TI started a design contest for that chip back in October. I think I heard about it via EDN magazine or maybe an email. At the last minute I did submit an entry, (which has been accepted for round 2) in order to get the design kit to play with. My entry would use it as a non-contact means to measure water conductivity. Water acts as a single turn secondary linking a toroid, and the dissipation in the water (conductance) reflects back to the primary. The principle of those things is well known, of course, but the deal with the TI chip is the level of integration.
What can be deduced about the water by knowing its level of conductivity? Guessing that pure water is a fair insulator, conductivity could/would/maybe indicate levels of contaminants?
I would be interested to see that circuit. What kind of resolution can you get pointing your inductive sensor at water?
I'm curious because years ago (1995) the company I worked for had a joint technology transfer exchange program with TAFB (Tinker Air Force Base).... Prior to a solution that I collaborated with, the method of paint removal on their airplanes involved a high power water jet and a capacitive sensor mounted on the water jet to determine distance of the sprayer from the aircraft. The water contributed to the capacitor dielectric of the sensor, causing erroneous distance readings. By modifying their existing sensor arrangement and using an inductive approach instead of capacitive approach, resulted in a much better solution for them that was impervious to water which could maintain accurate position sensing at a specific distance from the plane.
Beau, I'm appreciative of your input. I'm going to have to bone up on Maxwell's equations and the options for doing this project. The device I'm thinking about is immersed in a body of water, so your phrase "pointing your inductive sensor at water" does not apply. The water has to form a conductive path all the way around the toroid so that it can support an electrical current.
I take it your device was detecting the metal in the aircraft? I'm not picturing how it was set up.
Dave, These non-contact conductivity sensors are used in industrial process control, as an indicator and as feedback for correct "saltiness". It would test the hardness of your well water. They are great for environmental tracking, in estuaries in particular where there is mixing of salt and fresh water. In fresh water you might be looking for contamination by fertilizer. There are natural cycles, for example, surface runoff from a storm generally has low conductivity, but water that has run underground for a length of time in the water table is more conductive as it picks up minerals.
The non-contact type is set apart from the type of cell that makes direct contact with water, which can be very sensitive, but also very hard to maintain for long deployments.
"The water has to form a conductive path all the way around the toroid so that it can support an electrical current" - Interesting...don't think I have tried that arrangement. I've passed enough current through a coiled 1/4 inch PVC tubing filled with water to get a magnetic reading, so I don't doubt you, I'm just curious essentially going the other direction, what resolution you are able to obtain using the body of water as a secondary coil shunt.
"I take it your device was detecting the metal in the aircraft? I'm not picturing how it was set up." - Yes, these particular aircraft had an all metal exterior allowing this operation to work. Some areas were blocked and needed to be done manually such as near the windshield, etc. The sense 'coil' was about a 1 foot diameter pancake coil.
Beau, the way it is usually done is not with solenoid winding. It is a toroid wound on a ferrite core, so there is very little leakage flux. AC Current through the winding causes a time-varying magnetic flux, a loop of flux in the core. Then by Faraday's law, there is an electric field proportional to the rate of change of flux along a path that passes through the center of the toroid. If there is a wire or conductive medium along that path, it will carry a current due to the electric field. There is an easier alternative way to think of it: The extra loop is a single turn wrapped around the toroid, the secondary of a toriodal transformer. Commercial conductivity meters of this type usually use a pair of toroids, set side by side, so the current produced by one links the other as well, and the 2nd one acts as a pickup, stepup coil. So the whole thing is a 3-winding transformer with the intermediate link being the conductive fluid.
davejames
Posts: 4,047
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Mr. Allen,
What can be deduced about the water by knowing its level of conductivity? Guessing that pure water is a fair insulator, conductivity could/would/maybe indicate levels of contaminants?
I would be interested to see that circuit. What kind of resolution can you get pointing your inductive sensor at water?
I'm curious because years ago (1995) the company I worked for had a joint technology transfer exchange program with TAFB (Tinker Air Force Base).... Prior to a solution that I collaborated with, the method of paint removal on their airplanes involved a high power water jet and a capacitive sensor mounted on the water jet to determine distance of the sprayer from the aircraft. The water contributed to the capacitor dielectric of the sensor, causing erroneous distance readings. By modifying their existing sensor arrangement and using an inductive approach instead of capacitive approach, resulted in a much better solution for them that was impervious to water which could maintain accurate position sensing at a specific distance from the plane.
I take it your device was detecting the metal in the aircraft? I'm not picturing how it was set up.
Dave, These non-contact conductivity sensors are used in industrial process control, as an indicator and as feedback for correct "saltiness". It would test the hardness of your well water. They are great for environmental tracking, in estuaries in particular where there is mixing of salt and fresh water. In fresh water you might be looking for contamination by fertilizer. There are natural cycles, for example, surface runoff from a storm generally has low conductivity, but water that has run underground for a length of time in the water table is more conductive as it picks up minerals.
The non-contact type is set apart from the type of cell that makes direct contact with water, which can be very sensitive, but also very hard to maintain for long deployments.
"I take it your device was detecting the metal in the aircraft? I'm not picturing how it was set up." - Yes, these particular aircraft had an all metal exterior allowing this operation to work. Some areas were blocked and needed to be done manually such as near the windshield, etc. The sense 'coil' was about a 1 foot diameter pancake coil.