GB2058420A - Circuit for Use in the Detection of the Condition of an Isolated Switch Contact - Google Patents
Circuit for Use in the Detection of the Condition of an Isolated Switch Contact Download PDFInfo
- Publication number
- GB2058420A GB2058420A GB8027534A GB8027534A GB2058420A GB 2058420 A GB2058420 A GB 2058420A GB 8027534 A GB8027534 A GB 8027534A GB 8027534 A GB8027534 A GB 8027534A GB 2058420 A GB2058420 A GB 2058420A
- Authority
- GB
- United Kingdom
- Prior art keywords
- circuit
- output
- oscillator
- operational amplifier
- resistor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C23/00—Devices for measuring, signalling, controlling, or distributing tyre pressure or temperature, specially adapted for mounting on vehicles; Arrangement of tyre inflating devices on vehicles, e.g. of pumps or of tanks; Tyre cooling arrangements
- B60C23/02—Signalling devices actuated by tyre pressure
- B60C23/04—Signalling devices actuated by tyre pressure mounted on the wheel or tyre
- B60C23/0408—Signalling devices actuated by tyre pressure mounted on the wheel or tyre transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
- B60C23/0422—Signalling devices actuated by tyre pressure mounted on the wheel or tyre transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver characterised by the type of signal transmission means
- B60C23/0427—Near field transmission with inductive or capacitive coupling means
- B60C23/0428—Near field transmission with inductive or capacitive coupling means using passive wheel mounted resonance circuits
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B23/00—Alarms responsive to unspecified undesired or abnormal conditions
Abstract
A tyre pressure monitoring system includes a tuned circuit (10) comprising an inductor (11), with a pressure sensitive switch (13) which is closed when the tyre pressure is normal, connected across it, the tuned circuit and switch being mounted on a vehicle wheel. Mounted on a part of the vehicle is a detector circuit including an oscillator (14) which includes an inductor (15) which is at least intermittently magnetically coupled to the inductor (11) of the tuned circuit (10). When the switch (13) is closed the oscillator runs normally and its output is detected to indicate that all is well. When switch (13) is open, however, the oscillator output is suppressed whenever the inductors (11, 15) are coupled together. The circuit can also be used in other applications where it is required to detect the condition of an isolated switch contact. <IMAGE>
Description
SPECIFICATION
Circuit for Use in the Detection of the
Condition of an Isolated Switch Contact
This invention relates to a circuit for use in the detection of the condition of an isolated switch contact and has particular, but not exclusive, application to the monitoring of vehicle pneumatic tyre pressures wherein the switch contact is a tyre pressure sensitive device and is mounted on a vehicle wheel.
In vehicle tyre pressure monitoring applications many suggestions have been made for detecting the switch contact condition including arrangements in which there are magnetically operable switches and inductors connected in circuit with the contacts and these co-operate with permanent magnetics and pick-up windings on the vehicle. Other arrangements have been suggested in which a transmitter is provided on the vehicle which coacts with a pick-up circuit in series with the switch contact, which responds to the transmitter output dependent on whether the switch contact is open or closed.
None of the previously proposed circuits has been totally satisfactory in the sense that various malfunctions can occur which prevent the detector being able to distinguish between the contact open and contact closed conditions.
According to one aspect of the present invention there is provided a circuit for detecting the condition of an isolated switch contact comprising the combination of a tuned circuit including an inductor, said switch contact being connected in parallel with said tuned circuit, an oscillator circuit including a further inductor arranged to be at least intermittently magnetically coupled to the inductor of the tuned circuit, such that when the switch contact is closed the oscillator circuit continuously produces an oscillatory output, whereas when said switch is open and the inductors are magnetically coupled, the tuned circuit absorbs oscillations of the oscillator circuit and prevents the oscillator circuit from producing said oscillator output.
Preferably, the oscillator includes an amplifier having a resistive negative feedback path, and a positive feedback path shunted to "earth" by a further tuned circuit including said further inductor and a capacitor in parallel and tuned to the same resonant frequency as said first mentioned tuned circuit.
