Am Samstag, 28. Februar 2004 02:21 schrieben Sie:
> At 04:00 PM 2/27/2004 -0800, you wrote:
> >Hi all,
> >
> >I have a project where a vacuum pump outputs a 22V signal indicating
> >whether it is working or not.  If it malfunctions (0V) I need to stop the
> >process.  The signal goes into a datalogger which is controlling
> > everything (I wasn't allowed to use a PIC to set this up).  The
> > datalogger needs a 5V signal, but I would like the pump to be
> > electrically isolated because it's very expensive and a huge pain to
> > fix/replace.  The way I decided to do this (one-time project) was use a
> > 24V-5V DC/DC converter (DCP022405P).  I have a 2.2k resistor that goes
> > from the converter's output to the digital input (it only tolerates very
> > low current) and also a 500 ohm resistor that goes from the output to a
> > LED for monitoring the status.  The inputs of the DC/DC converter come
> > straight from the vacuum pump (the pump signal is current limited to
> > about 50 mA).
> >
> >This worked great for about a month until someone unplugged the
> > connections to move the setup around.  Then it wouldn't work -- somehow
> > the chip just died.  I popped in another chip and it worked fine until
> > the power went out last night.  When the power came back on the chip was
> > fried again, no unplugging of anything.  I figured maybe some ESD the
> > first time, but now I'm not sure, maybe the pump output goes screwy at
> > times (it really shouldn't though).  Is there something I should be
> > putting in between the pump output and the DC/DC converter input to
> > protect it?  Some kind of resistor or RC combo?
>

A resistor for current limiting in serial and a 5V zener diode in parallel
should do the whole Job of the DC/DC Converter!!

Try to measure the behavior of the 22V output during the switch on and off
phase! May be there is a voltage peak during on and off switching.
For example, if the pump uses a coil to produce the signal current, than a
voltage peak is prescribed by the law of physics (during switch off, where
the magnetic field of the coil collapses and produces a very high voltage.

MfG,

Do.Pe.

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