Frequently Asked Questions

General Questions

Q – What do the terms in your specifications mean?

Q - How do I calculate angle position from the angular rate data retrieved?

Q - What differentiates the Silicon Sensing products from your competitors?

Product Questions

Q  – Do need to be careful when designing my power supply for the CRS03 to make sure that the supply voltage ramps up at a certain rate?

Q – Storage temperature in CRS03 and CRS05 datasheets is <110 C. Does that mean, that even short term overburn to 125 C (<1 hour without power) may damage this device?

Q – How do you mount a CRS05?

Q – Can I mount a CRS03 on the bottom of the camera to stabilise its movement?

Q - How does CRS10 performance degrade over time?

Q - How does CRS10 perform in terms of bias repeatability and residual error after I apply thermal compensation?

Q - How is the CRS10's analogue output derived from the digital output?

Q - How is the CRS10's analogue output degraded compared with the digital output?

Q - What is the resolution of the CRS10's outputs?

Q – What do the terms in your specifications mean?

A – See our Glossary section for full explanations of each term.

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Q - How do I calculate angle position from the angular rate data retrieved?

A - The angular rate sensor gives an output, which is proportional to the rate of turn and, therefore, to create a measurement of angle requires integration with respect to time. The error terms in the integration are the error in the Scale Factor, the Noise and the Bias of the sensor.  For a constant Scale Factor error, and where the mean angular position over time is zero (such as in an oscillatory system), the error then becomes the integration of the Bias, Noise and Linearity over the time period of measurement.  For the effects of Noise, see Angular Random Walk in our Glossary.

A typical specification for rate sensor Bias is 3°/s maximum so, if no calibration is performed, the angular error due to Bias will build up at the maximum rate of 3° for every second of movement. This can, however, easily be improved if the host system has the ability to subtract the Bias offset before measurement begins.  After start-up and at constant temperature, the bias variation could be less than 0.05°/s per 5s.  Subtracting that initial Bias (3°/s) and carrying out the same integration will result in an angle error that builds up at 0.125° per 5 seconds of movement.

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Q - What differentiates the Silicon Sensing products from your competitors?

A - Our sensors have very low bias drift with time and temperature, are very repeatable (allowing for thermal compensation to achieve high performance), are virtually impervious to shock and vibration, and have a wide operating temperature range.  This is achieved by using a balanced vibrating silicon MEMS ring as the sensing element, as opposed to cheaper unbalanced vibrating comb or tuning fork sensors.

CRS sensors, include a double closed loop control circuit to maintain amplitude and frequency, others are open loop.  Clearly this specification can add cost.  You may not need all of this performance, in which case we may seem expensive.  However, we have many customers who have switched from our competitors to our sensors, because they can offer greater value: the cost of manufacture of the host product can otherwise increase due to low yield, the cost of screening gyros and, in extreme cases, field failures of cheap gyros have increased warranty costs, and damaged sales by creating a poor image of their product.  You have to look at the overall requirement and cost, to judge whether, in the long run our gyro is more costly.

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Q  – Do need to be careful when designing my power supply for the CRS03 to make sure that the supply voltage ramps up at a certain rate?

A - Yes.  The supply voltage must reach its nominal 5V in less than 5ms, otherwise the gyro may latch-up and will provide no output.  In this condition is does not automatically reset.

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Q – Storage temperature in CRS03 and CRS05 datasheets is <110 C. Does that mean, that even short term overburn to 125 C (<1 hour without power) may damage this device?


A - No. Short term overburn is OK at 125 degrees centigrade.  However it is important not to take it beyond 130 degrees centigrade.

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Q – How do you mount a CRS05?

A - One of the best ways to mount a CRS05 is by making a mechanical mount that includes card slots into which the CRS05 package can be slid before soldering its pins into (say) a motherboard assembly.  To mechanically support the CRS05 by its soldered pins only risks fatigue failure, axis alignment accuracy and susceptibility to vibration and should thus be avoided.

The sensor head of the CRS05 (the metal can) also provides a reference surface at the top of the can lid so it is also possible to glue (or otherwise pot) the CRS05 into a suitably sized hole.  For a robust solution, the whole of the CRS05 can be potted into a larger assembly.

Depending on the level of shock and vibration seen by the customer's application, it could be okay to use the four 0.8mm holes in each corner of the circuit board for mounting CRS05.  The pads surrounding these holes are not electrically connected to the sensor, so they can be used to secure the gyro board to suitable supporting pins by soldering.  We suggest that pins with a shoulder are used to ensure accurate alignment of the sensor to the customer application to prevent the possibility of cross-coupling and to give clearance for the components.

