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Turbokeu: I don't want to dissapoint you but I had a look at the 0100B110 datasheet on Proteus Industries's website: 1) It's a flow switch with user settable trip point, not a flowmeter, so no way to do RPM monitoring.
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That is the official line. However, they do make a similiar model that DOES offer flow monitoring, as well as the switch. I know that it is very common as a cost saving measure to use the same circuit board for all models in a product line, and just not implement all the features.
The circuit board in this unit is almost fully populated, the only spaces left on it are for a resistor, a large transistor, and a relay (looks like they intended to have a second alarm for excess flow perhaps?)
There is also a two pin connector, which isn't documented, near the other connections to the unit. Makes one go Hmmmm....
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2) Output is a 120VAC-3A max SPDT relay contact.
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Looks about right. I figure I can use it to trip a larger relay that would trigger an alarm and/or shut off the PC and pump power supplies.
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3) Pipe connections are only 1/4" NPT, pressure drop is 6psi!
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True, but I don't think that will be a problem. I am going to be doing multiple parallel cooling loops and the loop this unit was going on won't need much flow, indeed it will help prevent the loop from getting excessive flow. My pump has a 14' head rating, so it should be able to handle it. I suspect that may also be a 'worst case' pressure loss value, the unit's block has 4 ports, two are used, and two are plugged, but which ones depends on the desired range of flow rates. I suspect the higher ranges will be less restrictive.
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4) Flow speed is indicated visually by rotor speed.
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True, but the only way the rotor can be sending info to trip the relay is if it's sending some sort of pulse to the circuit board. I have difficulty believing there wouldn't be some way to tap into that pulse and get a tach signal from it.
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There is another possibilty if you have some serious electronic skills: Dismount the electronic circuitry to analyse the actual schematic. I suspect the rotor to be a sort of a hall effect generator with magnets. Create your own schematic using the hall generator's signal to output an open collector signal proportional to the flow speed and suitable for RPM monitoring.
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Well, I want both functions, so I want to keep this board around. So far this is what my investigations have found:
The rotor is magnetic, there are magnets embedded in 3 of the 6 arms.
The block appears to be stainless, with the rotor chamber machined into it. The only openings in the champer are the front faceplate, and the 4 pipe entrances. The back side has a well machined into it that just misses the chamber, and contains the sensor.
The sensor appears to be an inductor, it's about 3/16" (5mm) dia. by about 3/4" (19mm) long, positioned such that the tips of the rotors probably sweep by it. It is the only component on a sensor board, which is secured in the well by two nylon screws. There are two wires from the sensor board to the main module, which can optionally be located a good way from the block.
The main board has only 3 active components on it, along with a small handful of diodes, caps, resistors, etc. One component is a Motorola 7812CT regulator. (marked VR1) There is also a 3904 transistor, and what appears to be the 'brains' of the unit; an 8 pin chip, I'm not sure of the make, labeled CA3140EX.
I haven't chased down the function of this chip yet, but I suspect it functions to integrate the pulses put out by the sensor and control the relay triggering.
Gooserider