The amplifier is preferably an operational amplifier having a resistor connected between its output terminal and its inverting input terminal to define said negative feedback path, and also having a resistor connecting the output terminal to its non-inverting input terminal and said further tuned circuit connected between the noninverting input terminal and "earth".
The invention also resides in a vehicle tyre pressure monitoring system comprising a tuned circuit including an inductor, tyre pressure sensitive switch means connected in parallel with said tuned circuit and arranged to be closed when the associated tyre pressure is in excess of a predetermined level, said tuned circuit and said switch being mounted on a vehicle wheel assembly, an oscillator circuit also including an inductor mounted on a part of the vehicle such that the inductor of the oscillator circuit is magnetically coupled to the inductor of the tuned circuit at least periodically when the wheel is rotating, the arrangement being such that when the switch means is closed the oscillator circuit continuously produces an oscillatory output, whereas when said switch is open and the inductors are magnetically coupled, the tuned circuit absorbs oscillations of the oscillator circuit and prevents the oscillator circuit from producing said oscillatory signal.
In the accompanying drawings,
Figure 1 is a circuit diagram of one example of the invention, and
Figures 2 and 3 are circuit diagrams of two alternative forms of oscillator which can be used in the circuit of Figure 1.
Referring firstly to Figure 1, the system shown includes a passive tuned circuit 10 consisting of an inductor 11 and a capacitor 12, with a tyre pressure sensitive switch 13 connected in parallel with the inductor 11 and the capacitor 12. The tuned circuit 10 and the switch 1 3 are mounted on a rotating part of the wheel assembly of a vehicle with the pressure switch 1 3 sensing the pressure in the tyre on that wheel.
The system also includes an oscillator circuit 14 which is mounted on a fixed part of the vehicle so that it can be connected by wires to the vehicle battery and to a display on the vehicle dashboard (or elsewhere). The oscillator circuit is an LC sinewave oscillator and includes an inductor 1 5 and capacitor 1 7 of the same values as those used in the passive tuned circuit 10. The inductor 1 6 is situated so that as the wheel rotates the inductor 11 passes close to it and the two inductors are thus magnetically coupled periodically.The inductor 1 5 and the capacitor 1 7 are connected in parallel with one another between the noninverting input of an operational amplifier 1 8 and a reference voltage rail 1 9. The inverting input of amplifier 18 is connected by a resistor 20 to the rail 19 and by a resistor 21 to the output terminal of amplifier 18. The non-inverting input of the amplifier 1 8 is connected to its output terminal by a resistor 22 and a variable resistor 23 in series.
In the absence of the tuned circuit 10 the circuit surrounding amplifier 1 8 acts as an oscillator, the variable resistor 23 being adjusted so that the a.c. positive feedback at the resonant frequency of the tuned circuit 15, 1 7 exceeds the negative feedback via the resistor 21. When the tuned circuit 10 is brought into proximity to the inductor 15, however, and the switch 13 is open, the coupling between the inductors 11, 1 5 effectively decreases the impedance of the tuned circuit 15, 1 7 so that the a.c. positive feedback is reduced and oscillation ceases. When switch 13 is closed the oscillator is not affected by proximity of the tuned circuit 10, but oscillations continue.
A detector circuit 24 is connected to the output of the oscillator 14 and includes a capacitor 25 connecting the output of amplifier 18 to the cathode of a diode 26, the anode of which is connected to rail 19. A resistor 27 is connected across diode 26. A further resistor 28 and a capacitor 29 are connected in series across the diode 26. It will be appreciated that whenever the oscillator 14 is producing an oscillating signal, a positive voltage will collect on the capacitor 29, but this capacitor will discharge via resistors 27 and 28 when there is no oscillating signal being produced.
A comparator stage 30 is connected to detect the voltage on capacitor 29. This stage 30 includes an operational amplifier 31 with its inverting input connected to the junction of resistor 28 and capacitor 29. The non-inverting input of the amplifier 31 is connected to the junction of two resistors 32, 33 which are in series between a +ve supply rail 34 and the rail 1 9. The output of amplifier 31 goes high whenever there is an interruption in the oscillating signal from amplifier 1 8. The output of amplifier 31 is connected by a resistor 35 and a capacitor 36 in series to a rail 37 which is connected by a resistor 38 to an earth terminal 39.
