The following is a list of question and answers that have been asked by customers and which may be useful to others using Silicon Sensing products in their engineering designs. If your query remains unanswered please either contact your distributor or click here to contact Silicon Sensing.
Our gyroscopes use a ring as the vibrating structure suspended by legs around the ring. This means that the sensor is balanced and symmetrical and therefore shocks and vibration will not cause any undesirable motion that would be observed in a non-balanced structure such as a tuning fork. For normal operation, any deflection of the ring will not cause an impact to other components because the clearances are large.
Please see our Glossary section for an explanation of each parameter or term. If you need additional help or clarification please contact us using the website.
A ratiometric output means that the output of the gyroscope is proportional to the supply voltage.
Gyroscopes measure angular rate in space, without reference to any fixed point and will sense angular rate about its sensitive axis, at all orientations. The gyroscope is also very insensitive to gravity and can therefore be used in any attitude.
We do specify sensitivity to gravity and linear acceleration, but because our gyros use a balanced ring as the vibrating structure, they are very resilient to gravity, linear acceleration and vibration.
Resolution means different things to different people depending on their application and use of the gyroscope.
If the gyro has a digital output, then the resolution is taken as the least significant bit of the data in the message. This resolution depends on the rate range the gyroscope has been set up for. The datasheet provides the scale factor in terms of lsbs/°/s. The reciprocal of this number gives the weighting of the lsb, or the digital resolution. Resolution can be improved by applying over-sampling techniques. These techniques usually involve sampling the output at a very high rate and averaging to improve the resolution.
If the analogue output is used, then the best resolution achievable can be taken as either the bottom part of the Allan Variance plot, i.e. the bias instability for the device. An alternative definition for analogue resolution is the minimum observable difference observable at the output for a change to the input. This is related to noise and is normally taken as the input signal which will cause an output to be greater than the noise output.
The Vibrating Structure within our gyroscopes has a resonance at about 14KHz or 22KHz, depending on the gyroscope. Noise on the power supply around this frequency or harmonics of this frequency may couple into the signal and cause additional noise. If there are periodic signals around these frequencies, such as that produced from switched mode power supplies, beating may be observed in the gyroscope output.
Please see our Glossary section for an explanation of each parameter or term.
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 (SF) and the (total) Bias (B) of the sensors. For any volts (V) output from the sensor, the angle is computed as:
Integral [ ( V (SF +SF ERROR) + B) ]dt, from T0 to T.
For a constant SF 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 Total Bias over the time period of measurement..
A typical specification for the Rate Sensor Bias is 3°/s maximum so, if no calibration is performed, the angular error 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.
We specify performance over a defined operating temperature range for the product. The device will normally operate outside of this range but we cannot guarantee function or performance, since we only test the device over the specified operating temperature range. When the device is not powered, it can be exposed to higher temperatures for short durations. At 130°C, there is a glass transition change within the device, which will reform when the device cools down, but the characteristics of the device are likely to change. It is therefore important not to expose the device to temperatures close to 130°C.
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.
Our gyroscopes are either manufactured in Japan or in the UK. In Japan, they are manufactured at Silicon Sensing Products which is located at the same address as Silicon Sensing Systems Japan, inside the Sumitomo Precision Products complex. In the UK, they are manufactured at our Plant in Plymouth, Devon.
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.
If the gyro has a SPI output, then the answer is yes. This is one of the features of an SPI bus. The “Slave Select”, (SS) pins are used to select each individual device.
The general answer is no. They have been designed for high volume applications with a superior performance to cost ratio. It is therefore not economic to consider repairing a damaged device.
Yes, indeed, our gyroscopes have been used by a number of our Customers for such applications. Low noise coupled with high resilience to shock and vibration makes them an ideal choice. The Gyroscopes will measure the angular rate and provide an output proportional to angular motion on the camera. This signal can be used to drive servo motors to keep the camera pointing in the desired direction or maintaining the desired angular rate, removing the unwelcomed disturbances. Alternatively, the signal can be applied to the video signal or image to displace the signal, compensating the unwelcomed disturbances in the process.
No. If you use the analogue output of a gyroscope, we recommend using an anti-aliasing filter in the signal path to the analogue to digital converter (ADC), to reduce the aliasing of noise to in-band frequencies.
Basically, our gyroscopes use a silicon (MEMS) ring which is setup and controlled to vibrate in a precise manner. When the gyro is rotated, the resonance pattern changes; the way it changes being proportional to the rotation rate applied to the gyro. Electronics around the ring control the resonance of the ring and also sense the motion of the ring.
When the gyro is subjected to changes of temperature, the bias and scale factor of the gyroscope can change.
We therefore provide two outputs which can be used to sense the change of temperature.
A temperature sensor is included to sense the temperature of the electronics within the gyroscope.
The ring's resonating frequency is also sensed and output as a digital signal. The frequency of the ring is proportional to the temperature of the ring. The frequency of the ring is proportional to the temperature of the ring. This ring frequency is nominally 14 KHz, with the FRQ signal being two times this frequency, that is , nominally 28 KHz. The frequency changes with temperature at -0.76 Hz/degC.
By subjecting the gyroscope to a changing temperature, it is possible to measure the errors (bias and scale factor) of the gyroscope against the frequency output and the temperature sensor output. Using look up tables or fitting polynomials to these errors, it is possible to compensate for the errors, by subtracting the derived error from the output of the gyroscope.
The temperature sensors will be more responsive to changes in temperature of the environment than frequency because of the longer thermal path to the MEMS ring. Equally, in a highly (angular) dynamic environment where the ring will be heated by the nulling action of the secondary loop, the frequency output will be more responsive. In a fairly stable environment, where the temperature across the whole of the gyroscope is stable, then both
methods are equivalent.
In general terms, the simplest method for temperature compensation is to use the on-board temperature sensor as the first step. This can be regarded as the primary (coarse) thermal error correction. A further refinement of thermal compensation can be achieved using the ring frequency (FRQ) since this is a measure of the temperature of the ring.
At normal room temperature (+25degC) operation, the FRQ signal is between 27.4kHz and 28.6kHz. The ring gets 'stiffer' as the temperature drops and thus the frequency will increase, and vice versa. The temperature coefficient of the ring is between -0.82 and - 0.70Hz/degC (nominally -0.76Hz/degC). So, if the value of FRQ drops by, say, 7.6Hz then you can assume the ring temperature has increased by 10degC to +35degC [-7.6 / -0.76 = +10degC]. The silicon ring is supported on a glass substrate surrounded by an inert gas inside a sealed metal can. So it is quite well insulated, thus there is a lag between a change in the ambient temperature and the temperature (and thus frequency) of the ring. The temperature sensor on the board reacts quicker to the ambient temperature fluctuations.