View Full Version : How does a 'Quartz' AHRS AHC work? (Collins 86)
Hello Everyone!
Long time reader, first time poster.
I'm trying to figure out how a 'Quartz' AHC works and why it would be used instead of a laser ring gyro.
The plane I'm flying uses Collins AHRS-86 technology, and the manuals I have available just makes reference to the Attitude Heading Computers inertial sensors. From Collins web site, I gather that they tend to use quartz gyros, while Honeywell uses laser ring gyros.
Thanks guys, I enjoy reading all your posts and when I have a bit more experience, I'll start adding to them.
FTP
rigpiggy
7th Jul 2008, 01:10
Fairly simplistic answer. basically three tuning forks on the affected axes, long/yaw/lateral. a flux valve and a gravity switch, with a whole lot of PFM thrown in. After the boot up alignment at rest, it basically is a doppler system in operation ie: reads acceleration due to different frequencies. acceleration on any of the tuning forks is transmitted to a piezo electric crystal which puts out a small electrical charge proportionate to bending stress. the computers reads the charges as accelerations and signals the processor on the EADI/EHSI, the gravity and flux valves take care of normal precession.
Not a wholly scientific answer, but hopefully gives a basic understanding
Quartz rate sensors
This system is usually integrated on a silicon chip. It has two mass-balanced quartz tuning forks, arranged "handle-to-handle" so forces cancel. Aluminum electrodes evaporated onto the forks and the underlying chip both drive and sense the motion. Since quartz is dimensionally stable, the system can be accurate.
As the forks are twisted about the axis of the handle, the vibration of the tines tends to continue in the same plane of motion. This motion has to be resisted by electrostatic forces from the electrodes under the tines. By measuring the difference in capacitance between the two tines of a fork, the system can determine the rate of angular motion.
Brian Abraham
7th Jul 2008, 01:23
You may find a reading of the patent of interest Quartz rate sensor - Patent 4516427 (http://www.freepatentsonline.com/4516427.html)
If you place any faith in wiki Quartz crystal microbalance - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Quartz_crystal_microbalance) and Inertial navigation system - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Inertial_navigation_system)