motion sensor

Thread Starter

woodguy60

Joined Sep 21, 2011
20
I own a cnc woodworking machine that use a water cool spindle[motor]
what i am looking for is some type of motion detecting to bring on a light or alarm
if the water stops flowing.
the water flows in a transparent 3/8 plastic tube.
there is also a plastic flow indicator in the line that spins when the water is flowing
so i was thinking maybe a sensor that will turn on if the plastic indicator
stops moving.
thanks paul
 

MrChips

Joined Oct 2, 2009
20,911
I would try an LED and photo sensor that detects the motion of the flow indicator. The signal from the sensor triggers a retriggerable monostable multivibrator that is set with a time constant that is longer than the expected period of the flow sensor. When the flow sensor is spinning properly the output of the monostable will remain high. When the flow is stopped the output will drop low.
 

Thread Starter

woodguy60

Joined Sep 21, 2011
20
sound good . any idea where i can find a circuit for this?
i am not very good at electronics
need something simple
thanks paul
 

MrChips

Joined Oct 2, 2009
20,911
I will see what I can do with a simple 555 circuit. You will have to do some experimenting with the photo sensor portion.
Would you be able to post a closeup photo of the flow indicator?
 

BMorse

Joined Sep 26, 2009
2,675

If it is going to be mounted on the CNC, then no, the vibrations from the machine alone will think the water is running even if it was not......

Do you add any cutting fluid to the water??? if so, how dark is the color? if the water was slightly colored than the plastic tubing, then using an IR or visible LED and a photosensor may just work, since the light passing thru the clear tube will be more visible to the sensor than if the "colored" water was passing through.... just a thought.... here is a simple LED Phototransistor hook up, replace the 10K resistor with a 1K and a potentiometer in series to vary the "trigger" treshold....


here is another circuit using a comparator with variable gain adjustment


and here is one that may work with a Red LED as the light source....
 
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Thread Starter

woodguy60

Joined Sep 21, 2011
20
the water supply tank is mounted on a brick wall with a submersible pump
the antifreeze is green but looks very dark in the tube.
i believe over time it has discoloured the tube.
as it still remain the same original colour in the tank.
thanks paul
 

BMorse

Joined Sep 26, 2009
2,675
Probably looks just like my water lines for my lathe and mill :).... I will throw something together out of parts that should not be that hard to come by,.... by the way, what exactly do you want the "sensor" to do once it "sees" that there is no water flow, just sound a buzzer, light an LED or both? We could probably include both just for the sake of it :)
 

BMorse

Joined Sep 26, 2009
2,675
now, you also said water cooled spindle...... so there is a return line on the spindle back to the tank? If so, the sensor should probably be placed on that side of the cooling lines, just in case it clogs up along the line and does not flow all the way back through, so it could serve a dual purpose, no water, and clogged line detector :), just another thought.........
 

MrChips

Joined Oct 2, 2009
20,911
Here is an experimental circuit.



I used whatever transistors and components I had laying around. You can substitute your own.

LED D3 and photo transistor Q1 should be replaced with infra-red LED and detector to prevent interference from ambient lighting.

You can have the LED shine on the flow indicator and have the photo-detector pick up the reflected signal or you can use a transmission mode shining through the flow indicator. Just experiment with it. You may also have to play around with the gain or sensitivity. Having an oscilloscope would be handy.

That is why an off-the-shelf flow sensor would make the project fairly simple and straight forward.

For simplicity, I have shown two status LEDs, one GREEN and the other RED. You could replace this arrangement with an audible buzzer.
 

Thread Starter

woodguy60

Joined Sep 21, 2011
20
B Morse using the return line make alot of sense
thanks for the circuit MrChips.
i have to give this some more thought and if i find its getting to difficult
for me to carry out.
i will go to the suggestion with an off-the-shelf flow sensor.
i realy appreciate the time you both are taking to help.
also not sure if i can gets the parts for the circuit where i live Barbados

paul
 

Thread Starter

woodguy60

Joined Sep 21, 2011
20
i am now in the UK on vacation back to barbados on sat.
<SNIP>
and back to work.
paul
 
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strantor

Joined Oct 3, 2010
5,226
Hey, get a metal enclosed metal tank and hang it from a spring. run your hose into the top and another coming out the bottom to your lathe. put a metal rod above the tank just far enough up so that when the tank is full it won't touch the rod, and when its half full, it will touch the rod. connect one wire to the bucket and one to the rod, so it will go like: battery + ->tank.... rod->alarm/light->battery-. Bingo, alarm, and the kicker is it goes off before you lose all your cooling fluid (gravity drain)
 

THE_RB

Joined Feb 11, 2008
5,438
Maybe I'm missing something, but I would just use a temperature sensor? That is the actual problem you need to be warned about, which incidentally happens to be easier and more reliable to test. If the water fails in any way the temperature sensor will let you know within a few seconds.
 
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