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Tilt measurement

May 20, 2014, 6:56 am
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Hello,

 

One of my customers would like to get an indication of deposit box, and ones it achieves a tilt of 45°, he would like to get an interupt.

 

In my oppineon, the following solutions may be appropriate solution for him: ADXL343; ADXL345.

 

In these solutions is it possible to get a tilt parameter through the digital interfase? Or this parameter shall be calculated externally, by the system?

What is a calculation method of tilt? how can they apply it?

Appreciate if you can recommend additional tilt measuring solutions for this application.

 

Are there any ADI solutions that can give indication by single descrete, for example:

Tilt > 45° => Discrete='1'

Tilt < 45° => Discrete='0'

 

Thanks,

Meir

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Distortion due to aircraft engine vibrations (ADIS16364 accelerometers)

June 9, 2014, 4:40 am
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Hello,

 

we encountered an issue with ADIS16364 accelerometer readings in a unmanned aerial vehicle experiment (UAV; 20 m wingspan, 60 ccm combustion engine, max. propeller revolutions approx. 6000 RPM).

 

The sensor is attached with the standard two screws to a supporting structure, which is then rigidly attached to the aircraft frame (no damping material used). We sample the data at 50 Hz and the internal ADIS16364 digital filter is set to limit the bandwidth to 16 Hz. The problem appears, when the propeller revolutions go above approx. 3000 RPM. You can see this behavior in the PDF attached, where the propeller revolutions and norm of the accelerometer readings (x, y and z) are shown.

 

We would like to ask, what do you think is the reason of the behavior (marked by green rectangle - "area of interest") where the ACC norm drops from 1 g to 0.45 g due to high propeller revolutions (please note, that the UAV was not moving or changing orientation in this period; it was a propeller and engine test done on the ground; actual flight follows and is marked by black rectangle).

We didn't observe such behavior in the gyroscope readings. Even when the gyroscopes were simply integrated to obtain Euler angles, there was no visible evidence of such distortion.

 

Do you have any suggestions, how this can be avoided?

 

Thank you.

Jakub

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ADXRS646 drift calculation

January 21, 2013, 7:38 am
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How does one calculate the output drift for the ADXRS646? There are 2 factors given on the datasheet, i.e. the 12deg/hr and the 0.01deg/sqrt(sec). How do these factor into the calculation? Do you sum the drift due to each?

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ADXR646 Gyro drift

February 8, 2013, 9:52 am
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Mr. MEMS,

 

What Data sheet parameters should I use to predict Gyro drift? Is "Calibrated
Null" the bottom line number or do I need to calculate a number using the Alan
Varance curve?

Thanks,

Harry

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ADIS16488 zero drift problem

July 25, 2013, 1:31 am
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Hello!

My name is Aliaksei. I'm an engineer. While using IMU ADIS16488 several days ago I found out some strange feature of this IMU. I made three tests trying to compensate zero drift on Z-axis (results are logged on the picture below), but Z-axis velocity walk-down changes its direction after power switching on and makes such compensation quite difficult. I can see such strange behavior only working with Z-axis (X and Y axis are OK). Please explain this situation.      

 

I’m looking forward to hear from you.

 

z_3.bmp

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Power up rule for ADXL345

June 22, 2014, 11:38 pm
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Dear all,

 

In our product board, the product which is not started normally appeared rarely.

When the phenomenon occurs, ADXL345 is on SPI communication and does not return a response.

 

It seems that it had the ramp up problem of a power supply as a result of investigation.

A power supply waveform is as an attached file.

 

The leak current which goes via another Device-I/O from the system power was raising the power rail of ADXL345.

And then when removing the leak current, all the our product boards work normally.

 

A description is not in ADXL345 data sheet about the start up time for VDDIO, Vs and etc.

 

If there are restrictions and some notes, please let me know.

Also generally it we wish to know it even if.

 

Best Regards,

George

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Strange readings from gyro x axis on ADIS16405

May 7, 2012, 9:09 am
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Hi, I have a question regarding an ADIS16405 that I bought new last fall and have been using for the last couple of weeks. It started out that the gyro bias on all the axes were of comparable size (< .5 deg/s) and the bias stability matched the specifications. Suddenly, however, the x axis gyro has started giving a much larger bias, sometimes well over 3 deg/s, and it is not very stable. I have attached a 3-minute plot of the x axis gyro measurement from when the sensor was just sitting on my desk. I'm pretty sure something is not right about this, so I'm wondering if it means I need to get the sensor replaced or if there might be some other explanation.

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Auto Sleep Mode in ADXL313

June 24, 2014, 6:56 pm
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Hello,

 

I will use ADXL313 as alarm sensor.

Regarding to the Auto Sleep Mode, I have some question.

I checked the datasheet but, I couldn't make it clear yet.

 

1) About interrupt.

･After inactivity interrupt, it will be changed to Auto Sleep Mode.

After activity interrupt during Auto Sleep Mode, it will be changed to Measurement Mode from Auto Sleep Mode.

･Or it needs that the host(MPU) change to Measurement Mode by INT1/2(from ADXL313).(Use POWER_CTL register.)

