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Hey,

I am trying to understand the terms In-run Bias Stability, Bias repeatability, and Sensitivity Temperature Coefficient from the datasheet:

• I understand that the Bias repeatability is the error of the output of the sensor that appears when you turn it on with an input of the sensor 0°/sec. Or is it the error for a long term behaviour and is defined over a long time like 1 year?
• Are these terms: In-Run Bias Stability, Angular Random Walk, Output Noise, and Rate Noise Density; different ways to define the noise of the sensor? Or is the In-Run Bias Stability a different source of noise in the sensor?
• How the parameter Sensitivity Temperature Coefficient affect the sensor? Does it affect only the output in volts some way like the following formula? Where "a" is the sensitivity temperature coefficient.

Edgard

• QUESTION

I understand that the Bias repeatability is the error of the output of the sensor that appears when you turn it on with an input of the sensor 0°/sec. Or is it the error for a long term behaviour and is defined over a long time like 1 year?

RESPONSE

Per the footnote in the datasheet:

• QUESTION

Are these terms: In-Run Bias Stability, Angular Random Walk, Output Noise, and Rate Noise Density; different ways to define the noise of the sensor? Or is the In-Run Bias Stability a different source of noise in the sensor?

RESPONSE

I am not sure I understand the different options you are presenting in this question. You could say that these metrics describe different attributes of the noise and stability of the sensor, but it would be more accurate to review their definition in IEEE-STD-952-1997.

• QUESTION

How the parameter Sensitivity Temperature Coefficient affect the sensor? Does it affect only the output in volts some way like the following formula? Where "a" is the sensitivity temperature coefficient.

RESPONSE

Sort of.  If the errors would primarily linear, then this would be true.  However, since the bias/temperature behavior is calibrated, the residual error is not linear.  The bottom line is that in this case, this is an approximation of the bias/temperature behavior.  I would use Figure 9 to see examples of the bias vs temp, rather than use the tempco spec.

• Many thanks,

In Figure 9, what are the different colours in the graph?

• Within this figure, the different colors represent the behaviors of several different parts that represent the overall population of behaviors. I hope that helps!

• Hi Edgard,

I just wanted to add a note on the questions you had about the noise metrics relating to gyro specs. One of the standard measurement techniques for gyroscopes is the measure the offset over a long period of time (hours to days, depending on the relative amplitudes and frequency content of your noise and drift terms), and then analyze it using the Allan variance technique (Allan variance - Wikipedia ). This will allow you to determine various noise contributions based on the slopes of different sections of the resulting plot (such as Angle Random Walk, which should be proportional to your white noise or noise floor as measured in a PSD, and Bias Stability, which will tell you at what point your 1/f noise contribution means continuing to average will not help you resolve your angle any further). For a rate gyroscope, Allan variance plots are interpreted like this:

Rate Noise Density is measured as the RMS of the offset in LSBs, divided by the gyro scale factor to convert to °/s, and normalized by the bandwidth.

As to your question about the sensitivity temperature coefficient, this is a measure of how the scale factor of the gyro changes over temperature, as the offset can change with temperature with both a DC term and a term proportional to your rotation rate. Ie,

Offset (T) [°/s] = (Offset (T0)(1 + Offset_TempCo) [LSBs])/(Sensitivity(T0)(1 + Sensitivity_TempCo) [LSBs/°/s]

Cheers!

• Nicely done !

Thank you!

• Thanks for your help ,

I don't understand the equation about the sensitivity temperature coefficient.  In the datasheet, there is only the parameter "sensitivity temperature coefficient".

- What is the parameter "Offset_TempCo in the equation?

- What is the value of Offset(T0)?

Best regards.

• Ah, yes, sorry, the equation I gave you above would be for the gyro without temperature calibration. However, when the gyroscopes are integrated into modules (such as the ADIS16135), a temperature calibration is performed on the offset to keep it zeroed over temperature. However, I'm not sure if scale factor is calibrated (ie, whether there is an input rotation applied at each temperature point to calibrate the scale factor changes with temperature). Assuming it is not (or that it is calibrated only to a lower order, with some residual change due to temperature), when the gyro output is converted to °/s, you would have something like:

Offset [°/s] = Offset [LSBs]/(Sensitivity(T0)(1+SensitivityTempCo*T) [LSBs/°/s])