Abstract:
An adapter for a mechanical type levelmeter, which has a magnet that moves in response to a changing level of liquid in a container. The adapter is fitted onto the levelmeter in a manner that is transparent to any existing reading dials, but that permits hall sensors on the adapter to respond to the motion of the magnet. The adapter also has a processing unit and a transmitter, which process the output of hall sensors and generate a transmittable signal representing level data.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to measurement devices, and more particularly to an adapter for a levelmeter, which enables the levelmeter to be remotely monitored. 
     BACKGROUND OF THE INVENTION 
     Level sensing is used for a vast number of applications, perhaps the most familiar being for tanks containing liquids, such as fuel tanks. A limit levelmeter (also known as a switch levelmeter) provides readings at one or more predetermined levels. For example, a limit levelmeter may provide a reading only at a predetermined low level. A continuous levelmeter provides a continuous range of measurements from empty to full. 
     There are many different types of level meters, each type having a different principle of operation. Some of the more common types are float levelmeters, capacitive levelmeters, photoelectric levelmeters, and ultrasonic levelmeters. 
     Most levelmeters are designed to provide a readout at the meter. However, in light of today&#39;s ever increasing data networking capabilities, there is a demand for remote monitoring. Today, this is typically accomplished by removing a mechanical reading dial and replacing it with an electronic data device. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is a remote monitoring adapter for use with a levelmeter. It is assumed that the levelmeter is a mechanical device having a rotating magnet that operates a read out mechanism, such as a needle dial. The adapter comprises a probe having thin flat plate upon which is mounted at least one hall sensor operable to respond to motion of the magnet. The probe is of a size and shape suitable for insertion between the magnet and the read out mechanism. The adapter also has a processing unit that receives an output signal from each hall sensor and converts the sensor output to digital data representing a level of liquid. A transmitter is operable to provide a signal that represents the digital data and that may be transmitted to a remote monitoring unit. 
     One advantage of the invention is that the adapter does not modify the performance of the original levelmeter. In other words, the levelmeter&#39;s reading dial may still be read in the same manner as before installation of the adapter. Installation of the adapter is simple and quick. It can be installed in a tank already containing liquid; it is not necessary to empty the tank before installation. 
     The adapter is a low cost device. It can make either digital or analog readings, and can measure both liquid level and rate of consumption. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a levelmeter having a remote monitoring adapter in accordance with the invention. 
     FIG. 2A illustrates a digital version of the probe of the adapter of FIG.  1 . 
     FIG. 2B illustrates an analog version of the probe of the adapter of FIG.  1 . 
     FIG. 3A illustrates the adapter of FIG. 1 in further detail. 
     FIG. 3B illustrates a digital version of the processing unit of the adapter of FIGS. 1 and 3. 
     FIG. 3C illustrates an analog version of the processing unit of the adapter of FIGS. 1 and 3. 
     FIG. 4 illustrates a method of transmitting the monitoring signal over a pipeline. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a levelmeter  10  having a remote monitoring adapter  11 , in accordance with the invention. Although, not explicitly illustrated, it is assumed that levelmeter is installed in a container of some sort, which contains liquid. For purposes of this description, it is assumed that the container is a tank. FIG. 1 indicates the surface level of the liquid within the tank under the levelmeter  10  at float  13   b.    
     As explained below, the basic principle of operation of adapter  11  is the use of an adapter having a sensor probe that is inserted under the readout dial of a conventional levelmeter. The probe reads the magnetic field fluctuations generated by a rotating magnet associated with the levelmeter&#39;s float. Although levelmeter  10  is a float type meter in the example of this description, any levelmeter having a mechanism that activates a magnet in the same manner as magnet  13   b  could be used with adapter  11 . 
     Levelmeter  10  has two main components: a reading dial  12  and a main body  13 . It is assumed that reading dial  12  can be removed and replaced on the main body  13 . This may be accomplished with screws  14  or various other attachment means. 
     The main body&#39;s float  13   a  float on the surface of the liquid and moves up or down according to the liquid level in the container. A rotating magnet  13   b  has a mechanical connection to the float  13   a  that causes magnet  13   b  to rotate in response to movement of float  13   a . A needle  12   a  within reading dial  12  moves in response to the motion of magnet  13   b . In the example of this description, the rotation of magnet  13   b  and of needle  12   a  are in a plane parallel to the liquid surface, but other configurations are possible. For example, the reading dial  12  could be oriented at right angles to the surface, with magnet  13   b  and probe  11   a  repositioned accordingly. 
