Post by thread:Flow sensing

'Flow sensing'

>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.

--

http://www.piclist.com hint: The list server can filter out subtopics

(like ads or off topics) for you. See http://www.piclist.com/#topics

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}> >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.

>

> --

> http://www.piclist.com hint: The list server can filter out subtopics

> (like ads or off topics) for you. See http://www.piclist.com/#topics

>

--

http://www.piclist.com hint: The list server can filter out subtopics

(like ads or off topics) for you. See http://www.piclist.com/#topics

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}
>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?

--

http://www.piclist.com hint: The list server can filter out subtopics

(like ads or off topics) for you. See http://www.piclist.com/#topics

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

--

http://www.piclist.com hint: The list server can filter out subtopics

(like ads or off topics) for you. See http://www.piclist.com/#topics

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

--

http://www.piclist.com hint: The list server can filter out subtopics

(like ads or off topics) for you. See http://www.piclist.com/#topics

> 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

--

http://www.piclist.com hint: The list server can filter out subtopics

(like ads or off topics) for you. See http://www.piclist.com/#topics

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]

--

http://www.piclist.com hint: The PICList is archived three different

ways.  See http://www.piclist.com/#archives for details.

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}> >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?

>

> --

> http://www.piclist.com hint: The list server can filter out subtopics

> (like ads or off topics) for you. See http://www.piclist.com/#topics

>

--

http://www.piclist.com hint: The PICList is archived three different

ways.  See http://www.piclist.com/#archives for details.

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

--

http://www.piclist.com#nomail Going offline? Don't AutoReply us!

email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

>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.

--

http://www.piclist.com hint: To leave the PICList

.....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

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

_______________________________________________

http://www.piclist.com

View/change your membership options at

http://mailman.mit.edu/mailman/listinfo/piclist