INT1/2 will be assigned to activity interrupt by INT_MAP register.

The activity interrupt is used as only indicator during Auto Sleep Mode.

Which understanding is correct?

 

2) About Wake Up Bits in POWER_CTL register.

･This bits(data rate) will be used as timing of FIFO/Data register(XYZ) and

DATA_READY interrupt.

･Or this bits(data rate) will be used as timing of activity interrupt.

Which understanding is correct?

 

3) About updating FIFO and Data register (XYZ) during Auto Sleep Mode.

･The Data register(XYZ) will be updated with Wake Up Bits(data rate).

But, FIFO data is held in the contents of the interrupt before. (Not updated.)

･Or FIFO and Data register (XYZ) are not updated.

These data are held in the contents of the interrupt before.

Which understanding is correct?

 

4) Software compatibility (ADXL312/313)

I have used ADXL312 without Sleep Mode before.

Are both devices(ADXL312/313) have software compatibility?

 

I will evaluate with ADXL313 evaluation board soon.

And Auto Sleep Mode information is needed for Host (MPU) firmware.

 

Thanks.

TAO

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ADIS 16000 anthenas

June 23, 2014, 7:41 am
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I recently bought one ADIS 16000 and ADIS16229, but I dont know if it comes with anthenas, if it doesn´t, would you give some advice for choosing good ones, for this kind of accel?

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ADIS16209 Assembly issues

June 28, 2014, 12:55 am
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Dear Mark,

 

We have witnessed thar the power flag in all of our assembled boards in on, indicating low power. The register SUPPLY_OUT shows 2.503V.

Testing voltage right at the power in pads indicates a stable 3.3V but still the ADIS16209 SUPPLY_OUT register shows 2.503V. This can be observed in all of our assembled boards.

We have made a testing connector which can connect the 16209 on our board to your EVAL KIT, and we also made it possible to read the sensor from your EVAL KIT while supplying power from either the EVAL KIT or from our power supply.

In all cases the SUPPLY-OUT shows 2.503V.


Any ideas??


Thank you very much

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ADXL362 - SPI communication issues

June 9, 2014, 9:16 am
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Hi,

 

I'm trying to make an ADXL362 talk to a microcontroller (the nRF51822-Eval borad). I am trying to read the 0x00 register, therefore I send 0x0B and then 0x00.

 

As you can see in the attached, ADXL362 doesn't respond with 0xAD. It seems that at the end of the second clock burst, ADXL362 rises the MISO but it doesn't keep it up until the following clock burst.

 

MOSI appears to work OK.

 

SPI is set to mode 0 at 1Mbps.

 

Any ideas?

 

Thanks

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ADXL362 X,Y,Z values ...

March 27, 2013, 1:33 am
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Hi,

I writed a little driver for the adxl362 accelerometer (sparkfun pcb),

but, with the sensor stationaryon the desk, I read values, along Z axis,

greater than 1000 mg ... I' ve attached 3 pictures that shows the accelerations

at different Bandwidth filter values; the Vc/Vd is 3.3 V for all tests.

 

My simple question is: are these values correct ? Is the sensor damaged, or

the single capacitor on the pcb, is insufficient to filter the noise ?

 

Best Regards

Leonard

 

PS: the T value is about 22 °C

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ADXL362 trouble

May 17, 2013, 2:06 am
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I‘m trying to use the ADXL362 now. I haven't read the X Y Z axis acceleration data yet. What I want to ask is ,does it necessary to pull up the SPI pins to the VCC ? Because in the datasheet (chianese version, see below) it said there is no pull up or pull down resistance inside the IC? On my board there is no  pull up resistance!

 

1.PNG

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ADXL362 current

June 30, 2014, 11:05 am
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I am putting the ADXL362 into wake-up mode, but instead of drawing 0.27uA, it is drawing 2uA.

 

I am using the following instructions to put it into wakeup mode:

 

    SPIwriteTwoRegisters(0x20, 300);

    SPIwriteOneRegister(0x22, 10);

   SPIwriteOneRegister(0x27, 0x03);

   SPIwriteOneRegister(0x2A, 0x90);

    SPIwriteOneRegister(0x2D, 0x02);

 

On the MCU I have the MOSI pin as OUTPUT

SCK pin is OUTPUT

slaveSelectPin is OUTPUT

MISO pin is INPUT_PULLUP

Interrupt pin is INPUT_PULLUP

 

After putting it into the wakeup mode, I have

 

digitalWrite(MOSIpin, LOW);

digitalWrite(SCKpin, LOW);

digitalWrite (MISOpin, HIGH);

digitalWrite (slaveSelectPin LOW);

 

I am not writing anything to the interrupt pin.

 

Is this right?

