TLDR:
I need advice on modeling water conductivity. Can it be modelled primarily as a simple resistance, or are capacitance and inductance high enough to be significant factors? Are there non-linear properties (will the apparent resistance or impedance be totally different depending on what voltage and/or current you use to test it?)
Full description/background:
I'd like to create a simple, crude, ballpark-approximation model of water conductivity in LTspice. This is tap water (ideally, filtered and de-chlorinated) and depending where in the world a machine is being installed, it might have TDS ranging anywhere from 50-75 ppm TDS (Seattle has great, fairly pure water) through 300-350 ppm TDS (Midwest, harder water, but not horrible) up to much higher levels where the water gets kind of gross and I'd rather not think about it!
I'm currently working on analyzing several different circuits that are all meant to detect water level in a tank. To be clear, the circuit only needs to determine whether water is touching a metal probe or not, not determine how full it is with any greater precision than that. Simple boolean state: water is high enough to touch probe or not.
In all of the circuits in question, the tank is metal, it is connected to the circuit common(ground,) and it is used as part of the detection circuit. The circuits send alternating positive and negative pulses to the probe and then they monitor the voltage at the probe. If there is water touching the probe, the current from the pulse will "ground out," or conduct through the water to the common/ground connection at the tank, resulting in lower voltage at the probe.
I've been toying with all of these circuits in LTspice, but so far I've been modelling the water as a simple resistance anywhere from 10k (maybe too low?) all the way up to 10M. I realized at one point that some of my circuit tweaks that look great in simulation would probably fail miserably if real world water has too much stray capacitance (or maybe inductance too?)
I'd like to improve my water model. Any advice on plausible ranges of resistance, capacitance, inductance, or any non-linearities would be greatly appreciated. Thanks!
I need advice on modeling water conductivity. Can it be modelled primarily as a simple resistance, or are capacitance and inductance high enough to be significant factors? Are there non-linear properties (will the apparent resistance or impedance be totally different depending on what voltage and/or current you use to test it?)
Full description/background:
I'd like to create a simple, crude, ballpark-approximation model of water conductivity in LTspice. This is tap water (ideally, filtered and de-chlorinated) and depending where in the world a machine is being installed, it might have TDS ranging anywhere from 50-75 ppm TDS (Seattle has great, fairly pure water) through 300-350 ppm TDS (Midwest, harder water, but not horrible) up to much higher levels where the water gets kind of gross and I'd rather not think about it!
I'm currently working on analyzing several different circuits that are all meant to detect water level in a tank. To be clear, the circuit only needs to determine whether water is touching a metal probe or not, not determine how full it is with any greater precision than that. Simple boolean state: water is high enough to touch probe or not.
In all of the circuits in question, the tank is metal, it is connected to the circuit common(ground,) and it is used as part of the detection circuit. The circuits send alternating positive and negative pulses to the probe and then they monitor the voltage at the probe. If there is water touching the probe, the current from the pulse will "ground out," or conduct through the water to the common/ground connection at the tank, resulting in lower voltage at the probe.
I've been toying with all of these circuits in LTspice, but so far I've been modelling the water as a simple resistance anywhere from 10k (maybe too low?) all the way up to 10M. I realized at one point that some of my circuit tweaks that look great in simulation would probably fail miserably if real world water has too much stray capacitance (or maybe inductance too?)
I'd like to improve my water model. Any advice on plausible ranges of resistance, capacitance, inductance, or any non-linearities would be greatly appreciated. Thanks!