Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With electromagnetic field
Reexamination Certificate
2000-09-15
2002-03-26
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With electromagnetic field
C324S119000, C324S132000
Reexamination Certificate
active
06362616
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to analog gauges and specifically to flat response temperature circuitry for analog gauges yielding a decreased parts count and increased control over a “flat zone” of the gauge.
2. Description of Related Art
Analog gauges are commonly used to display automobile data to a driver. In a typical analog gauge, electrical current flows through wire coils disposed about a permanent magnet. The amount of electrical current flowing through each coil varies according to the value of a measurand at a remote location.
As current flows through each coil, a magnetic field B is induced proximal to the coil. The direction of the magnetic field is determined by the direction of the winding of the coil as given by the right-hand-rule. In general, a stronger magnetic field can be created by allowing more current to pass through a given coil. The strength and direction of the magnetic field can be represented by a vector having a magnitude corresponding to the strength of the magnetic field and a direction corresponding to the direction of the induced magnetic field.
The magnetic fields induced about each coil combine to create a resultant magnetic force which is, in terms of direction, followed by the permanent magnet about which the coils are disposed. The permanent magnet is attached to a rotatable shaft that is attached to a pointer arm that moves over a dial face in response to changes in the direction of the resultant force. Circuitry, attached to the coils, varies the relative current flow in each coil to change the resultant magnetic vector corresponding to the value of the measurand at the remote location. If the measurand changes, the direction of the resultant force will change and the shaft and pointer will rotate accordingly.
In a linear gauge, the shaft responds in a linear relationship to changes in the measurand at the remote location. For example, in a linear temperature gauge, a 20% change in temperature causes a 20% rotation in the magnet, shaft, and pointer. Alternatively, the responsiveness of the gauge can be reduced for a predetermined range of temperatures. Such a gauge is commonly referred to as a “flat response” gauge because a “flat zone” is created in which the circuitry of the gauge has a reduced level of responsiveness to changes in the measurand.
The prior art circuit of
FIG. 1A
is exemplary and provides for a power source
10
such as a DC battery and a bridge resistor
12
having one terminal connected to the power source
10
and one terminal connected to a sender resistor
14
such as a thermistor. The sender resistor
14
has its remaining terminal connected to ground. This sender resistor
14
has an operating resistance of 275−18.3 &OHgr;.
Further connected to the power source
10
is a first coil L
1
having one terminal connected to the power source
10
and one terminal connected to a second coil L
2
. L
2
is in series with L
1
and has its remaining terminal connected to a third coil L
3
. L
3
has one terminal connected to L
2
and one terminal connected to a fourth coil L
4
. L
4
has its remaining terminal connected to an anode of first diode
16
whose cathode
16
C is connected to ground.
L
3
, L
4
, and the first diode
16
are connected in series, and L
1
is wound about a first axis, L
2
and L
3
are counterwound about the same first axis, and L
4
is counterwound about a second axis which is magnetically orthogonal to the first axis. L
1
and L
2
are formed from a single piece of uninterrupted wire having a resistance of 235.2 &OHgr;, and L
3
and L
4
are formed from a single piece of uninterrupted wire having a resistance of 100.6 &OHgr;. L
1
comprises 1290 turns of wire; L
2
, 490 turns; L
3
, 630 turns; and L
4
, 310 turns.
The prior art circuit further includes a zener diode
18
connected at its anode
18
A to the common terminal between L
2
and L
3
and at its cathode
18
C to the common terminal between the bridge resistor
12
and the sender resistor
14
. The zener diode
18
is a 3.6 V, 1 W zener diode, and, dependent on the resistance of the sender resistor
14
, it provides a current path when reverse biased or forward biased, as will be elaborated upon below. The zener diode
18
, in conjunction with the resistance of the sender resistor
14
, establishes the flat zone responsiveness of the circuit.
Referring now to
FIG. 1B
, the magnetic fields induced by the electrical currents flowing through each coil L
1
-L
4
are depicted by individual vectors B
1
-B
4
, respectively, each vector having a magnitude corresponding to the strength of the related magnetic field and a direction corresponding to the direction of the related magnetic field according to the right hand rule oriented along the appropriate winding axis. Because coils L
1
, L
2
, and L
3
are wound about the same magnetic axis, their respective magnetic fields, B
1
, B
2
, and B
3
, lie along a common axis. Stronger magnetic fields are represented by vectors having greater magnitudes along the appropriate axes, and the direction of the magnetic fields induced by coils L
2
and L
3
(i.e., B
2
and B
3
, respectively) are aligned with one another because both are wound about the same axis in the same direction, as opposed to the magnetic field induced by coil L
1
(i.e., B
1
), which is counterwound about the same magnetic axis in the opposite direction. The magnetic field induced by coil L
1
therefore magnetically opposes the fields induced by coils L
2
and L
3
. The magnetic field induced by coil L
4
(i.e., B
4
) is magnetically orthogonal to the magnetic field induced by coils L
1
-L
3
because L
4
is wound about a second axis which is magnetically orthogonal to the first. What is needed, however, is circuitry having magnetic fields induced in all four directions from the common origin located at the intersection of the winding axes of the coils L
1
-L
4
.
Finally, a resultant magnetic force acting on the permanent magnet can be represented by a resultant vector B having a magnitude and direction which is equal to the sum of the individual magnitudes and directions of the magnetic fields B
1
-B
4
induced by the coils L
1
-L
4
, respectively. The direction of the resultant vector corresponds to the direction of the resultant force and determines the amount of rotation of the permanent magnet, shaft, and pointer, which are fixedly attached to one another.
Unfortunately, however, traditional flat response circuitry has significant drawbacks. For example, a diode must be connected in series between ground and L
4
. That is, the coil that is furthest from the power source, in order to provide a voltage drop to allow adjusting the flat zone responsiveness of the circuit. Moreover, different manufacturers require different flat response curves for arbitrary sender resistances, and the circuitry of the prior art does not allow the flexibility required to implement different flat response curves.
What is needed, therefore, is circuitry allowing increased control over the flat zone responsiveness of a non-linear gauge. Such circuitry must be flexible enough to meet the demands of numerous manufacturers utilizing different sender resistors and demanding differing levels of angular displacements of the pointer arm over the dial face.
BRIEF SUMMARY OF THE INVENTION
Briefly, the circuitry of the present invention comprises a plurality of coils wound about a first axis and a plurality of coils wound about a second axis, the second axis being magnetically orthogonal to the first axis. A single zener diode is provided having its cathode connected to a common terminal between a bridge resistor and a sender resistor and its anode connected to a common terminal between the coils wound about the second axis. In an embodiment described below, the sender resistor is a thermistor and the zener diode conducts in a forward or reverse direction dependent upon the resistance of the sender resistor
Quarles & Brady LLP
Strecker Gerard R.
Visteon Global Technologies Inc.
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