering the Z axis measurement of STWin as Z-axis is perpendicular to the surface on horizontal and vertical plane.

Secondly we are currently using USB to transfer ACC and Velocity rms values to serial terminal for monitoring purpose. The image was captured when we were monitoring data using BLE application but in that scenario different sensor was used. So just consider image as refference of our setup.

After some advice from other PDM forums, i have reduced the bandwidth of IIS3DWB by applying a LPF i.e ODR/20 (600Hz) and ODR/45 (1300Hz) to make the device bandwidth in range of that of Vibrameter whose range is from 2-1000Hz bandwidth. Also enabled the software high pass filter in the firmware. And by making this change, we can see most of our ACC rms values are macthing with that of Vibrameter acceleration data but still we are able to see 70-80% deviation in calculated velocity rms.

So we would like to have more clarity regarding what other configuration we can change to bring the velocity values closer.

My issue is somewhat similart to this thread: https://community.st.com/t5/mems-sensors/what-s-best-and-way-to-calculate-velocity-from-acceleration-for/td-p/104953

Nikhil D&K · ‎2024-07-02

Hello @RotondoG ,

Sorry my mistake, the image attached was just for reffference to demosnstrate our setup. Currently for monitoring the calculated acc rms and velocity rms we are using USB so after TACQ of 5 seconds the computed value will be displayed on the terminal.

If I understood well you are comparing the measurement from the MEMS accelerometers embedded in STWIN with the data from a piezo. In this case for a fast analysis, with the same hardware mounted as in the pictures, I suggest to use the FP-IND-PREDMNT1, where you can see directly the accelerometer data by means of the mobile app on the phone, and as further functionality you will find also the application to send the data on the AWS Cloud through the WiFi connectivity.

Yes, we are comparing the measurement from the MEMS accelerometer with piezo. But we are currently looking for a more accurate analysis instead of fast analysis. Thats the reason we prefered to use Motion SP based example as it gives the TDM result in 5 seconds. Duration of measurement and communication mode is not our current concern.

My issue is somewhat similart to this thread: https://community.st.com/t5/mems-sensors/what-s-best-and-way-to-calculate-velocity-from-acceleration-for/td-p/104953