To detect the volume or level of fluid in your tanks, ESI offers a wide range of traditional and advanced sensing technologies for your tank sensor, including:
Mechanical tank sensors are the original and traditional sensing devices. Most commonly, they sense the position of a float, floating on the fluid, by a mechanical linkage inside or outside the tank. Mechanical tank sensors have generally been replaced in our systems by more modern sensors (see below).
Magnetic tank sensors commonly sense the position of a float by a mechanical linkage attached from a float to a magnet. More modern magnetic sensing uses “Hall effect” sensors attached to the gauge of mechanical sensor. (This is a common way of sensing propane tanks, for instance). The “Hall effect” sensor is normally mounted on the mechanical sensor’s gauge, and senses the position of a magnetized indicator needle on the mechanical sensor’s gauge. This requires the gauge to be “Hall effect ready” or “magnetic ready” (equipped with a magnetized indicator needle), as many now are.
- PRESSURE (Hydrostatic, Bubbler & Differential)
Pressure sensors come in multiple types, particularly:
A hydrostatic tank sensor typically senses the pressure of the fluid at the bottom of the tank. The amount of pressure depends upon the weight of the fluid above the sensor, which, of course, depends upon the amount of fluid in the tank. These are, by far, the most popular modern tank sensor type, and are widely used in almost every type of fluid, worldwide. Hydrostatic sensors are available for most fluids, including corrosive, volatile and flammable fluids. Intrinsically safe sensor types, which limit electrical energy in the tank, are available.
A “bubbler” tank monitor uses a pneumatic sensor above the fluid, attached to a tube that reaches the bottom of the tank, and a very small air pump to pressurize the tube. When the pump activates, it pressurizes the tube until the pressure is high enough to force air out the bottom of the tube, at the bottom of the tank. The amount of pressure required to force the air out the bottom of the tube depends upon the pressure at the bottom of the tank — a pressure that results from the amount of fluid in the tank. As the pump pressurizes the tube, the pneumatic sensor detects the rise in air pressure in the tube, and reports it to the tank monitor system. When the pressure is finally enough to force the air out the bottom, the pressure stops rising and becomes constant — and the tank monitor system notes that pressure as the pressure at the bottom of the tank. That pressure indicates the amount of total fluid in the tank, pressing down on the bottom.
Bubblers are particularly low-cost, high-reliability systems that are best suited to vented, non-pressurized tanks, containing non-volatile, non-hazardous fluids. A unique advantage of bubbler units is that their system of operation tends to make them “self-cleaning.” They are especially popular for monitoring water, oil, waste oil, coatings, concrete additives, slurry and paper pulp mix.
A differential pressure sensor detects the difference in pressure between the top and bottom of a tank; and translates that into a quantity of fluid. This is particularly useful for sensing fluids in a non-vented tank, such as cryogenic fluids, or tanks where vapor is generally confined to the tank, as with gasoline. Differential pressure sensors are more expensive than ordinary pressure sensors, so are generally used only where necessary.
- ELECTROSTATIC (Capacitive / Inductive):
Electrostatic tank monitoring is thorough an electrostatic sensor that detects the tendency of a fluid, or a measuring device in the fluid, to store, convert or pass electrical energy. These are either capacitive or inductive sensors. Typically, electrostatic tank sensors detect the amount of fluid in the tank by sensing the electrical capacitance of the fluid (its ability to hold a very faint, tiny electrical charge). The measured capacitance depends upon the type of fluid, and the percentage of the sensor probe that is immersed in it (determined by the height of the fluid in the tank). The effectiveness of this type of sensor largely depends upon the “dielectric” (electrical capacity) of the particular fluid (oil and water have different “dielectric” values, for instance), and the type and size of tank.
Electrostatic sensors are commonly used for measuring fluids such as water, oil, fuel, other petrochemicals and solvents, and certain chemcials — especially in metal tanks, totes or drums, and in other specialized applications.
Ultrasonic tank sensors (normally mounted in the top of a tank) use a very high frequency sound (“ultrasound”), at a pitch higher than humans can hear, to blast a momentary “ping” noise, which bounces (“echoes”) off of the surface of the fluid. The tank monitor detects the microscopic time delay between when it sends the “ping” and when it “hears” the ping’s “echo”. The longer the time, the farther away the surface of the fluid, and the lower the level of the fluid in the tank. The monitor calculates the level of the fluid in the tank from this “echo delay”.
Ultrasonic sensors are popular for a very wide range of fluids, and can be especially popular for tanks where non-contact with the fluid is desired.
A radar tank sensor operates on much the same principle as the ultrasonic tank sensor (above), except tha the “ping” is sent by a much-higher-frequency radio wave. An advantage of radar is its greater ability to penetrate through vapor, mist and dust, to more clearly “see” the surface level of the fluid (or granular solid) in the tank, and its capacity for extremely high precision.
ESI sensors come in either 4-20 mA or 0-5 volt indications, matched to the monitor of your choice.
With the wide range of sensor options to probe your tanks (of any size or shape),
we can probably measure any kind of fluid you have, including:
- Industrial Chemicals (solvents, alkaloids, acids, resins, coatings, additives, suspensions, slurry, paper pulp mix, etc.)
- Cryogenics (liquified/compressed gasses, propane, etc.)
- Agricultural (pesticides, herbicides, fertilizers & feeds)
- Foods & Beverages
- Water & Wastewater
- …and virtually any other fluid.
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