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Thesis - Leigh Moody.pdf - Bad Request - Cranfield University

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Chapter 3 / Sensors / Helmet Mounted Sight<br />

_ _<br />

D<br />

Z ~<br />

: =<br />

AD<br />

ϕ<br />

LIM<br />

AD<br />

AD<br />

( ( ( ( Z ) ) , HSf<br />

O ) QN )<br />

~<br />

ϕ ϕ ϕ<br />

+ ϕ<br />

Q<br />

3.12-4<br />

ZOH<br />

AA<br />

Equation 3.12-3<br />

The analogue measurements are converted into digital form using a 100 Hz,<br />

4 th order Butterworth filter, and a 12 bit ADC subject to 3 bits of noise and a<br />

sampling rate and range matched to the output interface.<br />

3.12.5 Sensor Limitations<br />

The provision of HMS measurements at the output interface depends on:<br />

• User measurement selection ( MS_MSAV2 bit 15/16 cleared )<br />

• Maximum range limiting ( GB_HS_ER bit 15 is set )<br />

• Angular rate limiting ( GB_HS_ER bit 16 is set )<br />

• Maximum angular rotation limiting ( GB_HS_ER bit 17 is set )<br />

When active, if any of these limitations are violated, bits 15 - 16 in the<br />

measurement ready flag MS_MSRY2 are cleared. Failure to provide a<br />

measurement at the user request is indicated by setting bit 0 of GB_HS_VF.<br />

If the target range exceeds 12 km, the segmentation capability of the human<br />

eye in blue-sky conditions, bit 1 of GB_HS_VF is set. When target LOS<br />

angular rate limiting is active measurement transmission is suspended and<br />

bits 2 - 3 of GB_HS_VF are set (rate limiting in elevation and bearing<br />

respectively). If the elevation or bearing angles exceeds (± 60°, ± 120°)<br />

bits 4 - 5 of GB_HS_VF are set respectively.<br />

3.12.6 Output Interface<br />

The measured target angles pass through a signed 16 bit digital interface at a<br />

frequency (HSfO) of 50 Hz (clock 14). They are subject to bearing and<br />

elevation interface range limits of ± 180° and ± 90° respectively, and a onecycle<br />

transmission delay.<br />

HS<br />

Z ~<br />

IF ⎛ IF ⎛ IF<br />

⎜<br />

⎛ IF<br />

= ϕ ϕ ⎜ ϕ ⎜ ϕ ⎜⎛<br />

D<br />

Z , HSf<br />

TD Q LIM<br />

O<br />

⎝ ⎝ ⎝ ZOH ⎝<br />

~<br />

:<br />

⎟⎞<br />

⎠<br />

⎞<br />

⎟<br />

⎠<br />

⎞<br />

⎟<br />

⎠<br />

⎞<br />

⎟<br />

⎠<br />

Equation 3.12-4

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