I have got 2 new IIS3Dwb IC from same lot , I made custom PCB for those, connected to shaker and getting acceleration values and showing it through my own developed application.
Problem: Z axis seems defecting /sensitive much higher than x and y axis irrespective of vibration direction orientation.
When no vibration present every axis values seems ok and showing 1g level of gravity.
Both ic s showing same issue
Tried magnet, glue mount but no improvement.
Tried different vibration source , different vibration frequency
Changing pcb orientation didn’t help.
Not using int pins, mcu controlling sampling speed 12.5 khz sampling speed and 6.3khz bandwidth with 16g sensitivity.
Using single axis mode, fifo disabled
Pcb layout below.
When no vibration getting 1g so I believe my g conversion math is ok.
Below is my code in arduino IDE ( not complete code pasted due to length)
//IIS3DWB
#define IIS3DWB_WHO_AM_I 0x0F // should be 0x7B
#define IIS3DWB_CTRL1_XL 0x10
#define IIS3DWB_CTRL3_C 0x12
#define IIS3DWB_CTRL4_C 0x13
#define IIS3DWB_CTRL5_C 0x14
#define IIS3DWB_CTRL6_C 0x15
#define IIS3DWB_CTRL7_C 0x16
#define IIS3DWB_CTRL8_XL 0x17
#define IIS3DWB_OUT_TEMP_L 0x20
#define IIS3DWB_OUT_TEMP_H 0x21
#define IIS3DWB_OUTX_L_XL 0x28
#define IIS3DWB_OUTX_H_XL 0x29
#define IIS3DWB_OUTY_L_XL 0x2A
#define IIS3DWB_OUTY_H_XL 0x2B
#define IIS3DWB_OUTZ_L_XL 0x2C
#define IIS3DWB_OUTZ_H_XL 0x2D
#define IIS3DWB_FIFO_CTRL4 0x0A
----then---
SPI.begin();
SPI.beginTransaction(SPISettings(5000000,MSBFIRST,SPI_MODE3));
writeRegister(IIS3DWB_CTRL1_XL,0x04); // power down and 16g mode
writeRegister(IIS3DWB_FIFO_CTRL4,0x00); // disable fifo
writeRegister(IIS3DWB_CTRL8_XL,0x00); // low pass 6.3khz
writeRegister(IIS3DWB_CTRL6_C,0x01); // single axis mode start with x
writeRegister(IIS3DWB_CTRL1_XL,0xA4); // power on again and 16g mode START WITH 16G
---------then -----
SPI.begin();
SPI.beginTransaction(SPISettings(5000000,MSBFIRST,SPI_MODE3));
writeRegister(IIS3DWB_CTRL1_XL,0x04); // power down and 16g mode
writeRegister(IIS3DWB_CTRL6_C,0x01); // single axis mode x axis
writeRegister(IIS3DWB_CTRL1_XL,0xA4); // power on again and 16g mode START WITH 16G
delay(50);
for(int j=0; j<2048; j++){ ///////loop
////TURN ON ACC
//
memset(rawData, 0, sizeof(rawData)); // reset
readBytes(IIS3DWB_OUTX_L_XL, 6, &rawData[0]); // Read the 6 raw accel data registers into data array
x = (int16_t)(((int16_t)rawData[1] << 8) | rawData[0]) ; // Turn the MSB and LSB into a signed 16-bit value
// make a string for assembling the data to log:
accvalue[j] = x;
}
SPI.end();
------then smilarly for y and z-----
SPI.begin();
SPI.beginTransaction(SPISettings(5000000,MSBFIRST,SPI_MODE3));
writeRegister(IIS3DWB_CTRL1_XL,0x04); // power down and 16g mode
writeRegister(IIS3DWB_CTRL6_C,0x03); // single axis mode z axis
writeRegister(IIS3DWB_CTRL1_XL,0xA4); // power on again and 16g mode START WITH 16G
delay(50);
for(int j=0; j<2048; j++){ ///////loop
memset(rawData, 0, sizeof(rawData)); // reset
readBytes(IIS3DWB_OUTX_L_XL, 6, &rawData[0]); // Read the 6 raw accel data registers into data array
z = (int16_t)(((int16_t)rawData[5] << 8) | rawData[4]) ;
prevCycle = startCycle+6350;
delay(10); /// sampaling timing controll
// make a string for assembling the data to log:
accvalue[j] = z;
}
currentMillis =micros()-bMillis;
accvalue[2050] =currentMillis;
////TURN OFf acc
//SPI.end();
-----------some more functions -----------
////// accelerometer access fuction
void readBytes(uint8_t reg, uint8_t count, uint8_t * dest)
{
digitalWrite(accspi, LOW);
SPI.transfer((reg & 0x7F) | 0x80);
SPI.transfer(dest, count);
digitalWrite(accspi, HIGH);
}
void writeRegister(char registerAddress, char value) {
digitalWrite(accspi, LOW);
SPI.transfer(registerAddress);
SPI.transfer(value);
digitalWrite(accspi, HIGH);
}
I compared IIS3dwb output with LIS3DSH output placing same place same orientation , when shaking at 500 hz lis3dsh showing y axis is having high g and its correct as shaker is shaking in Y axis. However IIS3dwb showing Z axis is sensing higher g values than y axis. Which is surely not true. To crosscheck I changed axis orientation against vibration orientation, but still z axis is sensing high g
Thanks for reading any help appreciated.
