LAOS Laser

I think it's a good idea. Note that this specific flow sensor has 1/2" thread and the laser coolant tubes are significantly smaller.

Another option: a flow switch: http://nl.rs-online.com/web/p/flow-controllers/0257076/
This switch can be incorporated in the safety system. You could even wire it in series with the lid interlock switch.

Here in Fablab Amersfoort we use these for our lasercutters. No problems so far.
http://nl.farnell.com/jsp/search/productdetail.jsp?SKU=1734677

I removed a flow sensor from a scrap household espresso machine. It gives pulses that I have connected to a tiny beeper so I can hear the water flowing while I am testing. I will add a missing pulse detector to it to drop a relay if flow stops and cut the laser safety loop.

It seems very well made but I have only seen one price of EUR60 which seems high, though I have not been looking, perhaps available as a machine spare part for less.

I also found a blog showing another user investigating the same or very similar sensor to the one I have.

http://www.digmesa.com/en/classicline-products/flow-sensor-fhksc/
http://www.pcbheaven.com/exppages/Experimenting_with_Liquid_Flow_Sensor/

Kalle
--
Johannesburg, South Africa

Found source for the small flow sensors units for espresso machines. Prices vary from US$10 to US$45.
They are small enough to fit into the machine, some have a small grit filter inline.

The small Digmesa units are rated from a max flow rate of 400 to 1200 ml/minute The largest one has a 2mm orifice and should be enough for most 40W lasers I expect (I will drill mine to 2mm when I get a better pump). It looks like many of the coffee machine units have the 1.2mm orifice but I think with a slightly bigger orifice up to the inlet hose barb internal diameter they should work well up to flows required for 150W (Reci says 2 to 5 litres per minute) tubes with reasonable pressure drop/flow restriction.

The data sheet for the small Digmesa unit does not say but some of their other units indicate a voltage range that includes 5V. If it was plugged into the analogue input of the LAOS board with a bigger resistor and capacitor it would smooth out the slow 1 to 10Hz square wave to somewhere around 2.5V when there are pulses. With no flow it will read close to 5V or 0V so could work as a pretty good watchdog circuit with very few extra parts. With no filtering (like the analogue output pin) the pulses could be counted and the LCD could show the exact flowrate. The analogue input could be used to measure the voltage across a PTC thermistor and give a display of the (tube outlet) water temperature. Which could indicate a need to add ice bricks or invest in a bigger chiller.

http://www.nelsonappliance.com/Krups_Espresso_Flow_Meter_MS_0A01717_p/krms0a01717.htm US$10 looks like a Digmesa unit
http://www.nelsonappliance.com/Krups_Espresso_Flow_Meter_MS_620748_for_XP2070_p/krms620748.htm US$15 similar unit with filter
http://www.seeedstudio.com/depot/g14-water-flow-sensor-p-1345.html US$9.50 similar unit larger hose fittings, larger flow range
http://www.shop.partsguru.com/Flowmeters_c563.htm US$45 A number of units including larger commercial ones

Kalle
--
Johannesburg, South Africa

Why not just add a temperature sensor at the tube?
Should be a lot cheaper.
Not sure where excatly to put the sensor, though.

Andreas
Munich, Germany