Digital pianos are now trying to incorporate a similar improvement, and I'll post here a PDF I've clipped from some CASIO brochure (which since it's infoblurb shouldn't matter) as PRIVIA ACTION.

The graph is interesting, seems to imply that on the (uncircled) return-crosses of the Sensor 2 level, a note-off will be sent, to match the previous (circled) note-on message. But also implied is that until full key-release is achieved (blue circle) the damper will not be fully-dropped and all sustained sound cease. Further implied is that this action provides for repeated presses to start from different key-depths, allowing for greater velocities to be achieved, as well as lesser ones, on the re-strike. Overall could be a problem for fast staccato (and real grands may have this too), plus may be different from other systems (in particular KAWAI's, where the sensors are hidden from inspection, so who can know).

I don't know what zooming particular PDF readers provide (I use NITRO), but at worst, open it in Adobe Reader and there'll be zooming. Switch attention to the Action diagram - 400% and a bit of thought taking count of the graph will show how the action works.

In particular note how very close are the actuating positions of sensors 2 and 3, compared to the relatively enormous gap to key-release (damper ON). Close = fast!

No idea how aftertouch is implemented, and it's too new to have any settled industry approach, but polyphonic aftertouch is almost bound to be expensive.

ADDED: PDF isn't a file type that can be posted here, so I'll stick PRIVIA ACTION.PDF in my DropBox, and here's the LINK.

Some of my favorite trumped up specifications include the use of "ivorite" and "ebonite" or some similar name to imply the feel of ivory in a keyboard.  The irony of this is that ivory has been essentially discontinued and replaced by plastic key coverings, even in the finest real grand pianos manufactured since the early 1950s.

My own preference for keyboards include those made with wooden keys with plastic key covers, instead of purely plastic keys.  The latter have a tendency to deflect sideways, and have a "cheap" feel to them.  I also get the feeling that purely plastic black note keys have the capacity of being sheared off, if one were to perform a hard black key glissando on them.

* * * * * *

In the end, my suggestion is for you to buy the best quality keyboard you can afford, even if that means spending more money than you had initially intended.  If you buy a cheap keyboard, you will be unsatisfied with it in very short order.  Conversely, if you buy a more expensive, but substantial keyboard, you will be happy with it for years to come.

I happen to own an ancient Roland A-80 mother controller keyboard, purchased new in 1990.  Other keyboards have come and gone from the market place, but I have never felt the need to "trade up", despite advertisements for graded hammer action, various escapement emulations, ivorite keyboards, etc., etc.

Cheers,

Joe

People today buy too much from internet by just looking specifications, without test the product.

My advice is to go to a music store and play several brands of keyboard.

Do i really need to care 3 sensor keyboard?

If a 3 sensor keyboard is required then there are a lot of us out here who are in big trouble because I'm sure most of us only have 2. I won't try to say exactly what a 3 sensor board will do for you because I have not used them often but there may be some others here who will try to answer that question.

I am considering between
P155 Yamaha GH action 2 sensors.
FP 80 roland PHA iii ivory feel s with escapment. 3 sensors .
Rd700nx PHA iii ivory feel with escapment 3 sensors.  High price issue.

Do i really need to care 3 sensor keyboard?

Can anyone help me?

Thank you