STIM
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Product Documents
FAQ
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What is the principle of operation for gyros?
We manufacture MEMS vibratory gyros based on the Coriolis effect. Below is a model of the Butterfly Gyro with two masses which are driven (excited) to oscillate at a resonance frequency close to 10 kHz. When a rotation of the gyro around the sensitive axis is applied, the two masses will deflect in a direction different to the oscillation. This is called the detection motion, which ultimately gives the angular rate sensed by the gyro.
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Are the STIM products available without housing?
No, the STIM gyros are mounted to the housings before calibration which is necessary for achieving the high performance they have. Housings cannot be modified.
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Can STIM products be repaired?
We can in some cases perform FW updates. The STIM products are not designed for mechanical repair.
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Is a Certificate of Compliance (CoC) available for the STIM products?
Our standard CoC is available with each shipment for customers that require this.
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Is it possible to update STIM micro controller firmware?
The STIM firmware can only be updated by our staff at our facilities.
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Are the STIM products continuously temperature compensated?
Yes, the gyros (as well as accelerometers and inclinometers where available) use internal temperature measurements to continuously compensate the output signal.
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What is the “Time to valid data” for STIM products?
This is the time needed from power-on or reset to clearing of the start-up bit (bit 6 in the status byte). During this period the output data should be regarded as non-valid. Details for each product is given by the product specifications.
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What are the functional differences from STIM202 to other STIM gyro products?
STIM202 is designed with internal mechanical dampers for operation in environments with shocks, e.g. direct mounting on remote weapon stations. STIM210 does not have mechanical dampers and also has twice as high data output rate compared to STIM202.
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How is bias instability measured?
Bias instability is measured by Allan Variance method, according to IEEE std. 952.
Test is performed at room temperature (~25°C)
Power is applied 2 hours prior to data collection
Data are collected for 18 hours
The root Allan variance is plotted and the bias instability is defined as the lowest point of the curve.
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How is Angle Random Walk (ARW) defined?
ARW is the white (random) noise of the sensor and is read from the root Allan variance curve at 1 second averaging time.
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What type of low pass filters are used for STIM?
STIM uses cascaded integrator-comb (CIC) low pass filters with linear phase response. Filter bandwidth (-3dB) is user configurable and can be set to 16Hz, 33Hz, 66Hz, 131Hz or 262Hz.
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What is group delay?
Group delay is the processing time of the signal through the low pass filter. The delay depends on filter bandwidth.
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What is the TOV signal of STIM products?
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.
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Can the STIM products output roll pitch and yaw in degrees?
No, STIM does not operate as a standalone AHRS.
The gyros can output angular rate, or integrated and incremental angle.
The accelerometers can output acceleration, or integrated and incremental velocity.
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What is the definition of Integrated angle?
The integrated angle output is the angle since start-up or reset. The integrated angle is limited to ±4°, at which points a wrap-around occur.
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What is the definition of Incremental angle?
Incremental angle is the change in angle since the previous sample.
E.g.: (100 °/s) / (125 sample/s) = 0.8°.
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What is the accuracy of a position change measurement using STIM IMUs?
STIM IMUs does not output position, but is used in several positioning systems.
One of the leading GNSS/INS system builders obtain about 6 m horizontal position error after 60 seconds during a GNSS outage.
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What is the resolution for the different accelerometer input ranges available for STIM300?
2g: 0.5μg
5g: 1.0μg
10g: 1.9μg
30g: 3.8μg
80g: 15.3μg -
STIM Evaluation kit: The indicator for “Data arriving from device” light is green but there is no output from the STIM.
Verify that the bit rate settings of the computer serial port are in accordance with the STIM communication settings.
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How to solve evaluation kit (EVK) error message “Unable to control supply voltage”?
This error message occur when the EVK software don’t detect the startup datagrams. This happens when the STIM device is powered before the “Apply voltage” switch is flipped when connecting the STIM to the EVK SW.
Disconnect the STIM and make sure the correct procedure is followed when connecting as described by the EVK user manual.
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Do you have any example code for communicating with the STIM?
We can help with examples e.g. for converting data bytes to angular rate measurements or how to calculate the cyclic redundancy check (CRC).
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What is the CRC?
The cyclic redundancy check (CRC) is a common way of making sure the data has been correctly transmitted – i.e. that the received data is identical to what was transmitted. The STIM calculates and output a check-number based on the contents of the transmitted data itself. The receiver will perform the same CRC calculation and compare to the received CRC to verify that the transmission was successful.
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