A flip-flop memory circuit 40 is connected to the output of the comparator 30. This memory circuit 40 comprises two npn transistors 41,42 having their emitters connected to the rail 37. The collector of transistor 41 is connected by a resistor 43 and a light-emitting diode 44 in series to the rail 34, a resistor 45 being connected across the l.e.d. 44. Similarly resistors 46 and 48 and an led. 47 connect the collector of transistor 42 to the rail 34. The base of transistor 41 is connected by a resistor 49 to the junction of the resistor 35 and the capacitor 36 and is also connected by a resistor 50 by the collector of the transistor 42.The base of the transistor 41 is connected by a resistor 51 and a diode 52 in series to an initialising circuit including a capacitor 53 and a resistor 54 in series between the rails 34, 37 with a diode 55 connected across resistor 54, the anode of diode 52 being connected to the cathode of diode 55, the anode of which is connected to rail 37. A further resistor 56 connects the base of the transistor 42 to the collector of the transistor 41.
When the circuit is first switched on current initially flows through the capacitor 53 which biases transistor 42 on, so that it is this transistor which turns on hard as the circuit becomes active.
L.e.d. 47 is therefore illuminated initially (provided that oscillator 14 starts to oscillate). The memory circuit remains in this condition until the output of amplifier 31 goes high for a sufficient period to allow capacitor 36 to charge to a voltage high enough for the current in resistor 49 to start turning on the transistor 41. In this even transistor 41 turns on hard, transistor 42 turns off and only l.e.d. 44 is lift indicating a fault condition.
The resistor 35 and capacitor 36 prevent triggering of the memory circuit 40 by transients.
The voltage on rail 1 9 is derived from the
junction of two resistors 60,61 connected in
series between rail 34 and terminal 39, with a
smoothing capacitor 62 connected across the
resistor 61.
Turning now to the modification shown in
Figure 2 a more complex form of oscillator 114 is
shown which can be used in place of the oscillator
14 of Figure 1. This oscillator 114 includes an
operational amplifier 11 8 with its inverting input
connected to rail 11 9 by a resistor 120 and to its
output terminal by a resistor 121.The inductor 1 5
and capacitor 1 7 are connected, as before, in
parallel between the non-inverting input of
amplifier 11 8 and rail 11 9. A field effect transistor 1 70 is however connected with its drain-source
path in parallel with the inductor 1 5 and capacitor 1 7 so as to provide a variable resistor connected
across the tuned circuit 1 5, 1 7. A resistor 122
connects the tuned circuit 1 5, 1 7 to the amplifier
output.The gate of the f.e.t. 1 70 is connected by
a resistor 171 to the output terminal of an
operational amplifier 1 72 the non-inverting input of which is connected to the junction of two
resistors 173,174 between the rail 1 9 and a
reference voltage source (not shown) about +v below the voltage on rail 1 9. The inverting input of amplifier 1 72 is connected by a resistor 1 75 to the junction of two resistors 1 76, 177 which are in series between the output of amplifier 11 8 and the rail 1 9. A diode 1 78 has its anode connected to the junction of resistors 1 76, 1 77 and its cathode connected to the rail 1 9. Feedback around the amplifier 1 72 is provided by a resistor 1 79 and a capacitor 1 80 in parallel between the output of amplifier 1 72 and its inverting input. A capacitor 181 connects the gate of the f.e.t. 170 to the rail 19.
The values of the resistors 173,174,175 and 1 76 are chosen so that in a steady state with no oscillatory output from the amplifier the voltage at the output of the amplifier 1 72 is low enough to turn off the f.e.t. 1 70 completely so that the full output of the amplifier 11 8 is fed back via the resistor 122, i.e. in this condition the positive feedback round the amplifier 118 is at a maximum. When an oscillatory output is being produced the output of amplifier 172 will become less negative as the amplitude of the oscillating signal increases, thereby turning on f.e.t. which acts in the arrangement shown as a variable resistance. Thus the proportion of the amplifier 11 8 output fed back by the resistor 122 decreases as the amplitude increases and, in fact, the circuit stabilises with the f.e.t 1 70 set to an impedance such that stable oscillation is just occurring. When the tuned circuit 10 is juxtaposed to the inductor 15, with switch 1 3 open the oscillations stop, the time constant of resistor 171 with capacitor 181 being long (about 10 seconds) so that oscillation is not reestablished.
