Quote:
Originally posted by Gooserider
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.
|
You're right...
Quote:
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.
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 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
|
So it seems that RPM is done purely magnetical, not by hall effect.
The 7812CT is a TO220 12V-1A max voltage regulator.
The 2N3904 is a small signal NPN transistor, probably for buffering the opamp output signal and triggering the relay.
The CA3140 is a mosfet opamp and probably works as a comparator between a fixed (user settable) DC level and the integrated pulses from the sensor.
Best thing to do is to try to reconstitute the schematic following all the traces and components on the circuitry and drawing it down on a piece of paper, and then try to understand it (with the help of the datasheets of the components).
I suspect a usable RPM signal (AC pulses from the sensor) to be available just before the opamp, and before the integrator (which is probably just a (rectifier) diode, a serial resistor and a parallel cap).
All you should have to do with the AC pulses is rectify them with a diode, put them through a schmitt trigger to obtain clean square wave pulses, and then feed them to an open collector transistor.
Ofcourse a scope (even // port based or LCD based) would be usefull.
CD
