On Tue, Nov 5, 2013, at 11:20 AM, Michael Haberler wrote:
>
> Am 05.11.2013 um 16:27 schrieb andy pugh <[email protected]>:
> > One issue is that the NIST design is very specific that only one thing
> > can ever change another thing, ("NIST logic") and you are proposing to
> > change that. I am not sure that is a bad thing (and could be a very
> > useful thing) but I would like to understand the logic behind the NIST
> > policy.
>
> Nobody _forces_ you to associate two buttons with an output pin just because
> the protocol supports this, and it would not have made sense to design things
> differently in view of this consideration. But I would think in process
> control several monitors of a single process is a standard use case. Again,
> this is not possible today but will become possible.
>
> How does your reference to "NIST Logic" add up with the fact that we can run
> several NML-based UI's in parallel today? and how would that be different to
> this proposal?
>
> could it be that this is just some major misunderstanding what this is about?
>
> -m
My understanding of "NIST logic" is a bit different. It is harder to put it
into precise words than it is to give an example:
The example - suppose we are talking about a simple on-off variable like
"machine on" or "drawbar unclamp". The non-NIST approach would be
to put a toggle switch on the panel, and label the two positions as ON and
OFF. But what happens when you want to control it from two locations?
If you have two toggle switches, and one is ON while the other is OFF, the
result is undefined or confusing.
The NIST approach would be to have two buttons labeled ON and OFF,
and a light, at each control location. Pressing either ON button would turn
the function on and light the light. Pressing either OFF button turns it off
and extinguishes the light. Both operator stations can see the current state
of whatever it is they are controlling, and since the buttons don't have "state"
of their own, the control device state is never out of sync with the actual
signal state.
The same applies to analog values - suppose we are talking about feed
override (or some other 0-100% variable). The non-NIST approach might
be to put a knob on the control panel with a 0-100% scale around it. This
becomes a problem if you want to control the same value from two or
more places. If one knob is set at 50% and one is set at 75%, which one
wins?
The NIST approach would be to put a bar graph or numerical or such
display of the current value at each control location. And each location
has UP and DOWN buttons, or perhaps a knob (with no scale on it)
connected to an encoder. Pushing the buttons or turning the knob would
change the value, the current value can be seen at each location, and you
never have a dial indicating the wrong value.
John
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