Water with a circuit

I am more of a programmer than the actual electrical engineering side, so this may be a silly question, but if you are dealing with a device, such as a strain gauge, where you have two separate soldered points on the device, and you submerge that device in water, what can you expect to see happen to the output signal and why? Many thanks.

Reply to
Whatever I Fear
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For all intents and purposes, you can assume that water conducts electricity. How well it conducts depends on what is dissolved in the water and to what concentration. It is difficult to get water that is pure enough to be considered an insulator.

The water will act as a resistance connected in parallel with your device. At best, this will certainly affect your reading, making it unreliable, (especially as the resistance of the water may change). At worst it will act as a dead short - as if you soldered your two pads on the device together.

How this will affect the output signal will depend on what sort of device you are putting in the water. Some devices respond to their input by changing their own resistance - up or down, depending on the device (e.g. a thermistor, used to measure temperature electronically.) Simplified, their output is read by putting a voltage across them and measuring how much current flows. With your wet device, the electrical current can, at least in part, flow directly from the one soldered point to the other, bypassing the device itself. More current will flow than would normally occur, giving false readings. If enough current flows, and the circuit is not protected in some way from overcurrents, then the equipment reading the signal may be damaged (short-circuit).

Other devices generate a tiny voltage of their own, which can be measured. An example of this would be a moving coil microphone. In this case, the signal *should* be causing a tiny current to flow in the wires leading back up to your main equipment, but with the water providing an alternative path for the current, at least some of the current will short straight across the terminals of your device, bypassing your main equipment altogether. The signal will be reduced in intensity or lost entirely.

I would suggest using a waterproof device and making sure that your connections are insulated and waterproofed, too.

Disclaimer: you should make yourself aware of the dangers of mixing electricity and water. I don't know whether this is an academic exercise or an engineering project, so I've concentrated solely on your question.

Hope this helps.

Reply to
gentlish

piss on it !

Reply to
Nicky Payne

Water can present an impedance from the megohm range for pure water to hundreds of ohms or less for salt water. It is certainly going to tell you more about the ionization level of the water than what the strain gauge is reporting.

Reply to
gfretwell

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