In the alternative oscillator shown in Figure 3 a circuit is shown in which an f.e.t. 270 is used to vary the gain of the operational amplifier 21 8 corresponding to amplifier 11 8 in Figure 2. The drain-source of the f.e.t. 270 is connected between the inverting input of amplifier 218 and the rail 1 9. A resistor 220 connects this inverting input to the output of amplifier 21 8. A resistor 222 connects the non-inverting input of amplifier 21 8 to the slider of a potentiometer 282 connected between the output terminal of amplifier 218 and the rail 19.A second potentiometer 283 is connected between the same points, and its slider is connected by a capacitor 284 to the cathode of a diode 285 the anode of which is connected to the gate of the f.e.t. 270. A resistor 286 and a capacitor 287 in parallel connect the gate of the f.e.t. to the rail 1 9.
As in the example described in Figure 2, the f.e.t.
impedance is automatically adjusted so that oscillation is just maintained in normal circumstances, the gain of amplifier 218 increases as the resistance of the f.e.t. decreases, which occurs when the amplitude of oscillation falls.
The circuits shown in Figures 2 and 3 does not need any adjustment when fitted to a vehicle to ensure that oscillation occurs when required.
In the above embodiments the inductors 11 and 1 5 are relatively small inductors mounted at positions spaced from the wheel axis so that they are magnetically coupled only briefly during each wheel rotation. In this case when the tyre pressure is low the oscillations are interrupted on each rotation of the wheel. In alternative embodiments (not shown), however, larger coils may be used which are arranged concentrically with the wheel. Thus the coils are always coupled magnetically. In this case when switch 1 3 is closed the oscillator produces oscillatory signals continuously, but when the tyre pressure falls and the switch 13 opens, the oscillator is inhibited continuously in the case of the example of Figure 1. In the examples shown in Figures 2 and 3 the oscillator will resume oscillation after an interval determined by components 171 and 181 or 286 and 287, but this interval is long enough to ensure that memory circuit 40 is set.
It will be appreciated that the l.e.d. 44 will light indicating a fault condition if the oscillator fails to oscillate as a result of a malfunction of the circuit.
The invention may also be applied to other electrical systems in which it is required to detect the state of an isolated switch, where it is required to maintain isolation between the switch and the detecting circuit. For example, the circuit described can be used to provide an input to a tractor vehicle control circuit in response to a switch on a trailer vehicle. The two inductors being incorporated in mating parts of a contactless connector.
Claims (26)
1. A circuit for detecting the condition of an isolated switch contact comprising the combination of a tuned circuit including an inductor, said switch contact being connected in parallel with said tuned circuit, an oscillator circuit including a further inductor arranged to be at least intermittently magnetically coupled to the inductor of the tuned circuit, such that when the switch contact is closed the oscillator circuit continuously produces an oscillatory output, whereas when said switch is open and the inductors are magnetically coupled, the tuned circuit absorbs oscillations of the oscillator circuit and prevents the oscillator circuit from producing said oscillatory output.
2. A circuit as claimed in claim 1 in which said oscillator comprises an amplifier having a resistive negative feedback path, and a positive feedback path shunted to "earth" by a further tuned circuit including said further inductor and a capacitor in parallel and tuned to the same resonant frequency as said first-mentioned tuned circuit.
3. A circuit as claimed in claim 2 in which said amplifier is an operational amplifier having a resistor connected between its output terminal and its inverting input terminal to define said negative feedback path, and also having a resistor connecting the output terminal to its noninverting input terminal and said further tuned circuit connected between the non-inverting input terminal and "earth".