     Adapter  11  has three main components: a probe  11   a , processing unit  11   b , and transmitter  11   c . As explained below, the internal configuration of these components vary depending on whether adapter  11  provides a digital or analog output. A digital output is the type of output associated with limit or switch type levelmeters. An analog output permits continuous level information. 
     Probe  11   a  is essentially a thin flat plate, upon which is mounted one or more hall sensors, as described below in connection with FIGS. 2A and 2B. Probe  11   a  has a size and shape suitable to permit it to be placed between reading dial  12  and the main body  13 . Probe  11   a  may be easily implemented as a printed circuit board. 
     Probe  11   a  is transparent to the magnetic field generated by magnet  13   b . This transparency avoids interference with reading dial  12 . Accordingly, probe  11   a  is made from a non-ferromagnetic material such as a plastic, aluminum, or ceramic material. 
     However, probe  11   a  reads the magnetic field generated by magnet  13   b , producing current and voltage signals proportional to that field. A cable  15  connects probe  11   a  to processing unit  11   b.    
     Processing unit  11   b  performs signal amplification, conditioning, timing. It generates digital level data, which may represent either a discrete level or a rate of consumption. It also provides the power supply for adapter  11 . Processing unit  11   b  is further described below in connection with FIGS. 3A-3C. 
     Transmitter  11   c  receives the digital data from processing unit  11   b  and generates a signal suitable for transmission to a remote receiver. The transmission may be wireless or by means of cables or some other data network medium. 
     FIG. 2A illustrates a digital version of probe  11   a . The location of magnet  13   b  under probe  11   a  is indicated with dotted lines. As explained below, this version of probe  11   a  provides both a single level reading, as well as a rate of consumption. However, probe  11   a  could be configured with an appropriate sensor (or sensors) for only one of these types of readings. Also, additional sensors could be used to obtain additional readings for different levels of fullness. 
     In the digital version of FIG. 2A, three hall sensors  22 - 24  are placed on plate  21 , together with a magnetic field stretcher  25 . For the digital version of probe  11   a , sensors  22 - 24  are switch type sensors. Hall sensor  22  switches on when the north pole of magnet  13   b  approaches it. Typically, sensor  22  is positioned relative to magnet  13   b  so that it switches on when the tank has a predetermined “low” level of fullness. As indicated below, this low level may be the level allowable before an alarm indicates need for a refilling the tank. For example, the low level may be the level at which the tank is only 20% full. 
     Hall sensors  23  and  24  are used to determine the rate of consumption of the liquid within the tank. To do this, processing unit  11   a  makes one reading of the level at exact time periods. When sensor  24  switches on, processing unit  11   b  counts how many time periods elapse before sensor  23  switches on. The number of time periods is proportional to the inverse of the consumption rate. The distance between sensor  24  and sensor  23  on plate  21  may be small to reduce the counting time. 
     The counterclockwise movement of magnet  13   b  represents the tank being emptied. Ferromagnetic insert stretches the magnetic field to avoid a dead zone between sensors  24  and  23 . Insert  25  is an alternative to hysteresis of the switches because readings are made only when processing unit  11   b  gives a read command, the reading takes only a few seconds, and processing unit  11   b  puts adapter  11  in a “sleep” mode interrupting the power supply to probe  11   a . Insert  25  may be implemented with very small pieces of ferromagnetic material placed on or within plate  21 , thereby stretching the magnetic field and providing hysteresis and linearization. 
     FIG. 2B illustrates an analog version of probe  11   a . Two linear hall sensors  27  and  28  are placed on opposite sides of a ferro-magnetic strip, allowing differential readings of the magnetic field generated by magnet  13   b . Differential readings are advantageous due to the variation of magnet strength from one magnet to another and their aging process. The magnet placement calculates the position of magnet  13   b  independent of the strength of that magnet because the measurement is radiometric. Processing unit  13   b  then calculates the readings of sensor  27  and compares it with the sum of both sensors  27  and  28 . Those values are proportional to the position of magnet  13   b  relative to sensor  27 . 
