Paul  wrote, quoting Tracy Crooke:

Data sent in following order:   (10 bit values are sent as 2 bytes,

LSB

first, right justified)

Start Flag  (8 bits)  F0 hex  Indicates start of data group.

1.    O2 sensor output.  fuel/air mixture (10 bits)  255 = stoic.

mixture.

      higher = richer
2.    MAP  manifold pressure (10 bits)  841 = 30" Hg. , 200 = 10" Hg.
3.    Air temp (engine inlet ait temp) (10 bits)  511 = 25 degrees C.

(curve

      not defined yet)
4.    PGM  current setting of programming knob. (10 bit) 0 - 1023)
5.    Mixture current setting of mixture knob  0 - 1023
6.    Fuel Flow (10 bit) 0 - 511    511 = approx 20 GPH on 13B, 30 GPH

on

      20B
7.    Table data in use.  (10 bit) Current mixture correction table

entry.

8.    engine speed (10 bit) (1 mhz clocks during 30 degrees of

crankshaft

      rotation)
9.    Table address  (8 bit) 0 - 63  Address of current table entry in

use.

10.    Staging flag (8 bit) 0 or 1,  If 1 then fuel flow must be

divided by

       2 (one injector per rotor in use)
11.    EOX  end of message byte (8 bit) F7 hex

Russell Kent wrote:

Paul or Tracy,
Item 8 (engine speed) works out to a *minimum* measured engine speed of

about 4,887

RPM.  That seems like a very high threshold.  The upper end of the

measurement window

is 5,000,000 RPM.  Perhaps it doesn't matter, but one can lower useful

range by

either adding a few significant bits (each one halves the minimum

measured RPM) or

putting a "divide-by" circuit in the 1 MHz pulse chain.

Also, perhaps item 6 (fuel flow) should be re-labelled "fuel injector

duty cycle".

This would help clarify (to me, at least) what's being reported so that

item 10

(staging flag) makes a bit more sense.  Then fuel flow becomes: 20 *

duty cycle /

(511 * (staging +1)) GPH.

Russell Kent

Tracy Crook wrote:

On #8,  The number of bits is wrong.   It should have read 16 bits.

On #6,   It's OK with me to think about it as duty cycle :-)   Note that the
fuel flow instrument I am developing will have a correction table to
calibrate this non linear value. (the correction table is for the
microprocessor so the pilot doesn't need one :-)

Tracy Crook
rws@altavista.net
www.rotaryaviation.com

 
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