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Q – Can I mount a CRS03 on the bottom of the camera to stabilise its movement?

A - Many customers use our single-axis gyro sensors to stabilise platforms, including camera platforms.  Unfortunately it is a little bit more complicated than simply attaching the gyro.  The sensors measure angular speed and give an analogue output proportional to the angular input speed.  To stabilise a camera you need a 2-axis platform and a sensor on each axis (pan and tilt).  The sensors then provide feedback into a closed loop controller for driving the platform motors.

So the CRS sensors form only one part of a stabilising system that must also include control (a computer or similar) and actuation (motors or other correcting devices).

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Q - How does CRS10 performance degrade over time?

The performance of CRS10 is unlikely to degrade appreciably over a 15 year life.

There are two characteristics to the transfer functional of any block of any system: the DC or "bias" state and the AC or "gain" state.

Changes in the DC characteristics of any part of the VSG-4 system (the fourth generation Vibrating Structure Gyroscope technology used in CRS10) are eliminated because all of the data occurs at the ring frequency, (14kHz). The information content of the signal is "double sideband suppressed carrier (DSSC)". i.e. there is no DC information generated. Therefore, DC drift is immaterial unless it becomes so large that the system saturates – which is detected in Continuous BIT.

Changes in the AC characteristics are accommodated by using the system as a closed loop, force rebalance device. As the force is rebalanced, the error terms are effectively multiplied by zero. There is only one signal path with gain, and that is through the single ADC. Changes in the AC characteristic are eliminated by running all of the pickoff information through a single signal conversion path. One of the signals within the path is an AGC control of the ring amplitude. Therefore, any change in gain will be servoed out by the ADC, leaving all other gain terms unaffected.

As all of the processing is digital in CRS10, there are no offset or scaling errors associated with the rate loops themselves; the numeric values are not subject to drift or error; "multiply by x" cannot become "multiply by a slightly different x". Similarly, the performance of the system functional blocks cannot change with time, being purely digital in nature.

All of the useful information is extracted digitally from the DSSC, demodulated in the digital domain. Therefore there are no demodulator phase errors; the entire gyro processing system is synchronised to a master clock, being the mechanical resonator itself. Variations in timing with temperature are therefore also slaved to the ring, resulting in virtually perfect demodulation irrespective of temperature. The stresses on the resonator are very small, and its wafer – level vacuum encapsulation isolates it from any environmentally induced changes.

Caution: other MEMS gyroscopes, including the tuning fork type, may use open loop and non-force rebalance technologies which means that they may be prone to performance degradation over time.

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Q - How does CRS10 perform in terms of bias repeatability and residual error after I apply thermal compensation?

The simple answer is that the post-compensation bias repeatability of CRS10 is exceptionally good.

CRS10 as a product is internally compensated by means of its own internal algorithms, using a generic temperature fit. The customer may then optionally compensate an individual gyro against temperature for enhanced performance. Following that compensation, the residual error will be derived from imperfection of fit and any thermal hysteresis. The graphs linked here show the UNCOMPENSATED performance for a sample of five gyros: <link>

As can be seen, there is a performance change from sample to sample, but this will be taken out by the customer calibration, provided that sufficient steps in the look-up table are employed, (piece-wise linear method).

Having performed this PWL compensation, the worst case hysteresis observed for this set of gyros is 0.22 deg/s, (pk-pk).

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Q - How is the CRS10's analogue output derived from the digital?

The digital output is passed through a digital scaling stage on to a 12-bit DAC and out through a ratiometric output buffer.  The scaling stage is dependant upon rate range selected.  The internal BIT signal is summed into the output such that the analogue response is clamped to 0V during failure conditions.

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Q - How is the CRS10's analogue output degraded compared with the digital output?

The analogue output is not deliberately degraded but errors in the DAC and output buffer must be taken into account, so theoretically the noise and output bias are potentially higher.  Additionally, the analogue output is ratiometric and so half of any supply noise or supply voltage variations will be evident at this output.  The analogue output is updated at 3.5 kHz (nominal, resonator dependant) whereas the digital output can only be read at a maximum of 1 kHz which can introduce measurement differences should the two outputs be compared directly.

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Q - What is the resolution of the CRS10's outputs?

The analogue resolution is dependant upon the selected rate range.  The resolution for the ±75°/s default range is 0.042°/s, and all others are proportional to this figure, e.g. ±50°/s range has a resolution of 0.028°/s.  Bear in mind this is a ratiometric value and has been calculated assuming a +5V sensor supply.

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