Question, how to measure the accuracy of MMA8451Q ODR

[SLICE]

Dear team,

I would like to ask about ODR accuracy of MMA8451Q.

My customer has a doubt on the accuracy of ODR(+-2%) from their test.

The customer’s test is as below.

1. Set up the ODR=100Hz by register.
2. Set up the interruption from MMA8451Q when FIFO contains 16 data.
3. MMA8451Q will issue the interruption with 160mS period.

As a result, they saw the interruption period from MMA8451Q could exceed from +-2%.

Is their test procedure is correct for ODR accuracy measurement?

Could you show me how to measure the ODR accuracy?

Best Regards,

Miyamoto

[SLICE]

Hello TomasVaverka‌

Thank for your reply.

I will share with the customer.

Regards,

Miyamoto

[SLICE]

Hello TomasVaverka‌

Thanks for your support!

Could you show me what sigma values that the +/-2% of the typical value is?

Regards,

Miyamoto

[SLICE]

Hello TomasVaverka‌

> We don’t have any data on aging accuracy but I don’t see it deviating more than +/- 10%.

The customer thinks that semi-conductor will not degrade then it will not be deviating more than +/- 10%. Right?

If so, do you have any documentations which can back up that?

Regards,

Miyamoto

[TomasVaverka]

Hello Miyamoto-san,

As mentioned before there are no documents about aging accuracy available.

Best regards,

Tomas

[SLICE]

Hello TomasVaverka‌

Thanks for your reply!

How about the sigma number of the +/-2% typical value?

Regards,

Miyamoto

[TomasVaverka]

Hello Miyamoto-san,

I do not quite understand this question. The percentage should simply be a % of the ODR chosen. 2% of ODR 100 Hz should mean an expected deviation 2 Hz.

If this does not answer your question, please let me know.

Best regards,

Tomas

[SLICE]

Hello TomasVaverka‌

You informed me about the MAX value is related to 4 sigma.
So the customer asked me that what sigma value is related to your typical +/-2%.
In my understanding, the sigma value is deeply related to the deviation in the viewpoint of statistics.

Regards,

Miyamoto

[TomasVaverka]

Hello Miyamoto-san,

Please find below what I got from our product group:

The min max 4 sigma value is expected to be +/- 10%. So, 1 sigma is basically 2.5% of ODR. That is the typical deviation. So, ODR +/- 2.5% is the typical ODR deviation (1 sigma).  

4 sigma (10%)  is the max you could get based on the oscillator.

Best regards,

Tomas

[TomasVaverka]

Dear Miyamoto-san,

Please note that ±2% is a typical value at 25 °C.

Although customer’s method makes sense, I would recommend a simpler technique without using the FIFO. Just select the ODR, enable the data ready interrupt (INT_EN_DRDY = 1), route it either to INT2 or INT1 (INT_CFG_DRDY = 0 or 1) and then measure changes on the selected INTx pin.   .

I hope it helps.

Best regards,

Tomas

[TomasVaverka]

Hello Miyamoto-san,

I do apologize for the delay, I am double checking it with the product group and should have an answer by the end of this week.

Best regards,

Tomas

[SLICE]

Hello TomasVaverka‌

Thanks, I will wait.

Please show me the MAX, MIN and aging of ODR accuracy.

Regards,

Miyamoto

[TomasVaverka · Accepted solution]

Hello Miyamoto-san,

Here is what I received from the product group:

The min max 4 sigma value is expected to be +/- 10%.

The best way is to measure using a DRDY interrupt as you mentioned. Measure the timing between them.

You can also use one of our kits (Sensor board + MCU) and our tools log data with timestamp. That can be the quickest way to get timestamp too. 

It should be much better than 2% assuming no major temperature extremity.

We don’t have any data on aging accuracy but I don’t see it deviating more than +/- 10%.

Best regards,

Tomas

[SLICE]

Hello TomasVaverka‌

Thanks.

> Please note that ±2% is a typical value at 25 °C.

From below community thread, I understand that +2% is the Max.

Not true?

https://community.nxp.com/thread/436100 

Please let me know the maximum value.

Anyway I will inform the customer the method you gave to me.

Regards,

Miyamoto