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
