calorimetric principle

[moctod]

Looking for circuitry to construct a simple "on-off" flow sensor based on the
calorimetric principle. Don't need to measure rate of flow but need to detect the presence or absence of flow. Know about inline mechanically driven or actuated devices but am looking for a reliable, relatively non intrusive way to monitor flow. Any Ideas?

 

[Paul111]

Hi, I'd like to help but you will need to be way more specific.
The definition of calorimetric is:
1. An apparatus for measuring the heat generated by a chemical reaction, change of state, or formation of a solution.
2. The part of this apparatus, usually a container for holding a sample, in which the heat measured causes a change of state.
Principle??
How does this relate to your project?

 

[j.p.bill]

It sounds like you want to put a thermistor into the fluid, and look at rate of heat loss as indicating flow. This can be tricky, as a self-heating thermistor will make its own flow in still conditions. It may be good for on-off sensing.

The interesting part is that any change in the fluid's temperature makes the thermistor behave differently. So, if it has a resistance of 10 ohms @ 20C, it will be significantly lower with the temperature up at 25C.

Getting this to work requires a bridge, with a compensating thermistor held at the fluid temperature, but not self heating. It's a real pain to try to work out.

 

[ericgibbs]

hi,

Is the medium your trying to detect the 'yes/no' flow for, a gas or fluid.?

Is the 'flow tube' material , clear glass, plastic etc. Whats the 'bore'

Regards

EricG

 

[moctod]

The flow to be detected is liquid, but could als be gas or air.
The device would consist of a probe with some sort of heating element. An additional probe or probably two probes would contain temperature sensitive elements that would have a voltage or a resistance that varies with the temperature of the liquid. As the liquid around the heater probe heats up the temperature is measured. Flow would create dispersion of the heated liquid therby reducing the temperature around the probes to something approximating the ambient temperature of the liquid. The sensor would detect the difference in temperature either between the the heater probe and the sensor probe or between two sensor probes and provide an output. It would probably be possible to determine the direction of flow also depending on the alignment of the sensor probes.

 

[Roff]

Here's a patent that uses this principle.

 

[moctod]

Here's a patent that uses this principle.

Darn! Thanks! Will investigate.

 

[Hero999]

If it's patented and you use it can't you be sued?

Or is it alright providing you don't sell it?

 

[Roff]

If it's patented and you use it can't you be sued?

Or is it alright providing you don't sell it?

Here is a discussion of Patents and Personal Use. Within this is a portion of U.S. patent code, which says that personal use without permission is infringement, except "for the sole purpose of gratifying a philosophical taste, or curiosity, or
for mere amusement".
If you read on down it points out than an individual infringer is unlikely to be sued (at least in U.S. courts) because of the expense involved. Patent law and the party responsible for litigation costs may be different in other countries.

 

[Hero999]

I don't know where I stand on patents, half of me thinks they hold back technology but the other half thinks they provide financial incentives for innovation.

 

[Roff]

I don't know where I stand on patents, half of me thinks they hold back technology but the other half thinks they provide financial incentives for innovation.

Well, from a strictly selfish point of view, they're great! In the 10 years that I have been with my current employer, I have been granted 31 patents, and each earned me $2000 when filed, and another $1000 when granted. That averages out to over $9000/year in additional personal income.
I think my employer values patents by the pound. I believe they are mostly used for technology swaps, and for leverage in patent disputes.