Experimental Physics and
Industrial Control System

Kurt Goetze <[email protected]> · Thu, 26 Jun 2008 11:34:56 -0500

Hi,
I have done something similar to what Bob suggests, in order to have

a BI record (set to I/O Intr) trigger something else after a delay. With

sysClkRateSet(2000) set in my st.cmd file, I was able to set delays

with a resolution of 1msec. Jitter was surprisingly good, a few % of a
msec,

iirc. The setup was VxWorks / MVME5100, in a crate with lots of other
stuff.

The binary input was an IP-Unidig input.
I experimented with higher clock rates but 2000 seemed to be the cutoff
for high resolution coupled with reasonable jitter, on my setup.
One thing I wanted to point out is that any old (in my case SNL) code using

vxWorks taskDelays will be affected by this. Obviously your delays will
get

much shorter with a faster clock rate! I found this out the hard way.
Another

reason taskDelay() calls should be converted to epicsThreadSleep().
Kurt Goetze
Dalesio, Leo wrote:

If you have the OS tick rate at 1 K Hz,
You could set the BO's HIGH field to something .001 - 1 millisecond
set the SCAN rate to .01 Hz
It is unclear what the jitter would be on the scan task - it should be under 100 usecs if you are on vxWorks or RTEMS.
Does jitter matter or just the pulse rate?
How wide of a pulse is required?
It would be interesting to hear your results.
Bob

-----Original Message-----

From: [email protected] on behalf of David Dudley

Sent: Wed 6/25/2008 9:54 PM

To: [email protected]

Subject: Pulse Train Record

Is it possible to use a bo for a pulse train output? I have an

application where I need to pulse a chemical metering pump which

requires a pulse train to control it at between 0-100 pulses per second,

and was wondering if I could use a simple digital output bit to do it,

or if I need some device support as well.
David Dudley
City of Corpus Christi

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System