Odd Sensor Design

[Rich Grise]

On Tue, 18 Jan 2005 06:05:46 -0600, Richard wrote:

We have an engine model which is prone to a particular problem. When the
engine goes down after it fails a turbo charger, it slowly fills the
aftercooler and intake manifold up with oil. When the engine shutsdown, the
aftercooler drains the oil into the manifold. When a operator tries to
restart the engine, the cylinders fill up with oil (only after it actually
starts) then hydro locks and spits a connecting rod out the side of the
block. {yes, the engine generally starts fine with no hydrolock until it
starts coming up to speed, then it sucks the oil in and BAM!}

I've been following this thread rather closely; you've noticed I've asked
a couple of questions. So, I'm getting that when the seals fail, the sump
fills with oil, which isn't that much of a problem until they try to
restart. Feed pressure to the bearing itself isn't a good indicator,
because it isn't the bearing that fails, just the seal. And you want to
make it careless-operator-resistant.

A scavenger pump doesn't make much sense, because it isn't supposed to
happen routinely. So, how do you sense oil? Optics of some kind, I think.
Is there room in the sump for a stock optical interrupter?(-or?) I rather
like that idea of the probe with the wedge at the end, but have no idea
what the refractive index of oil is, or what it would do to the reflective
properties of the wedge. Interesting thought experiment, however.

In any case, Good Luck!
Rich

 

[Spehro Pefhany]

On 19 Jan 2005 14:34:38 -0800, the renowned bill.sloman@ieee.org
wrote:

Your Nichrome wires are doing the same job as thermistors, but with
much lower sensitivity to the temeprature differences you are trying to
detect. Thermocouples don't normally dissipate any power at all, so
they would be perfectly useless.

You don't need two sensors - if you measure the the self-heating of a
single sensor at two different current levels in quick succession (the
time constant of a bare thermistor is about a second) you've got all
the information you need.

Time constant in air of a thermistor can be pretty damn slow.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com