Electricity: measuring and testing – Magnetic – Calibration
Reexamination Certificate
1998-10-01
2001-03-27
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Calibration
C324S207130, C324S207240
Reexamination Certificate
active
06208133
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and apparatus for calibrating the output signal of linear position detectors, and, in one preferred embodiment, to a calibration system for defining reference points in a linear position detector in which energy, such as magnetic energy, is provided on the exterior of the detector housing and received by a sensor within the housing, so that the housing need not be opened during calibration, thereby preserving the moisture resistant housing seal.
BACKGROUND OF THE INVENTION
A magnetostrictive linear position detector typically includes a magnetostrictive waveguide wire which is housed in a protective waveguide housing about which a magnet is slidingly engaged. A current pulse is sent through a wire near the waveguide (or through the waveguide itself), and this pulse interacts with the magnetic energy of the magnet to induce a torsional strain wave in the magnetostrictive waveguide at the location of the magnet. The strain wave travels along the length of the waveguide and passes through a mode convertor, such as a pickup coil, which converts the mechanical wave into an electrical signal. To obtain the location of the magnet, the time between the transmission of the current pulse and the reception of the signal from the coil can be measured and converted to a distance, because the speed that the torsional wave will travel along the waveguide is known. Accordingly, when the magnet is connected to a movable mass, such as a liquid level quantity in a storage tank, or a movable element in a machine tool for example, the exact position of the mass can be measured and monitored.
In more advanced magnetostrictive linear position detectors, the ability to set reference points along the measurement stroke is provided. For example, in some such sensors, the magnet can be positioned at any location along the waveguide housing, and a button or buttons can be pressed to save the current position of the magnet in memory so that this position can be used as a reference point. In some systems, the output signal to be provided at this reference point car be assigned, such as by manipulating the programming buttons. Additional reference points can also be assigned and utilized in a similar manner.
Such calibration systems allow the output of the transducer to be changed from the original setup provided by the manufacturer. For example, while the manufacturer might configure the transducer to provide a 0 volt output when the magnet is at one end of the waveguide housing and a 10 volt output when at the opposite end, the ultimate user of the transducer may desire different settings. With such a calibration system, the user could assign any possible voltage output to any of the possible magnet positions. For example, the user may wish that a position 2 inches (50.8 mm) from the first end provides a 0 volt output, and that a position 3 inches (76.2 mm) from the opposite end provides a 10 volt output. By using such a calibration system, these reference points can be assigned the desired outputs. Once the reference points are assigned, the system can then be set up to scale all subsequent magnet positions based upon the reference points.
Accordingly, the programmability or adjustability of reference points allow the user to customize the sensor to provide the desired output range over the desired measurement stroke. Thus, a reference point can be, for example, an endpoint of the stroke.
However, such calibration systems are not without disadvantages. For example, such systems can expose the electronics to potential damage. More specifically, to access the programming buttons, screws or other covers on the electronics housing must be removed, and the buttons can then be depressed by extending a pin or screw driver through the resulting access openings. However, providing such access openings, even when sealed off by screws and the like, can compromise the ability of the housing to seal off moisture and other contaminates which can damage the delicate electronic components inside. In many applications, an excellent watertight seal is required, such an IP67 rated seal, and access openings generally diminish the ability of the housing to achieve and maintain such a seal.
Moreover, if the screw or cover is lost or is not properly replaced over the access opening after the desired programming has been conducted, the seal is again compromised or lost. In addition, the device used to depress the programming buttons, such as a screwdriver, pin, or finger, can carry electrostatic charge which can itself damage electronic components within the housing.
Accordingly, it is desirable to provide a system and method for calibrating a linear position detector which does not affect the ability of the transducer's electronics housing to protect against undesirable ambient and external moisture, contaminates, and electrostatic discharge, and which does not require opening and closing or other physical access through the housing for programming the detector.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to obviate the above-described problems.
It is another object of the present invention to provide a linear position detector having adjustable output capability while also providing good protection from moisture and contaminants.
Another object of the present invention is to provide a system and method for calibrating the output signal of a linear position detector which eliminates the need to provide access openings to the interior of the transducer housing.
Yet another object of the present invention is to provide a system and method for calibrating the output signal of a linear position detector which minimizes the risk of damaging electronic components.
It is another object of the invention to provide a linear position detector with adjustable output capability that includes a simpler electronics housing design.
Yet another object of the present invention is to provide a linear position detector which can be calibrated in a simpler and more efficient manner.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described above, a calibration system for a linear position detector having a movable marker is provided. According to the present invention, the system comprises a housing having a wall and an energy source located exterior to the housing. An energy sensor is located within the housing and arranged for selective communication with the energy source through the housing wall. A processor is also located within the housing and arranged in communication with the sensor. The processor is adapted to define a reference point based upon the current position of the marker when the energy sensor receives a predetermined energy signal from the energy source. Preferably, the energy source is a magnet and the energy sensor is a Hall effect sensor, although other sources of energy could be utilized, such as sources of electromagnetic or electrical energy.
The energy source could be coupled to a base having an attachment mechanism adapted to attach the base adjacent the exterior of a housing of a linear position detector. In addition, the energy source could be selectively movable from a home position to a selection position.
According to the present invention, a method for calibrating the output signal of a linear position detector having a housing and movable marker is provided. The method comprises selectively providing energy from a location exterior of the housing, sensing the presence of the energy, and, upon sensing the energy, defining a reference point based upon the current position of the movable marker.
A calibration system for a linear displacement detector having a movable marker is provided according to the principles of the present invention. The system comprises a housing, an activator located exterior to the housing, and a processor located within the housing. The activator is adapted to selectively apply an energy signal from an energy source through the housin
Ehling Ernst
Gass Ernst
Kurz Martin
Ullrich Andreas
Balluff, Inc.
Dinsmore & Shohl LLP
Patidar Jay
LandOfFree
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