4. A circuit as claimed in any one of claims 1 to 3 further comprising a detector circuit connected to the output of the oscillator and producing a d.c.
output whenever the oscillator produces an oscillating output.
5. A circuit as claimed in claim 4 further comprising a voltage comparator connected to the output of the detector and operating to compare the output of the detector with a reference voltage.
6. A circuit as claimed in claim 5 further comprising a flip-flop memory circuit biased initially to one of its stable states and arranged to be triggered to the other of its stable states by the output of the comparator when the oscillator ceases to produce an oscillating signal for a period of time of duration in excess of a predetermined limit.
7. A circuit as claimed in claim 3 further comprising a semiconductor variable impedance device connected across said further tuned circuit and a control circuit connected to control said device in accordance with the amplitude of the output of the operational amplifier, so as to decrease the impedance of said device as such amplitude increases.
8. A circuit as claimed in claim 7 in which said control circuit comprises a further operational amplifier having its inverting input connected by a resistor to the junction of two resistors which are in series between the output of the first
mentioned operational amplifier and "earth", a diode connected across one of said two resistors, a resistor and capacitor connected in parallel
between the output terminal of said further operational amplifier and the inverting input thereof, means applying a reference voltage to the
non-inverting input of said further operational amplifier, and a time constant circuit connecting the output of said further operational amplifier to a control terminal of the variable impedance device.
9. A circuit as claimed in claim 3 further comprising a semiconductor variable impedance device connected between the inverting input of said operational amplifier and "earth" and control means sensitive to the amplitude of the output of the oscillator for varying the impedance of said device so as to reduce such impedance as the amplitude increases.
10. A circuit as claimed in claim 9 in which said control means includes a resistor and a first capacitor in parallel between a control terminal of said device and "earth" and a diode and a further capacitor in series between the output of the operational amplifier and said control terminal, whereby the voltage on said first capacitor which determines the impedance of said device varies in accordance with said amplitude.
11. A vehicle tyre pressure monitoring system comprising a tuned circuit including an inductor, tyre pressure sensitive switch means connected in parallel with said tuned circuit and arranged to be closed when the associated tyre pressure is in excess of a predetermined level, said tuned circuit and said switch being mounted on a vehicle wheel assembly, an oscillator circuit also including an inductor mounted on a part of the vehicle such that the inductor of the oscillator circuit is magnetically coupled to the inductor of the tuned circuit at least periodically when the wheel is rotating, the arrangement being such that when the switch means is closed the oscillator circuit continuously produces an oscillatory output, whereas when said switch is open and the inductors are magnetically coupled, the tuned circuit absorbs oscillations of the oscillator circuit and prevents the oscillator circuit from producing said oscillatory signal.
12. A system as claimed in claim 11 in which said oscillator comprises an amplifier having a resistive negative feedback path, and a positive feedback path shunted to "earth" by a further tuned circuit including said further inductor and a
capacitor in parallel and tuned to the same
resonant frequency as said first-mentioned tuned
circuit.
13. A system as claimed in claim 12 in which
said amplifier is an operational amplifier having a
resistor connected between its output terminal
and its inverting input terminal to define said
negative feedback path, and also having a resistor
connecting the output terminal to its non
inverting input terminal and said further tuned
circuit connected between the non-inverting input
terminal and "earth".
14. A system as claimed in claims 11 to 13
further comprising a detector circuit connected to
the output of the oscillator and producing a d.c.
output whenever the oscillator produces an
oscillating output.
1 5. A system as claimed in claim 14 further
comprising a voltage comparator connected to the output of the detector and operating to compare the output of the detector with a reference voltage.
16. A system as claimed in claim 15 further comprising a flip-flop memory circuit biased initially to one of its stable states and arranged to be triggered to the other of its stable states by the output of the comparator when the oscillator ceases to produce an oscillating signal for a period of time of duration in excess of a predetermined limit.
17. A system as claimed in claim 13 further comprising a semiconductor variable impedance device connected across said further tuned circuit and a control circuit connected to control said device in accordance with the amplitude of the output of the operational amplifier, so as to decrease the impedance of said device as such amplitude increases.
