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.

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