RF identification system for providing static data and one bit of variable data representative of an external stimulus

• US 5,764,138 A
• Filed: 04/29/1994
• Issued: 06/09/1998
• Est. Priority Date: 04/29/1994
• Status: Expired due to Term

• Current Assignee: Assa Abloy AB
• Original Assignee: HID Corporation (Assa Abloy AB)
• Inventors: Lowe, Peter R.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): Wu, Daniel J.
• Application Number:
  US08/235,073
• Time in Patent Office: 1,502 Days
• Field of Search: 340/442, 340/445, 340/447, 340/572, 340/573, 340/825.54, 340/825.69, 340/825.72, 73/146.2, 73/146.8, 200/61.22, 342/51
• US Class Current: 340/447
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
• CPC Class Codes: B60C 23/0433 Radio signals
• CPC Class Codes: B60C 23/0442 the transmitted signal comprises further information, e.g. instruction codes, sensor characteristics or identification data
• CPC Class Codes: G06K 19/07764 the adhering arrangement making the record carrier attachable to a tire tire temperature or pressur control arrangements, see B60C23/00

Abstract

An RF identification system for generating data indicative of an item that is tagged, and one bit of variable data representative of an external stimulus. An ID code reader is provided and an RF identification tag is coupled to the item that is to be monitored and the ID code reader queries the tag. The tag comprises two RF transponder chips that store a data relating to the item, and an excitation coil coupled thereto. A switch is coupled to the chips and excitation coil, and a capacitor is coupled across the switch. A sensor is coupled to the switch for generating one bit of variable data representative of an external stimulus, such as the pressure in a tire. The ID code reader comprises an exciter and RF excitation coil, and a receiver and an RF receiver coil. The receiver includes phase detection circuitry for detecting a state of the switch by detecting the phase shift between signals received from each of the transponder chips. When the switch is shorted, the effect of the capacitor is nullified. When the switch is is open, then the return signal from the second transponder chip has a small phase shift with respect to the signal from the first transponder chip. The phase detection circuitry detects this phase shift and determines the state of the switch. The system permits the use of an RF identification tag in remote or inaccessible positions to determine the state of a variable (the position of the switch) and store identification data. An example of this is an identification tag in a vehicle tire that stores the tire ID and also enables the reading of a pressure switch to confirm adequate tire pressure.

Claims

1. An RF identification system for generating data indicative of an item that is tagged, and one bit of variable data representative of an external stimulus, said system comprising:

an RF identification tag coupled to the item that is to be monitored that comprises;

first and second RF transponder chips that each store data relating to the item that is to be monitored and that each comprise first and second antenna outputs;

an excitation coil having one input coupled to respective first antenna outputs of the first and second RF transponder chips;

a switch coupled between respective second antenna outputs of the first and second RF transponder chips and coupled to a second input of the excitation coil;

a capacitor coupled across the switch; and

a sensor coupled to the switch for generating one bit of variable data representative of an external stimulus; and

an ID code reader that comprises;

an exciter;

an RF excitation coil coupled to the exciter;

a receiver comprising an RF receiver coil and phase detection circuitry for detecting a state of the switch by detecting the phase shift between signals received from each of the transponder chips.

2. The RF identification system of claim 1 wherein the item comprises a tire.

3. The RF identification system of claim 1 wherein the sensor comprises a pressure sensor.

4. The RF identification system of claim 3 wherein the item comprises a tire.

5. The RF identification system of claim 2 wherein the one bit of variable data representative of the external stimulus is representative of the pressure in the tire.

6. The RF identification system of claim 4 wherein the one bit of variable data representative of the external stimulus is representative of the pressure in the tire.

7. In an RF identification system that comprises an RF identification tag coupled to the item that is to be monitored for generating data indicative of the item, and an ID code reader comprising an exciter, an RF excitation coil coupled to the exciter, and a receiver comprising an RF receiver coil and phase detection circuitry for detecting a state of the switch by detecting the phase shift between signals received from identification tag, wherein the improvement comprises an RF identification tag for generating the data indicative of the item, and one bit of variable data representative of an external stimulus, said identification tag comprising:

first and second RF transponder chips that each store data relating to the item that is to be monitored and that each comprise first and second antenna outputs;

an excitation coil having one input coupled to respective first antenna outputs of the first and second RF transponder chips;

a switch coupled between respective second antenna outputs of the first and second RF transponder chips and coupled to a second input of the excitation coil;

a capacitor coupled across the switch; and

a sensor coupled to the switch for generating one bit of variable data representative of the external stimulus.

8. The RF identification system of claim 7 wherein the item comprises a tire.

9. The RF identification system of claim 7 wherein the sensor comprises a pressure sensor.

10. The RF identification system of claim 9 wherein the item comprises a tire.

11. The RF identification system of claim 8 wherein the one bit of variable data representative of the external stimulus is representative of the pressure in the tire.

12. The RF identification system of claim 10 wherein the one bit of variable data representative of the external stimulus is representative of the pressure in the tire.