Steve,
Linearity is only defined over the range 1kHz to 10khz, see note 5 in
the spec sheet. For practical purposes it extends from about 200Hz
to 12 - 13kHz, the bottom end depends on the filter capacitor. I am
retired now and without the necessary test equipment I can't do full
tests, but from empirical tests the response falls very rapidly, e.g.
@4.25kHz Vout= 2.5 @8.5kHz Vout=5, @12.75kHz Vout=7V & @17.5kHz Vout=
7.3V.
I will post a hand drawn circuit of my revised circuit later to-day.
Bernard
--- In mach1mach2cnc@..., Steve Blackmore <steve@p...>
wrote:
On Thu, 07 Aug 2003 00:36:53 -0000, you wrote:
Hi All,
A warning to anyone using a LM2907/2917 Frequency to Voltage
converter for spindle control. The chip data sheet does not
specify
an upper frequency limit, I have found that it is very non linear
above about 13KHz, I did not realize the problem with Mach1
because I
was using a D-FF as a pre-divider, however when I set up Mach2 for
a
Kernel speed of 35KHz I found that at above half spindle speed I
was
getting very strange results. The answer was to use the second D-
FF
on the chip, so there is now a divide by 4 pre-scalar to the
FtoV.
This modification should be good for M2 up to a Kernel frequency
of
45KHz.
Bernard - Can you explain this a little more, a circuit diagram
might
help? The National spec sheet shows it as pretty linear ie less than
0.4% across a 500kHz input range??
--
Steve Blackmore
