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'Flow sensing'
2004\08\20@045230 by Alan B. Pearce

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>I got an offer for $840 which is hardly
>affordable for that project.

However, how much is this in relation to the laser equipment you are trying
to protect ?? It sounds rather like penny pinching to protect something
which is somewhat expensive.

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2004\08\20@063312 by dr. Imre Bartfai

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Hi,

you are right, But the question is not to protect the laser gun (the pump
runs anysay) but to protect the pump itself against running in unloaded
state.

Imre

On Fri, 20 Aug 2004, Alan B. Pearce wrote:

{Quote hidden}

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2004\08\20@073016 by Anand Dhuru

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I'd read abot a thermistor physically coupled to a heating device (as in a 1
watt resistor) being introduced into the pipe; the value of the thermistor
will change drastically with flow. In your case, since the water is already
heated, this differnce might be smaller, but still measurable.

Regards,

Anand Dhuru

{Original Message removed}

2004\08\20@101040 by Alan B. Pearce

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>you are right, But the question is not to protect the
>laser gun (the pump runs anysay) but to protect the
>pump itself against running in unloaded state.

That is a situation that would be more worrying to me. For the pump to run
in unloaded state, there must be no water in the system. Surely the laser
has a protection against this.

If there is never a situation where there is no water in the system, how can
the pump be running unloaded?

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2004\08\20@134303 by Matt Pobursky

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On Fri, 20 Aug 2004 15:13:09 +0100, Alan B. Pearce wrote:
> > you are right, But the question is not to protect the laser gun
> > (the pump runs anysay) but to protect the pump itself against
> > running in unloaded state.
>
> That is a situation that would be more worrying to me. For the pump
> to run in unloaded state, there must be no water in the system.
> Surely the laser has a protection against this.
>
> If there is never a situation where there is no water in the system,
> how can the pump be running unloaded?

One situation would be a coolant line break. Depending on the thermal
dynamics and overall flow rates of the system that could result in a
catastrophe pretty quickly.

The flowmeter I posted the link to is typically used in the plastics
molding industry to monitor the coolant flow and temperature in a
molding machine. It protects the mold itself by monitoring the coolant
flow through the cooling jacket of the mold. By monitoring the
temperature and flow rate on the inlet and outlet side of the mold, you
can get a pretty accurate reading on the cooling system performance.
The molding process adds many 10,000's, if not 100,000's of BTUs to the
mold and if not cooled can warp and crack the mold cavity details or
cooling ports. Since the molds can be worth $100,000+ (and quite
frequently are) a loss of cooling for any significant time can be quite
expensive! Occasionally a cooling hose will break or fitting fail and
the coolant flow is interrupted, thus the need to monitor it and shut
things down in a timely and orderly fashion if that happens.

Matt Pobursky
Maximum Performance Systems

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2004\08\20@135134 by Matt Pobursky

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On Fri, 20 Aug 2004 15:13:09 +0100, Alan B. Pearce wrote:
> If there is never a situation where there is no water in the system,
> how can the pump be running unloaded?

One other thing I meant to mention...

An old engineer once told me "Good design really shows up not when
things go right, but when things go wrong".

Maybe it's just the industries I typically design for (high reliability
industrial controls and medical electronics) but I find as much of my
design work goes into asking "but what if... ?" questions and providing
graceful failure modes as goes into the actual normal product operation
itself.

It's something I seem to see less and less of in designs I review as
time goes by and it's kind of scary.

Matt Pobursky
Maximum Performance Systems

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2004\08\20@232028 by Gerhard Fiedler

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> I'd read abot a thermistor physically coupled to a heating device (as in a 1
> watt resistor) being introduced into the pipe; the value of the thermistor
> will change drastically with flow. In your case, since the water is already
> heated, this differnce might be smaller, but still measurable.

That can be made even easier by driving a current through the thermistor
that's high enough to heat it without water running. Depending on the speed
of the normally running water, the cooling effect can be quite dramatic.
(There is that other thread about potting temperature sensors... :)

Gerhard

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2004\08\21@001808 by Peter van Hoof

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The high pressure differential over the load you mention and the low flow
would make me put a bypass ( a regulated leak) around the laser this way you
would always have some flow and the pump would not start and stop as often .

[snip]
> the question is not to protect the laser gun (the pump runs anysay)
> but to protect the pump itself against running in unloaded state.
[snip]

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2004\08\21@110938 by dr. Imre Bartfai

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Hi,

they told me in this case (maybe the correct expression instead of
"unloaded" is "without payload") the cooling of the pump itself will be
insufficient and the bearing of the pump becomes hot and therefore
damaged. This is what they want to avoid.

Imre


On Fri, 20 Aug 2004, Alan B. Pearce wrote:

{Quote hidden}

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2004\08\22@102034 by Howard Winter
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Matt,

On Fri, 20 Aug 2004 12:51:10 -0500, Matt Pobursky wrote:

>...<
> An old engineer once told me "Good design really shows up not when
> things go right, but when things go wrong".

I agree completely!

> Maybe it's just the industries I typically design for (high reliability
> industrial controls and medical electronics) but I find as much of my
> design work goes into asking "but what if... ?" questions and providing
> graceful failure modes as goes into the actual normal product operation
> itself.

Unfortunately in the IT industry the common way to create a system is to get a specification from the User as
to what they want, do an outline design, get them to agree it, do a detailed design, get them to agree it,
then build and test it to the spec.  If it meets the spec, it is deemed to be finished.  Nowhere in here is
there a "Yes, but..." stage, which I have always advocated, but which a lot of others think is a Bad Thing!

You cannot rely on the user (or whoever takes that role, in the case of commercial products) to mention or
spot problems because they may have no experiance in such things.  It is up to the professional to look at the
design and try to spot the potential problems, and to design around them.  But it's rarely taught, and even
more rarely actioned, because time and money budgets are usually too tight.  This is where £1million
electricity bills come from!

> It's something I seem to see less and less of in designs I review as
> time goes by and it's kind of scary.

Indeed, and it frightens me in particular where safety-critical systems (Nuclear power stations, Fly-by-wire
aircraft controls, traffic lights, ABS systems etc) are concerned.  But it also applies to stock control,
invoicing, payroll, VCRs, alarm systems, and so on, where anomalies should be tested-for and reported, even if
it's not possible for the system to fix them itself.

Cheers,


Howard Winter
St.Albans, England

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2004\08\23@081257 by Alan B. Pearce

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>they told me in this case (maybe the correct expression
>instead of "unloaded" is "without payload")

Yeah, I can live with either expression as meaning the same thing in this
context.

>the cooling of the pump itself will be insufficient
>and the bearing of the pump becomes hot and therefore
>damaged. This is what they want to avoid.

OK, that explains a lot of things about "why" you want to do it.

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2004\08\28@111210 by dr. Imre Bartfai

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Hi PIClisters,

thank you all for contributions. After looking some of home pages you told
I found a pointer to an European site (http://www.profimess.de) which offer an
appropriate flow sensor, adjustable, for EUR160+delivery. I prefer
European supplier due to customs & tax constraints (my country, Hungary
became member of EU by 1st May, so all deliveries count as inland).

I will report the final solution if there is any interest.

Thank you again for all valuable contributions.

Regards,
Imre


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