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The output of a fiber optic gyro contains a broadband random noise component (sometimes called "white noise") which may result either from "shot noise" or thermal noise in the photodetector. Within the gyro output bandwidth, the noise power spectral density is flat. Two equivalent units of measurement are used to describe this performance: "deg/sq.rt.-hr" or "deg/hr/sq.rt.-Hz." The conversion factor between the two is a factor of 60, and we prefer the latter unit since it directly relates the noise power to the processing bandwidth.

The output bandwidth of our gyro is set in the signal processing electronics to 100 Hz; the random noise decreases as the bandwidth is narrowed in any subsequent signal processing, with the noise decreasing as the inverse of the square root of the integration time (Alternately, the noise is proportional to the square root of the effective bandwidth). The digital output version integrates the gyro signal for 0.1 second before analog-to-digital conversion, improving the noise performance by 3.33 with respect to the analog version, without reducing the instantaneous bandwidth. A user can accomplish the same thing by integrating the analog version output for 0.1 second. The full analog gyro output bandwidth may be necessary for dynamic applications where the angular rate change is rapid or the phase response is critical, as in servo control applications.

The ARW can be measured simply by determining the root-mean-square (RMS) signal output value in the 100 Hz bandwidth, dividing by 10 (sq. root of 100) and interpreting it as an angular rate by applying the scale factor (deg/sec/mv). A more sophisticated method of determining the ARW is the Allan variance method described in IEEE Std. 647-1995.
Bias instability is the fluctuation in indicated angle rate at a constant temperature when the gyro is not rotating. This term is sometimes called bias drift, but sometimes what is meant is the Bias Offset described later. For short data samples, it is not usually possible to determine the Bias Instability as it is masked by the Angle Random Walk. For a fiber optic gyro, bias instability is a zero mean process, and the value quoted in the specification is the RMS. Along with ARW, this fluctuation in bias places a lower limit on the accuracy to which the Bias Offset can be measured, since the bias will wander during the integration time necessary to estimate the Bias Offset accurately. Measurement of this parameter is done at room temperature with a long time series of data subjected to Allan variance.
The Bias Offset is the apparent rotation rate when the gyro is not rotating about its sensitive axis (In precision applications, the user should note that the gyro does measure rotation in inertial space, and the gyro may be measuring a component of the Earth's rotation, of up to 15 deg/hr). The E-Core 1000 is a low-cost product, and uses analog components in the signal processing electronics. There are temperature-dependent offsets in some of the circuits, and this results in a deterministic relationship between bias offset and temperature for each gyro. Bias Offset is the long-term mean indicated rate at a constant temperature when the gyro is not rotating.

The gyro has a temperature sensor whose output is available in both the analog and digital versions. In a land navigation application, the bias offset can be estimated by measuring the apparent rotation rate when the vehicle is stationary. This can be subtracted from the gyro output to yield the true rotation rate. The accuracy of the estimate is dependent on the ARW, since the measurement will have a noise component for short times.
The deviation from the best fit straight line through the input rate-indicated rate data. We describe this in percentage of full-scale reading. The attached figure shows the input-output relationship of the gyro, which is desired to be a straight line, and the percentage error as a function of input rate.
This is the constant of proportionality between the actual gyro rotation about its sensitive axis and the gyro indicated output. In our gyro the output is either in volts/degree/sec (analog) or degrees/bit (digital). The digital gyro output can also be interpreted as the average rotation rate in degrees/sec/bit by multiplying the value by a factor of 10.

KVH Industries, Inc., working in close cooperation with leading GPS manufacturer NovAtel Inc., developed the CNS-5000 to offer a self-contained navigation system that combines fiber optic gyro (FOG)-based inertial measurement technology from KVH with global positioning system (GPS) technology from NovAtel. This rugged navigation solution affordably provides the precise position and orientation of a host platform on a continuous basis, even during periods where GPS signals are blocked by natural or man-made obstructions or conditions.

Through its seamless integration of KVH's FOG-based IMU with NovAtel's OEMV GPS precision receiver technology, the CNS-5000 provides a groundbreaking low-cost, small form factor solution for 3-D positioning, velocity, and attitude measurement. The deep coupling of the GPS and IMU technologies within the CNS-5000 optimizes the raw GPS and IMU data, delivering a superior position, velocity and attitude solution. Composed entirely of commercial components and rugged enough to operate in extremely demanding conditions, the CNS-5000 is also designed to meet COTS requirements. This minimizes the operational complexities for customers whose products cross international boundaries.

To learn more, visit the CNS-5000 product page.


KVH is pleased to offer world-class support and warranty coverage for all of its products. Complete details regarding all KVH product warranties are available on global support pages.


The temperature specification presumes that the gyro is mounted to a metallic surface that is at no higher temperature than the ambient air. Although a bare metal surfaces is best, a painted surface is acceptable. Surfaces with poor conduction will reduce the upper temperature limit of performance. The indicated reading of the internal temperature sensor should not, under any circumstances, be permitted to exceed 85°C (185°F).

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