18. A system as claimed in claim 17 in which said control circuit comprises a further operational amplifier having its inverting input connected by a resistor to the junction of two resistors which are in series between the output of the first-mentioned operational amplifier and "earth", a diode connected across one of said two resistors, a resistor and capacitor connected in parallel between the output terminal of said further operational amplifier and the inverting input thereof, means applying a reference voltage to the non-inverting input of said further operational amplifier, and a time constant circuit connecting the output of said further operational amplifier to a control terminal of the variable impedance device.
19. A system as claimed in claim 1 3 further comprising a semiconductor variable impedance device connected between the inverting input of said operational amplifier and "earth" and control means sensitive to the amplitude of the output of the oscillator for varying the impedance of said device so as to reduce such impedance as the amplitude increases.
20. A system as claimed in claim 19 in which said control means includes a resistor and a first capacitor in parallel between a control terminal of said device and "earth" and a diode and a further capacitor in series between the output of the operational amplifier and said control terminal, whereby the voltage on said first capacitor which determines the impedance of said device varies in accordance with said amplitude.
21. A circuit for detecting the condition of an
isolated switch contact substantially as
herein before described with reference to Figure 1
of the accompanying drawings.
22. A circuit for detecting the condition of an
isolated switch contact substantially as
hereinbefore described with reference to Figure 1
as modified by Figure 2 of the accompanying
drawings.
23. A circuit for detecting the condition of an
isolated switch contact substantially as
hereinbefore described with reference to Figure 1 as modified by Figure 3 of the accompanying drawings.
24. A vehicle tyre pressure monitoring system substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.
25. A vehicle tyre pressure monitoring system substantially as hereinbefore described with reference to Figure 1 as modified by Figure 2 of the accompanying drawings.
26. A vehicle tyre pressure monitoring system substantially as hereinbefore described with reference to Figure 1 as modified by Figure 3 oF the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8027534A GB2058420B (en) | 1979-09-13 | 1980-08-26 | Circuit for use in the detection of the condition of an isolated switch contact |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7931818 | 1979-09-13 | ||
| GB8027534A GB2058420B (en) | 1979-09-13 | 1980-08-26 | Circuit for use in the detection of the condition of an isolated switch contact |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2058420A true GB2058420A (en) | 1981-04-08 |
| GB2058420B GB2058420B (en) | 1984-05-02 |
Family
ID=26272869
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8027534A Expired GB2058420B (en) | 1979-09-13 | 1980-08-26 | Circuit for use in the detection of the condition of an isolated switch contact |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2058420B (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2149951A (en) * | 1983-11-12 | 1985-06-19 | Michael Sacks | Security checking systems |
| GB2337335A (en) * | 1998-05-15 | 1999-11-17 | Algonquin Scient Llc | Tire pressure sensing system |
| US6335690B1 (en) | 1997-01-15 | 2002-01-01 | Algonquin Scientific, Llc | Fluid sensing system |
| US6362732B1 (en) | 1997-01-15 | 2002-03-26 | Algonquin Scientific Llc | Tire pressure sensing system |
| US6756892B2 (en) | 1997-01-15 | 2004-06-29 | Algonquin Scientific, Llc | Tire pressure sensing system |
-
1980
- 1980-08-26 GB GB8027534A patent/GB2058420B/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2149951A (en) * | 1983-11-12 | 1985-06-19 | Michael Sacks | Security checking systems |
| US6124787A (en) * | 1997-01-15 | 2000-09-26 | Algonquin Scientific, Llc | Tire pressure sensing system |
| US6335690B1 (en) | 1997-01-15 | 2002-01-01 | Algonquin Scientific, Llc | Fluid sensing system |
| US6362732B1 (en) | 1997-01-15 | 2002-03-26 | Algonquin Scientific Llc | Tire pressure sensing system |
| US6756892B2 (en) | 1997-01-15 | 2004-06-29 | Algonquin Scientific, Llc | Tire pressure sensing system |
| GB2337335A (en) * | 1998-05-15 | 1999-11-17 | Algonquin Scient Llc | Tire pressure sensing system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2058420B (en) | 1984-05-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |