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Claims  |
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What is claimed is:
1. A system for monitoring and affecting actions on behalf of a group of objects, comprising:
a first electronic tag attached to an object in the group, comprising:
circuitry for communicating with a second tag, the circuitry communicating at least information pertaining to an object in the group, and
a memory connected to the circuitry and capable of storing the information, and
a second electronic tag attached to an object in the group, comprising
circuitry for communicating the information with the first tag,
a memory connected to the circuitry in the second tag and capable of storing the information,
wherein the information comprises a distance between the first tag and the second tag.
2. The system of claim 1, wherein the first tag comprises a time measuring device connected to a controller for measuring a time duration required for a signal to travel between the first tag and the second tag.
3. The system of claim 2, wherein
the time measuring device in the first tag comprises a clocked counter which has a first count corresponding to the time of transmission of the signal and which subsequently has a second count corresponding to the time of recognition that said
signal has been received; and
said device uses the product of the clock period and the difference between said counts to determine the time duration.
4. The system of claim 3, wherein the clock counter starts in response to the transmission of the signal and stops in response to the reception of said signal.
5. The system of claim 3, wherein the memory in the first tag includes a program configuring the controller in the first tag to execute a function when the controller reads the memory, the function causing the controller to determine the
distance based on the time duration.
6. The system of claim 5, wherein the second tag further comprises a second counter connected to the controller in the second tag, the counter in the first tag further comprising a mechanism for adjusting a frequency of the first-mentioned
counter, the mechanism being coupled to the controller in the first tag, the program in the first tag causing the controller in the first tag to employ the mechanism to offset the frequency of the first-mentioned counter from a frequency of the counter
in the second tag.
7. The system of claim 6 wherein the program in the first tag configures the controller to adjust the frequency of the counter in the first tag based on the distance.
8. The system of claim 7 wherein the program in the first tag causes the controller in the first tag to perform in a specified and predetermined manner the functions of:
adjusting the frequency of the counter in the first tag based on the frequency of the counter in the second tag, and
enabling the circuitry in the first tag to transmit a number of symbols at an intersymbol period related to the frequency of the counter in the first tag.
9. The system of claim 8 wherein the program in the first tag further causes the controller in the first tag to perform the function of selecting the number of symbols and the frequency of the counter in the first tag such that a number of clock
cycles of the first tag during a transmission and receipt of the symbols is substantially equal to a number of clock cycles of the clock of the second tag within an offset (n), n and the number of symbols having no common factors other than one.
10. The system of claim 2, wherein the second tag further comprises a delay circuit connected between the circuitry and the controller in the second tag, the delay circuit causing the second tag to delay returning the signal to the first tag by
a given time period.
11. A method of measuring a distance between two objects, said method comprising the steps of:
transmitting from one of said objects a plurality of symbols, said transmissions occurring in a first series in which consecutive transmissions are separated by a first time interval which is a multiple of a first clock period;
receiving each of said symbols at the other of said objects and re-transmitting each of said symbols back to said one of said objects, said re-transmissions occurring in a second series in which consecutive re-transmissions are separated by a
second time interval which is different from the first time interval and which is a multiple of a second clock period which is different from the first clock period;
measuring a round-trip time corresponding to detection of receipt from said other of said objects of each of said symbols, each said round-trip time being a multiple of said first clock period; and
determining said distance between said objects using a velocity of said symbols, said clock periods, at least one of said time intervals, and said round-trip times.
12. The method of claim 11, wherein
one clock period is approximately equal to the product of said other clock period and a fraction;
the numerator of said fraction is equal to the sum of two terms;
the first term of said sum is the product of the number of symbols transmitted and the number of first clock periods corresponding to the first time interval;
the second term of said sum is a whole number that shares no multiplicative factors, other than 1, with said number of symbols transmitted; and
the denominator of said fraction is equal to the product of the number of symbols transmitted and said number of first clock periods corresponding to said first time interval.
13. The method of claim 11, wherein the measured round-trip times vary and have a variation range equal to one first clock period.
14. A method of measuring a distance between two objects, said method comprising the steps of:
transmitting from one of said objects a plurality of symbols, said transmissions occurring in a series in which consecutive transmissions are separated by a time interval which is a multiple of a first clock period;
returning each of said symbols from the other of said objects back to said one of said objects;
measuring a round-trip time corresponding to detection of receipt from said other of said objects of each of said symbols, each said round-trip time corresponding to a multiple of a second clock period; and
determining said distance between said objects using a velocity of said symbols, said clock periods, at least one of said time intervals, and said round-trip times.
15. The method of claim 14, further comprising a step of detecting each transmission using the second clock period, wherein the round-trip times correspond to time intervals between detections of receipt and transmission of the symbols.
16. The method of claim 14, wherein one of the clock periods is approximately equal to the product of the other clock period and a fraction;
the numerator of said fraction is equal to the sum of two terms;
the first term of said sum is the product of the number of symbols transmitted and the number of first clock periods corresponding to the first time interval;
the second term of said sum is a whole number that shares no multiplicative factors, other than 1, with said number of symbols transmitted; and
the denominator of said fraction is equal to the product of the number of symbols transmitted and said number of first clock periods corresponding to said first time interval.
17. The method of claim 14, wherein the measured round-trip times vary and have a variation range equal to one first clock period.
18. A method of measuring a distance between two objects, said method comprising the steps of:
transmitting from one of said objects a first symbol;
transmitting from said one of said objects a second symbol, said transmission of said second symbol being separated from said transmission of said first symbol by a time interval which is a multiple of a first clock period;
receiving said first symbol at the other of said objects and re-transmitting said first symbol back to said one of said objects;
receiving said second symbol at said other of said objects and re-transmitting said second symbol back to said one of said objects, said re-transmission of said second symbol being separated from said re-transmission of said first symbol by a
second time interval which is a multiple of a second different clock period;
measuring a first round-trip time corresponding to detection of receipt from said other of said objects of said first symbol, said first round-trip time being a multiple of said first clock period;
measuring a second round-trip time corresponding to detection of receipt from said other of said objects of said second symbol, said second round-trip time being a multiple of said first clock period;
if said round-trip times are not different by at least one first clock period, repeating said transmitting, said receiving, said re-transmitting, and said round-trip measuring of said second symbol until said round-trip times are different by one
first clock period; and
determining the distance between said objects using a velocity of the symbols, the clock periods, the time intervals, and the round-trip times.
19. The method of claim 18, wherein the first and second round-trip times are original round-trip times, said original round-trip times being different by one first clock period, said method further comprising the steps of
(a) equating the clock periods;
(b) temporarily changing one of said clock periods for a period of time equal to a fraction of the time interval;
(c) determining a new round-trip time for a symbol;
(d) comparing said new round-trip time to at least one of said original round-trip times; and
repeating (a) through (d) for a plurality of iterations, said fraction being different for each iteration.
20. A method of measuring a distance between two objects, one of said objects being able to measure time with a resolution of a minimum period of time, said method comprising the steps of:
transmitting a plurality of symbols from said one of said objects;
receiving each of said symbols at the other of said objects and re-transmitting each of said symbols back to said one of said objects after a delay period, said delay period being different for each symbol and being a multiple of a constant delay
unit, said delay unit being approximately equal to said minimum period divided by the number of symbols transmitted;
measuring a round-trip time corresponding to detection of receipt of each said symbol from said other of said objects, each round-trip time corresponding to a multiple of said minimum period; and
determining said distance between said objects using a velocity of said symbols, said minimum period, and at least one of said round-trip times.
21. A method of measuring a distance between two objects, one of said objects being able to measure time with a resolution of a minimum period of time, said method comprising the steps of:
transmitting a plurality of symbols from said one of said objects;
after a first delay period, detecting each transmission, said first delay period being different for each transmission and being a multiple of a constant delay unit, said delay unit being approximately equal to said minimum period divided by the
number of symbols transmitted;
returning each of said symbols at the other of said objects back to said one of said objects;
after a second delay period, detecting the receipt of each of said symbols from said other of said objects, said second delay period being different for each receipt and being a multiple of said delay unit;
measuring a time difference between detections of transmission and receipt of each of said symbols, each said time difference being a multiple of said minimum period; and
determining said distance between said objects using a velocity of said symbols, said minimum period, and said time differences.
22. A method of measuring a distance between two objects, one of said objects being able to measure time with a resolution of a minimum period of time, said method comprising the steps of:
transmitting a first symbol from said one of said objects;
receiving said first symbol at the other of said objects and re-transmitting said first symbol back to said one of said objects;
measuring a first round-trip time corresponding to detection of receipt from said other of said objects of the first symbol, said first round-trip time being a multiple of said minimum period;
a) transmitting another symbol from said one of said objects;
b) receiving said another symbol at said other of said objects and re-transmitting said another symbol back to said one of said objects after a delay period, said delay period being a multiple of a delay unit, said delay unit being approximately
equal to a fraction of said minimum period, the number of delay units in said delay period being equal to the number of symbols previously retransmitted;
c) measuring another round-trip time corresponding to detection of receipt from said other of said objects of said another symbol, said another round-trip time being a multiple of said minimum period;
if said first round-trip time and said another round-trip time are equal, repeating a) through c) until said round-trip times are different by one said minimum period; and
determining said distance between said objects by using a velocity of said symbols, said minimum period, delay unit, and said round-trip times.
23. The method of claim 22, further comprising reducing the delay unit to a smaller fraction of the minimum period and repeating a) through c).
24. Apparatus for measuring a distance between two objects, said apparatus comprising
a transmitter having a first clock for transmitting from one of said objects a plurality of symbols, said transmissions occurring in a first series in which consecutive transmissions are separated by a first time interval which is a multiple of
the period of said first clock;
a transponder having a second clock for receiving each of said symbols at the other of said objects and re-transmitting each of said symbols back to said one of said objects, said re-transmissions occurring in a second series in which consecutive
re-transmissions are separated by a second time interval which is different from said first time interval and which is a multiple of said second clock's period which is different from the period of said first clock;
a clock counter for measuring each round-trip time corresponding to detection of receipt from said other of said objects of each of said symbols, each round-trip time being a multiple of said first clock period; and
a calculator for determining said distance between said objects using a velocity of said symbols, said clock periods, at least one of said time intervals, and said round-trip times.
25. Apparatus for measuring a distance between two objects, said apparatus comprising:
a transmitter having a first clock for transmitting from one of said objects a plurality of symbols, said transmissions occurring in a series in which consecutive transmissions are separated by a time interval which is a multiple of the period of
said first clock;
a transponder for returning each of said symbols from the other of said objects back to said one of said objects;
a counter having a second clock for measuring a round-trip time corresponding to detection of receipt from said other of said objects of each of said symbols, each said round-trip time corresponding to a multiple of the period of said second
clock; and
a calculator for determining said distance between said objects using a velocity of said symbols, said clock periods, said time interval, and said round-trip times.
