Altittude knobs A320
Joined: Jun 2007
Posts: 3,443
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From: Wanderlust
FE Hoppy
Sure!
Are the knobs single rate or dual rate?
If dual I hope you know the rate required to change from fine to course adjustment!
If dual I hope you know the rate required to change from fine to course adjustment!
V/S or FPA knob Range (V/S) : –6 000 to +6 000 ft/min 2 clicks = 100 ft/min If the flight crew turns the knob slowly, each click equals 100 ft/min.
Joined: Jan 2011
Posts: 780
Likes: 89
From: Seattle
Most probably a binary (power of two) thing. Unless the knob has a physical scale and pointer, who would notice that 360 degrees isn't exactly one turn (at one degree per click).
Spinal Tap reference?
On the A330 it has 33 clicks a turn
Joined: May 2010
Posts: 443
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From: Boston
While back I did some work for a company where it was faster to change the HW (fpga) than the SW when a simple offset error was found.
Does the 33rd click get you back to starting point, if so so might call it 32 clicks.
Wonder if the 'testing' of click counts has produce any noticeable track deviations yet
Joined: Jan 2011
Posts: 780
Likes: 89
From: Seattle
who would notice that 360 degrees isn't exactly one turn (at one degree per click).
One click per degree makes sense because that's a logical increment for changing a heading. Need to change by three degrees? Three clicks. But the reference for the absolute heading would be a readout. Not the knob position. One could get one click per degree and one knob turn for 360 degrees of heading. But then the angular size of a click would be pretty small and difficult to set precisely by hand.
Back in the analog days, it was common practice to have a dial indicator concentric with a knob. But to gear the knob so that one degree of indicated change would take 10 degrees or so of knob rotation, making precise settings easier to accomplish. But the gear ratio between knob and dial wasn't exact (in some cases a friction drive).
When we went to digital controls, separating the display and knob functions, it made sense to add detents to the knob for touch feedback. So, one degree per click and let the software keep track of the absolute setting. The click size can then be anything that gives precise and easy control.
There are two ways of implementing a digital knob: A position encoder, that actually reads the knob position, multiplies it by some ratio and keeps track of the number of turns in software. Or, more simply, a knob that produces a single pulse plus a direction of rotation signal, letting the software increment/decrement the absolute value. This is much like a computer mouse, which has no idea where it is but sends the system up/down, left/right pulses and lets the software calculate from that. The latter is much easier to implement. A dual rate knob would simply check the rotation speed (clicks per second) and increment/decrement at a faster rate. All done in software.
Joined: May 2010
Posts: 443
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From: Boston
This is much like a computer mouse, which has no idea where it is but sends the system up/down, left/right pulses and lets the software calculate from that. The latter is much easier to implement. A dual rate knob would simply check the rotation speed (clicks per second) and increment/decrement at a faster rate. All done in software.
Joined: Nov 1999
Aviation Qualifications: ATPL
Posts: 3,150
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From: UK
Wonder if the 'testing' of click counts has produce any noticeable track deviations yet
*Apart from the altitude display which is always active and does not blank.
** Apart from the altitude knob which will change the altitude pre-selected, but the aircraft will not react until the knob is pushed or pulled.
Joined: Oct 1999
Posts: 668
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From: Adelaide
It was a dark and stormy night. Nothing on the instruments but the maker's name. Given that Aviators are a most curious bird, by their very nature, I'd have thought everyone secretly harboured a "need to know", just so you did.