     In the analog version of FIG. 2B, if the reading of sensor  27  is one-half the sum, magnet  13   b  is halfway between sensors  27  and  28 . Field stretcher  29  makes more linear the relationship between the angular movement of the magnet  13   b  and the output of processing unit  11   b . Field stretcher  29  may be fabricated from a thin layer of ferro-magnetic material. 
     Hall type sensors are characterized by their sensitivity to both static and dynamic magnetic fields. Any type of sensor falling within this category may be used. 
     FIG. 3A illustrates adapter  11  in further detail. The hall sensors in probe  11   a  (described above in connection with FIGS. 2A and 2B) are energized for only a few seconds. Power from processing unit  11   b  may be provided according to the number of readings in a set time period, such as one day. A timing and power control unit  31  sends energy from a battery to processing unit  11   b  and to transmitter  11   c.    
     As stated above, probe  11   a  is connected to processing unit  11   b  by means of a cable  15 , such as a multi-wire cable. Ground and positive voltage are provided by processing unit  11   b . Each hall sensor of probe  11   a  provides an associated output signal, which is carried to processing unit  11   b  by cable  15 . The outputs of the hall sensors  11   a  are processed by signal processor  32 . The type of processing depends on whether probe  11   a  is configured for digital or analog operation. 
     FIG. 3B illustrates signal processor  32  when probe  11   a  provides digital signals. A simple combinatorial logic unit  37  provides decisions according to the technique described above in connection with FIG. 2A. A protocol unit  38  performs tasks associated with rate evaluation, such as providing transmission of the information when necessary to get a level-time relationship preset according to the requirements of the system. It may also be used to prevent false evaluations of the consumption rate if the container is partially refilled. Output conditioner  39  adjusts the logic levels to those required by transmitter  11   c.    
     FIG. 3C illustrates signal processor  32  when probe  11   a  provides analog signals. The two hall sensors in probe  11   a  have two output signals (a and b). Appropriate logic elements  34  and  35  calculate the sum of both signals and the ratio of signal b to the sum. The output is then converted to a digital word by analog to digital converter  36 . 
     Regardless of whether probe  11   a  is digital or analog, the output of processing unit  11   b  is digital data that represents the level of the liquid contained in the tank. Transmitter  11   c  provides an appropriate interface to whatever transmission means is desired. 
     The liquid level data can be transmitted to a remote monitor to request refilling of the tank from a service provider or to otherwise inform a remote site of the level of the liquid within the tank. The transmission may use various intermediate devices; for example, the output signal from transmitter  11   c  may be used to operate an automatic telephone dialers. Various data communications systems may be used, such as by wire or radio frequency link. 
     FIG. 4 illustrates one embodiment of a transmission system, which uses a pipeline as a sound wave propagation medium. The remote monitoring signal is delivered as a complex digital signal in the form of sonic waves. Sound waves are desirable because sound travels more efficiently in solids, especially metals, than in air or liquids. The molecules in a solid are more tightly packed and sound waves are mechanical waves. 
     For example, the container with which levelmeter  10  is used might be a liquid propane tank. Such tanks have associated gas pipes, which deliver gas from the tank to appliances inside the building being served by the tank. It is also possible that the gas pipes might be linked to remote sites. 
     At adapter end of the pipeline communication system, transmitter  11   c  has a level adjuster  42 , which conditions the digital word from processing unit  11   b . For example, 0=x volts and 1=y volts. Encoder  43  forms a new digital word with the original level data and an identification code. Modulator  43  modulates the frequency of the output of oscillator  44 , a frequency corresponding to the resonant frequency of the transducer-pipe-transducer system. The output of modulator  43  is amplified by amplifier  45 , which drives the sound transducer  46 . 
     From transmitter  11   c , the sonic signal travels along pipe  47  to the sound transducer  51  in the receiver  40 . An amplifier  51  amplifies the signal to an automatic gain control unit  52 , which provides selective extra gain. Band pass filter  53 , which is tuned to the frequency of the oscillator  44  in transmitter  11   c . Filtering by a period discriminator  54  provides additional noise immunity. Comparator  55  reshapes the square waveforms, which are analyzed by decoder  56 . An output conditioner  57  has a digital latch to sustain the decoded information. 
     OTHER EMBODIMENTS 
     Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.