@Eleon BORLINI Thanks a lot for your reply , I have tested as per you suggestion .your question answer below
Did you try to configure the 3 axis mode (enabling the bits in CTRL6_C (15h) named XL_AXIS_SEL[1:0] = xxb (11 = Z-axis);
= yes only noise increased but z axis still deflecting high
Did you try to configure the BDU bit in CTRL3_C (12h) register? With this bit the output registers are not updated until MSB and LSB have been read)
= yes but nothing changed
You wrote: >> Not using int pins, mcu controlling sampling speed 12.5 khz sampling speed and 6.3khz bandwidth: this means that the sampling frequency is less than double of the device bandwidth, so I'm concerned whether the signal can be properly reconstructed and, if there is some issue, aliases effects can rise --> could you try to increase the sampling speed from MCU side (even if you are shaking at 500kHz)? Note also that IIS3DWB ODR is fixed to 26.667kHz.
= datasheet mentioned that "Ultra-wide and flat frequency response range: from dc to 6 kHz (±3 dB point)" so I kept bandwidth on that limit.
I tried high sampling speed 26 Khz ( bandwidth of 13khz ) but results is same high z vibration, I am shaking at 500hz not 500khz btw
There could be also the possibility that the spikes you see are true: in the LIS3DSH case the maximum ODR speed is 1600 Hz, while in the IIS3DWB case you have a fixed, high rate of 26.667kHz, so it's possible that the spurious spikes are above 1600Hz, but can be detected by ODR speed of 26.667kHz.
= if you check fft images vibration is at 500 hz which is in range of both lis3dh and iis3dwb and there is no powerful spike after 1000 hz as captured by iis3dwb . if we just compare iis3dwb x axis and z axis z is much powerful than x at 500hz itself so we can ignore higher frequency spikes right?
please note i have checked changing orientation of axes if source z axis really having high vibration then after rotating iis3dwb 90 degree , x or y axis vibration should be increased right? but z axis always showing high sensitivity in what ever angle I connect to vibration source.
The Z axis might have a higher offset than the X and Y ones: you can try with compensating the offset configuring the OFF_Z (12h) register.
= I think offset is not issue here while z in parallel with earth (1g) while no vibration its showing 1g. if we apply vibration z axis defecting (up down) keep 1g range in middle. please check time vs g graph image. similarly after rotating 90 degree or any other degree offset also get changed but still Z axis showing high movement.
You can try configuring lower than 16g Full Scale, such as 4g and 8g, and check the behaviour.
= yes I tried 2g mode 4g mode but that did not solved the issue.
here comparison image of lis3dsh vs iis3dwb at same vibration source same orientation same location
waiting for you further help
@Eleon BORLINI @Douglas MILLER
hi again, you misinterpret my question this time
1> I am not using IIS3DWB with industrial vibration meter rather I am trying to make a new vibration meter with IIS3DWB which can output (vibration velocity mm-s)
2> I know how to convert LSB to Acceleration ( g ) and please check top image z axis values are near 1g when stable.
now back to the main issue
I re ordered 2 new ICs from mouser electronics replaced old IC
after testing got same problematic result ( X axis , Y axis ok but z axis vibration amplitude is much higher than actual
I also ordered STEVAL-MKI208V1K as per you suggestion connected with my processor but got same problem
so as the IC is already soldered we can eliminate IC damaged during hot Air soldering
so let me summarize
1> its not calculation error ( lsb to g ) as 1g can be seen when no vibration
2> its not offset error ,connect to vibration source in any direction but z axis movement always high
3> hardware (IC) is ok
as per data sheet this ic is for industrial application purpose like vibration monitoring so is that applied in anywhere? by anyone? can i get some real life case study documents ? am I only one facing this issue ?
I think developers of this IC can answer
I do not know why st support is taking too long to response