26. Apparatus for measuring a distance between two objects, said apparatus comprising:
a transmitter for transmitting from one of said objects a first symbol and transmitting from said one of said objects a second symbol, said transmission of said second symbol being separated from said transmission of said first symbol by a time
interval which is a multiple of a first clock period;
a transponder for (a) receiving said first symbol at the other of said objects and re-transmitting said first symbol back to said one of said objects and (b) receiving said second symbol at said other of said objects and re-transmitting said
second symbol back to said one of said objects, said re-transmission of said second symbol being separated from said re-transmission of said first symbol by a second time interval which is a multiple of a second different clock period;
a clock counter for (a) measuring a first round-trip time corresponding to detection of receipt from said other of said objects of said first symbol, said first round-trip time being a multiple of said first clock period, and (b) measuring a
second round-trip time corresponding to detection of receipt from said other of said objects of said second symbol, said second round-trip time being a multiple of said first clock period;
a comparator for (a) testing if said round-trip times are not different by one first clock period, and (b) initiating repeating of said transmitting, said receiving, said re-transmitting, and said round-trip measuring of said second symbol until
said round-trips are different by one first clock period; and
a calculator for determining the distance between said objects using a velocity of the symbols, the clock periods, the time intervals, and the round-trip times.
27. A method of measuring a distance between two objects, said method comprising the steps of:
transmitting from one of said objects a plurality of symbols, said transmissions occurring in a first series in which consecutive transmissions are separated by a first time interval which is a multiple of a first clock period, said symbols
having a constant velocity;
receiving each of said symbols at the other of said objects and re-transmitting each of said symbols back to said one of said objects, said re-transmissions occurring in a second series in which consecutive re-transmissions are separated by a
second time interval, said second time interval being different from the first time interval, said second time interval being a multiple of a second clock period which is different from the first clock period, each said re-transmission thus occurring
after a delay, said delay being different for each re-transmission and constituting the period of time between arrival of each said symbol at said other of said objects and re-transmission of each said symbol, said delay having a nominal length which is
a multiple of a delay unit, said delay unit being equal to the product of the number of first clock periods corresponding to the first time interval and the difference between the clock periods, said delay unit also being equal to the second clock period
divided by the number of symbols in the plurality of symbols, said delay having an actual length which is within one delay unit of said nominal length;
measuring a round-trip time corresponding to detection of receipt from said other of said objects of each of said symbols, each said round-trip time being a multiple of said first clock period; and
determining said distance between said objects by multiplying said velocity of said symbols by half of the difference between the average of all of said round-trip times and the first clock period.
28. The method of claim 27, wherein
the delay further comprises an extra delay which is a multiple of said second clock period; and
the distance is determined by multiplying said velocity by half of the difference between (a) the average of all of said round-trip times and (b) the sum of said extra delay and the first clock period.
29. A method of measuring a distance between two objects, said method comprising the steps of:
transmitting from one of said objects a plurality of symbols, said transmissions occurring in a series in which consecutive transmissions are separated by a time interval which is a multiple of a first clock period, said symbols having a constant
velocity;
detecting said transmissions using a second clock period, said second clock period being different from said first clock period, each said transmission detection thus occurring after a delay, said delay being different for each said detection and
constituting the period of time between each said transmission and said detection of each said transmission, said delay having a nominal length which is a multiple of a delay unit, said delay unit being equal to the product of the number of first clock
periods corresponding to the time interval and the difference between the clock periods, said delay unit also being equal to the second clock period divided by the number of symbols in the plurality of symbols, said delay having an actual length which is
within one delay unit of said nominal length;
returning each of said symbols from the other of said objects back to said one of said objects;
detecting the arrivals of said returning symbols back at said one of said objects using said second clock period, each said arrival detection thus occurring after a second delay, said second delay being different for each said detection and
constituting the period of time between each said arrival and said detection of each said arrival, the nominal length of said second delay being a multiple of said delay unit, said second delay having an actual length which is within one delay unit of
said nominal length of said second delay;
measuring a round-trip time corresponding to detection of receipt from said other of said objects of each of said symbols, each said round-trip time corresponding to a multiple of a second clock period; and
determining said distance between said objects by multiplying said velocity by half of the average of the round-trip times.
30. The method of claim 29, wherein
the symbols are returned from the other of said objects after an extra delay; and
the distance is determined by multiplying said velocity by half of the difference between the average of all of the round-trip times and said extra delay.
