Measuring and testing – Liquid level or depth gauge – Immersible electrode type
Reexamination Certificate
2003-09-15
2004-11-23
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Immersible electrode type
C073S30400R, C073S29000R
Reexamination Certificate
active
06820483
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a simple non-moving passive electric probe along with circuitry to detect the height of water-based solutions on its surface. The probe operates in areas where other level sensors such as floats, optical or ultrasonic types cannot operate reliably. These would include areas where high flow rates, significant liquid agitation, or air and liquid foaming make other sensors ineffective. Such areas would include inside pipes, and pumped wastewater or sewage tanks.
Sewage or sump applications can be troublesome due to the presence of oils, fats or other non-conductive hydrocarbons. Oils will usually float on the surface of the water and have high surface tension. They can coat the surface of the sensing probe such that it will no longer make connection with the water underneath. This invention includes a means to break this film allowing the probe to continue working.
The most popular, and not coincidentally, the least expensive form of liquid level sensing is the float control. It consists of a body that will float on water with either an enclosed tilt switch or an embedded magnet that moves with the float to make or break a switch contact. Its disadvantage is it must move to work. If the float is subjected to the force of the water or is thrown around like a boat on a rough sea, false activations are common. If it pounds against the sides of its container or the pump's steel case it will eventually break apart, leak, and sink. In sewage applications sticky, slimy, disgusting items will become entangled in its cord or wrap around its bearing surfaces, drying and hardening like a rock, preventing long term reliability without periodic cleaning.
Water resistance sensing is a well-known means of detecting a water level. Its disadvantage is that it only detects the presence or absence of water and does not produce a true level signal output. It must be set to sense the highest resistance water it is likely to encounter (5-megohms) and this leads to another problem. Once water wets its sensing areas, a thin water film remains behind and continues to conduct. Even if the water film completely evaporates conductive salts or oxides will remain behind continuing to supply resistance. As such, these problems limit this technology to non-critical applications.
Other than floating or resistance sensing mentioned above there is a whole range of liquid level detectors that include capacitive, ultrasonic, magnetic, crystal, optical, resonant, and oscillating types. These means generally depend on a relatively quiet, flat, non-agitated water surface for their reliable operation.
The technical field of this invention relates to the science of electrical charges in water-based solutions including redox reactions, galvanic cells, and electrolytic cells. Some limited explanation here will clarify this inventors understanding of the relationship between the area wet on a conductive probe, voltage and current in water reactions. This is explained in terms of electricity not chemistry due to the author's primary area of expertise.
In
FIG. 1
, place a cast iron pump (
1
) and a copper probe (
14
) in pure, distilled non-conductive water (
15
), and a spontaneous negative voltage will be present on the Iron (
1
) and a positive voltage will appear on the copper probe (
14
). Since the water is not conductive, electrons themselves cannot make the trip from copper to iron. Remove the copper probe, insert an aluminum probe and the voltage reverses, a spontaneous positive voltage will be present on the iron and a negative voltage will appear on the aluminum. This reaction between dissimilar periodic conductive elements is well known and referred to as a dielectric effect.
Powering this whole process is the oxidation of the negatively charged electrode, in the Iron-Copper example; the iron visibly rusts, combines with oxygen and generates the electrical energy. Remove the copper probe and insert a magnesium probe and the polarity, chemistry reverses, the magnesium visibly rusts, and the iron stops rusting. Remove the waters access to air and the process stops, the voltage falls to zero, no current generates and rusting stops. Oxidation occurs at the iron-water interface and reduction occurs at the water-copper interface; this is termed a redox reaction.
Connect the iron pump to the magnesium probe with an external wire and an electrical current will flow. Allow this current to flow for some time and magnesium will be plated onto the surface of the iron. This inventor hypothesizes that a particle with a positive charge left the magnesium leaving electrons behind and traveled through the water to the iron. In addition, because electrons are not carrying the charge through a conductor the process is much slower than the speed of light. This is evidenced by the speed of the build up of voltage and current on the probe.
A chemically generated, electrically motivated, particle is mechanically traveling, moving charges through non-conductive water. Likened to a Van De Graph Generator where a non-conductive moving rubber belt carries electrical charges from a conductive ground to a conductive sphere. Similarly, electrical charges taken from the surface of a grounded iron pump travel through a non-conductive solution and change the charge on a copper probe. Like the Van De Graph generator, the voltage produced rises as time elapses gathering more and more electrical charges on the opposite electrode.
Surprisingly, and unlike the Van De Graph generator, this reaction's voltage self limits at very low and very specific voltages, usually less than 2-volts. The limiting voltage is independent of solution conductivity, the distance between the electrodes and the level of the water and totally dependent on the electrode materials themselves. This effect is well known and even categorized in tables of electro negativity. The voltage should have continued to increase towards infinity as more and more charged particles moved through the solution but something stops it. The example, iron-water-copper reaction quickly builds to 0.62-volts and then stops.
It is reasonable to assume the process limited itself when the aforementioned charged particles in the water stopped moving. Stacking up, waiting to get at a limited surface area they back up all the way to the source electrode and stop particles from leaving. Charged particles will not leave the source electrode if the solution is already full of particles at the same potential, since like charges repel. The critical voltage noted must be equal to the electrical force required to stop these particles from moving or leaving their source. Once this electromotive force has been achieved the reaction is at equilibrium where no new particles are created, no particles move through the solution, and none are collected. The electromotive force required to stop the reaction is different for each differing set of electrode elements. This inventor concludes that the voltage is not indicative of how fast the reaction proceeds, just how much force is required to stop it.
I supposed that electrodes that produced higher voltages would also produce higher currents; this was not necessarily the case. Some conductive electrodes produced high voltages but once shorted through a current sensor developed very little current flow. This inventor hypothesizes that while the voltage indicates the force stopping the reaction the current signifies how fast the reaction is proceeding; or how many charged particles per second make the trip through the solution. Current flow increases by shortening the distance between the dielectrics, or by increasing their surface area. This seems to support the hypothesis.
This inventor concludes that more surface area allows more particles per second access to the solution at the source electrode and allows more particles per second access to the receiving electrode. With the dielectrics open circuited more surface area shortens the time interval to reach the critical voltage where the reaction stops.
Frank Rodney T.
Mechanical Ingenuity Corp.
Williams Hezron
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