160624-1523 EDT
jbonest:
First, you need to understand how various electrical components work. An understanding of what may be inside of this "black box" is next. This is going to be a guess without opening the device. Any specific written information on how the device works is quite important.
From the information you have provided this appears to be a liquid level control, and of a single point type. That would imply an on-off operation at a single point. What is supposed to be the theory of operation relative to detecting water or some other liquid. Is this a conductive, capacitive, inductive, optical, thermal or other type of liquid level sensor? My guess is it is a conductive sensor. Can it detect distilled water, or oil?
You need to know its theory of operation. Does it use a DC or AC voltage for sensing? Is this sensing voltage isolated from the AC power source? What is the sensing voltage magnitude? Over what resistance range is the sensing threshold adjustable?
From the information you have provided we can guess that there is internally at least a transformer, and an electromechanical SPDT relay. This relay has two states. We assume the the relay marking means that the NC contact is closed when there is no liquid contact, and thus a pump motor should run under these conditions. If this contact is also closed when no input AC power is applied, then this is not a fail safe design. However, deriving input power to the relay contact from the same source as the input to the control does make it fail safe.
I would use the ohmmeter function of your meter to check for continuity from each of the AC input terminals (L and N) to the relay COM terminal. Obviously done with no input AC power. From your measurements I assume a relatively high resistance. Probably above 1 megohm.
With no input AC power applied is COM to NC open or closed? With your probe in free state does COM to NC change state whren AC input power is applied? If it changes state, then at least part of your control works.
You need to know what the maximum probe voltage is and if you touch the probe can you get hurt. What two terminals define the probe circuit? One is the probe, I have to assume the other is the ground terminal. With power input present short the probe to the ground terminal. You should hear a mechanical click inside the "black box". I am assuming an electromechanical relay as the output for cost and because it is SPDT. As well as hearing a click you should see continuity change across the terminals COM to NC.
Doing these tests on a bench is the best way to study the device.
Provide more information.
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