31. The method of claim 27, further comprising a step of offsetting the average of the round-trip times, wherein the offset is an amount of time equal to the second clock period divided by twice the product of (a) the number of symbols and (b)
the number of first clock periods corresponding to the first time interval. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to managing assets equipped with active electronic tags.
Asset management systems attempt to monitor the existence, location and status of items being transported or stored. The systems include two main types: barrier systems and continuous systems.
Barrier systems determine whether an asset is located within a cell delimited by a set of stationary interrogators. The interrogators detect the asset as it crosses a boundary of the cell, but are incapable of determining a position of the asset
within the cell.
Typical barrier systems fix a bar code to each asset, and use bar code readers as interrogators. Examples include systems used by car factories and mail carriers, such as Federal Express and United Parcel Service.
Another type of barrier system attaches a transponder to each asset and uses radio transceivers as interrogators. The transponders are passive, that is, they respond when activated by an interrogator but are incapable of initiating
communications or other functions. An example includes a railroad system developed by AMTECH, in which each railroad car on a train is equipped with a transponder. Interrogators include transceivers that are placed along a railway.
Continuous systems determine the position of an asset anywhere within a monitoring area. An example, implemented by LOJACK, equips cars with an active transponder. The transponder is active because it initiates its own functions, for example,
it monitors a particular hailing frequency. If the car is stolen, LOJACK uses special transmitters to establish communication with the transponder at the hailing frequency. Receivers provided to police cars analyze the communications to locate the car.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention features a method for monitoring an object in a moving vehicle by attaching an electronic tag to the object. An electronic device detects the presence of the object by communicating with the tag while the
object is being moved by the vehicle.
Preferred embodiments of this aspect of the invention include the following features.
The absence of the object is reported to a user or a computer accessible to the user when the device is unable to communicate with the tag. The absence may be reported periodically to either an owner of the object or a possessor of the object.
A location of the object is determined by establishing communications between the tag and a sensor storing location information. The location of the object is compared to a planned route, and any discrepancy between the location and the planned
route is reported to the user. The discrepancy may be reported through a computer. The user determines a new route for the object and notifies the elective device of the new route. The user may determine the new route using a computer.
The object may be disposed in a container to which is attached an electronic tag. Communication is established between the tag on the object and the tag on the container. The tag on the object communicates with the electronic device through the
tag on the container. The container may also be placed in a second container to which is attached an electronic tag. The tag on the first container communicates with the tag on the second container.
Each tag stores a unique identification for the object, a description of the object, the object's shipper and destination and a signature of each possessor of the object. The signatures stored by the tag are forwarded to the electronic device
when the tag reaches the limit of its memory capacity or when the object to which the tag is attached reaches the end of its monitoring period. The signatures are then deleted from the tag memory.
In general, in another aspect, the invention features a system for monitoring and affecting actions on behalf of a group of objects. A first electronic tag attached to an object includes circuitry for communicating with a second electronics tag,
the circuitry communicating at least information pertaining to an object in the group. The first tag also includes a memory connected to the circuitry and capable of storing the information. The second electronic tag attached to another object includes
circuitry for communicating with the first tag and a memory connected in an analogous manner.
Preferred embodiments of this aspect of the invention include the following features.
The first and second tags each include a controller connected to the memory and the communication circuitry. The information communicated between the tags includes a distance between the tags. The first tag has a time measuring device connected
to the controller, the device measuring a time duration required for a signal to travel between the first tag and the second tag. The device in the first tag includes a clocked counter which has a first count corresponding to the time of transmission of
the signal and which subsequently has a second count corresponding to the time of recognition that the signal has been received. The device uses the product of the clock period and the difference between the counts to determine the time duration.
The second tag may also include a delay circuit connected between the circuitry and the controller, the delay circuit causing the second tag to delay returning the signal to the first tag by a given time period. The memory in the first tag
includes a program causing the controller to execute a function when the controller reads the memory, the function causing the controller to determine the distance based on the time duration.