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ADIS16209 Accuracy Problems and Assembly issues

June 19, 2014, 5:46 am
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Hi,

 

we have a program in which there is an ADIS16209 as the mail tilt sensor.

we have tested several units via the evaluation board and they performed to spec.

we had made a PCB design which includes the ADIS16209 on-board (according to app notes and the datasheet rev-c).

in this architecture the ADIS is getting stable and filtered3.3V from a switched DC/DC converter (ripple is lower than 15mV)

we had made 10 assemblies via automated SMT. from the 10 units only 3 ADIS units were functional!!

we had x-ray tests to see the solder on the pads and the solders were looking good but the units were none functional.

we had opened a new and seals batch of components and made another 7 SMT units built (taking the soldering profile, SMT aliment etc' under great care).

in this batch we had all 7 working but not according to spec or expectations...

we configure the SMPL_PRD to 41 and the AVG_CNT to 8 (the max value) and our testing facility's temperature is 23C-25C:

here are some questions:

  1. in all 10 units were experiencing jitter of about 4-6 LSB in total stable conditions - in the Evaluation units the jitter were about 1-2 LSB
  2. in most units we have a drift in measurements that behaves as if the sensor is measuring a larger angular degree:
    for example: we have a measuring jig which is leveled to 0.1mRad and there we have accurate wedges for 5, 10 and 15 degrees, those wedges are also very accurate. the PCB with the ADIS16209 is placed on a metal bracket with leveled planes which are placed on the testing equipment.
    we see a measurement drift of about 0.05 degree per every angular degree, meaning, for every actual 1 degree our ADIS16209 sensors are measuring 1.05 degree, therefore 5 actual degrees are measured as 5.25, 10 actual degrees are measured as 10.5 and 15 actual degrees are measured as 15.75, etc'
  3. we have larger deviation in the positive side than in the negative side - for example we measure -14.5 and +15.7 at actual 15 degrees
  4. we see that the Y incl axis has significantly higher errors than the X incl axis (the data above represents the Y axis were the X axis shows about 20% less deviation....)

we had gone through all calculations, checked and rechecked the SPI interface and we are currently in a very problematic situation - we have some 100 units which we are not assembling because we don't know why the first 10 are not operating according to expectations....

 

waiting for any help possible!!!

 

Thanks

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ADXL362 Z-axis unstable when measuring static acceleration

September 16, 2013, 8:45 am
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I wrote a program to continuously read X,Y,Z acceleration values from the ADXL362 and I'm noticing some strange results when the chip is stationery. My chip is positioned horizontally on a flat surface. I'm measuring "static" acceleration so I expect to see only 1g on the Z axis from the force of gravity. However i notice that my Z axis acceleration jumps from 1g to 0g back to 1g on consecutive reads. Has anyone else seen this behavior/ can anyone explain this? I've attached a screenshot of what my data looks like.

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ADXRS810?

May 20, 2014, 7:35 am
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MEMS performance specification and validation

May 22, 2014, 4:52 am
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Hi!

 

I send the following questions to analog technical support an I was redirected here. Hope you can help me!

 

"I'm doing a bachelor degree study on MEMS performance specification and validation. I have a few questions considering your products:

 

Accelerometers

-How do you define the typical values? For example ADXL350 has ±0.24 mg/C typical 0 g Offset vs temperature (Z-axis). What are the sigma variation limits for typical values or is there any? ±1 sigma perhaps?

 

-Do all the MIN/MAX specifications represent a mean ±3sigma distribution? (you mention it only for 0g offset vs temp min/max values)

 

-Is nonlinearity value calculated from bestfit straight line or endpoint-fit line?

 

Gyroscopes

-Again, how are the typical values calculated and what population do they represent? For example ADXRS450 has sensitivity tolerance of ±3% but there's no mention of the variation limits.

 

-Does the sensitivity tolerance include lifetime drift and calibration errors, or temperature error only?

 

 

Wow, kind of a lot of questions after all.. Hope you can answer them soon and precisely

 

Thanks in advance!

 

Br, Iivari Heikkilä"

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How to make IMU sensors insusceptible to surrounding electronics?

June 5, 2014, 9:06 am
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Hi,

 

I am using two IMU sensors to perform the same tests and they are: ADIS16360 and ADIS16362.

 

I attached my IMU sensor on a robot arm to take some data and the gyroscope measurements were always out of calibration after one or two trials. I took the data with EVAL-ADIS board. The robot's control box is about 2 feet below the arm on which the sensor was attached to. I currently have my sensor wrapped in layers of aluminum foil but that wasn't helping either. Is there something I can do to prevent this?

 

Thanks,

Dao.

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ADXL362 axes of acceleration sensitivity - typo?

May 10, 2013, 9:34 am
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In the ADXL362 datasheet (rev B) the expected outputs for X and Y are not the ones I see on my device.

 

adxl362.png

 

For example, when the pin 1 dot is pointing down (in the same direction as gravity), my device reads roughly -1g in Xout. In the diagram, it's shown as +1g. Is this a typo? The expected Z axis output in figure 51 is correct. I noticed in the datasheet for the ADXL345 has a similar diagram, and that the expected outputs for X and Y are negated compared to the ones in figure 51 for the ADXL362. I assume Analog Devices wouldn't change the convention, and that this is a typo in the 362 datasheet.

 

And yet, the figure 50 caption says corresponding output increases when accelerated along the sensitive axis. I took that to mean that if gravity was pointing along the Ax axis in figure 50, that Xout would read 1g, like figure 51 says. But it reads -1g. What's going on?

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