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STIM300

STIM300 is a small, tactical grade, low weight, high performance non-GPS aided Inertial Measurement Unit (IMU). It contains 3 highly accurate MEMS gyros, 3 high stability accelerometers and 3 inclinometers. The IMU is factory calibrated and compensated over its entire operating temperature range.

STIM300 is a cost-effective ITAR free solution for systems that only had FOGs as an alternative when reaching for the performance level of that STIM300 can offer.

It will be dependent of how the IMU is integrated in the user's system/application together with an algorithm.

One could check out our collaborating partner results where STIM300 is integrated: SPANBrochure.pdf

Nominal bandwidth (-3dB) Gyro: 262Hz
Accelerometer: 214Hz
Inclinometer: 17Hz

Accuracy would be the contribution from different parameters like scale factor, non-linearity, bias error over temperature, bias instability, velocity random walk and misalignment.

  • 2g: 0.5μg
  • 5g: 1.0μg
  • 10g: 1.9μg
  • 30g: 3.8μg
  • 80g: 15.3μg

The principle of operation for Sensonor gyros is based on the Coriolis Effect, or what is also sometimes referred to as the "Coriolis force". This is in the physics the comparable (or actually the same) effect as can be felt when trying to change the orientation of a rotating wheel. A force on the axis of the rotating system is felt (e.g. for a rotating wheel), and it appears (unexpectedly) to be a force applied 90 degrees offset from where applied by the user. (This effect is called precession.)

For Sensonor gyros, the dual masses of the sensor element is not rotating, however they are being excited with a movement back and forth, vibrating at roughly 9.5 kHz. The input rotation (around the sensitive axis of the gyro) results in a detecting movement, a vibration around the axis which is both normal to the excitation axis AND the sensitive input axis of the gyro. The force of the detection movement is proportional to the angular rate applied, and this is further processed and calibrated by the gyro internally in order to give digital real-time expressions for the angular rate applied.

Dual masses of Sensonor gyro element:

The principle of operation for Sensonor gyros

No. There is a high risk that it could degree the performance of the product. The housing needs the current stiffness for avoiding resonance frequencies for critical parts of the product.

If the failure requires removal of the top cover and reassembling, Sensonor cannot guarantee for the performance accordingly to the product specification and therefore not recommended to be used in application.

Sensonor standard CoC is available with each shipment for customers that require this. The CoC contain product identifications and serial number for all units in the shipment.

STIM firmware can only be updated at Sensonor.

Yes, the gyros use internal die temperature to continuously compensate the output signal.

  • Angular random walk (ARW) is improved from 0.20 to 0.15°/√h
  • Bias error over temperature gradients is improved from 30 to 10°/h rms
  • Maximum sample rate is increased from 1000 to 2000 samples/s
  • Shielded connector improves EMI capability
  • Maximum RS422 transmission bit rate is increased from 921.6 to 1,843kbits/s
  • Total delay is reduced
  • Time Of Validity (TOV) signal for external synchronization
  • Start-up time is reduced from 10 to 5s
  • Scale factor accuracy is decreased from ±2000 to ±500ppm
  • Non-linearity (200°/s) is decreased 200 to 15ppm

Bias accuracy/range is the output signal when the gyro is at rest. Bias accuracy/range specification of STIM is ±250°/h (±0.069°/s).

Bias instability is the minimum point of the Allan Variance curve over a 20 hour test period.

Bias instability is measured by Allan Variance method, according to IEEE std. 952.  

  • Modules are placed on vibration damped tables
  • Test temperature is ambient (~25°C)
  • Total measurement time is 20 hours
  • Power is applied 2 hours prior to data collection
  • Data are collected for 18 hours

ARW [˚/√h] is found at τ =1s averaging time Bias instability [˚/h] is found as lowest point of curve.

ARW is the noise component at the output of the gyroscope, derived from the Allan Variance plot at 1s averaging time.

STIM uses cascaded integrator-comb (CIC) low pass filters with linear phase response. Filter bandwidth is user selectable for each gyro axis, independent of sample rate.

Group delay is the time taken for processing the signal through the chosen low pass filter in the digital ASIC

Total delay = group delay (depending of low pass filter selected, ref. datasheet)+ 0.5ms (internal sampling of 2KHz) + delay from internal time-tick to TOV active (max 6μs)+ delay from TOV active to start of transmission (max 80 μs).

If delayed output unit is chosen 5ms must be added to the total delay.

Time Of Validity (TOV) is for synchronization of datagram transmission with external events. TOV falling edge occurs synchronous to the sample rate. Raising edge occurs after last bit of datagram.

The repeatability and the accuracy of sample rate is ±25ppm (0,0025%) over the full temperature range.

No, not directly. For calculating angle of degree the user will need an algorithm additionally to the output of the IMU. Besides angular rate the gyro can output incremental angle or integrated angle. The accelerometer/inclinometer outputs in g or in m/s/sample.

The change in angle/sample. E.g.: (100°/s)/ (125sample/s) =0.8°

Cumulative sum of angle movement/sample. Integrated angle (n-1) +incremental angle, up/down to the level of ±4°is reached then a wraparound occurs

The background for the chosen ±4° wrapping: the maximum output-rate = 480°/s, the lowest output rate = 125 samples/s -> the largest change in angle between two samples = 480/125 °/s = 3.84°/sample. The clipping range must be twice this in order to be able to differentiate between a change and a wrap. The ±4° range has been used in order to achieve the highest possible resolution.

The total angle can be kept track of by counting number of wraps, e.g.:
The following parameters/variables are defined:

  • "#wraps" is number of wraps
  • "s_curr" is current sample
  • "s_prev" is previous sample
  • "Total_angle" is total integrated angle

Add following logic/calculations:

If(s_curr - s_prev) <= -4, then #wraps = #wraps + 1
If(s_curr - s_prev) > 4, then #wraps = #wraps - 1
Total angle= s_curr + 8 * #wraps

It is dependent of the low pass filter settings from 16Hz-262Hz ref. datasheet for STIM products

1) Verify that the sample rate settings are in accordance with chosen datagram as specified in STIM300 datasheet

2) Verify that the evaluation kit is supporting the requested bit rate (ref. user manual)

Maximum sample rate

Notes:
  1. Full PC software installation. Serial hardware driver to be installed in addition

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