The second tag includes a second counter connected to the controller in the second tag. The counter in the first tag has a mechanism for adjusting a frequency of the first-mentioned counter, the mechanism being coupled to the controller in the
first tag. The program in the first tag causes the controller to employ the mechanism to offset the frequency of the first-mentioned counter from a frequency of the counter in the second tag based on the frequency of the counter in the second tag.
The program in the memory of the first tag also causes the controller to enable the circuitry in the first tag to transmit a number of symbols at an intersymbol period such that a number of clock cycles of the first tag during a transmission and
receipt of the symbols is substantially equal to a number of clock cycles of the clock of the second tag within an offset (n), where n and the number of symbols have no common factors other than one.
The first tag further includes a power source coupled to the controller and supplying power to the circuitry in the first tag. The program in the memory of the first tag causes the controller to adjust the power supplied to the controller to
that minimal level which allows communication between the circuitry in the first tag and the circuitry in the second tag.
The system also includes a set of tags neighboring the first tag and including the second tag. A program in the memory of the first tag causes the controller to identify the set of tags by enabling the circuitry in the first tag to establish
communications with each tag in the set. The controller determines the distance between each pair of tags in the set and the relative locations of each tag in the set based on the distances. The controller then selects a particular tag located on the
periphery of the set for communicating outside the set.
In some embodiments, the information communicated between the tags includes a distance of the first tag from three different tags in the set and the absolute locations of the three different tags. The absolute locations may be derived from a
sensor communicating its location to one of the three different tags. A program in the memory of the first tag causes the controller to determine the absolute position of the first tag from the information. The controller also minimizes an error in the
absolute position of the first tag.
A program in the memory of the first tag also causes the controller to enable the circuitry in the first tag to communicate information with each tag in the set and analyze the information from the circuitry to determine the presence of a new tag
in the set. The controller then causes the circuitry to communicate with the new tag to obtain a distance between the first tag and the new tag and a location of the new tag. The controller refines the absolute position of the first tag based on the
location of the new tag and the distance between the first tag and the new tag.
In some embodiments, the information communicated by the tags includes the distance of the first tag from the second tag at a number of different times, and the absolute locations of the second tag at each of the times. A program in the memory
of the first tag causes the controller to determine the absolute position of the first tag from the information.
A program in the memory of the first tag causes the controller to select tags in the set as relay tags, the circuitry in the relay tags being designated to route messages between a pair of tags in the set. The relay tags provide communications
between each pair of tags in the set with a minimum number of communication links. The controller performs a Delaunay triangulation to determine a topology of the tags in the set and selects the relay tags based on the topology.
In some embodiments, the system includes a user-operated device for communicating with the circuitry in the first tag. The information communicated between tags includes an identity of a tag in the set capable of long range communication and a
change in an identity of a tag in the set. The program in the memory of the first tag configures the controller to enable the circuitry in the first tag to notify the device of the change in the identity of a tag in the set.
A program in the memory of the first tag also causes the controller to divide the set of tags into subsets when a number of tags in the set increases above a threshold value. The memory in the first tag further stores an identification code for
the first tag, and the program causes the controller to truncate the code and employ the circuitry in the first tag to communicate the truncated code to a second tag within a subset to minimize energy consumption.
The information communicated between tags may also include an identification of a tag belonging to a different set. A program in the memory of the first tag causes the controller to merge the first-mentioned set with the different set when a
number of tags in the first-mentioned set falls below a selected threshold value.
The system may also include a time sensor which communicates a time to the circuitry in the second tag. The controller enables the circuitry in the first tag to communicate with the second tag to obtain the time, and sets the counter in the
first tag using the communicated time.
A sensor may also communicate location information to the first tag, and the memory in the second tag may store a transportation route for the object attached to the first tag. The controller employs the circuitry in the first tag to query the
second tag regarding the transportation route and to query the sensor regarding the tag's location. The controller then derives a present time from the counter in the first tag, determines an expected position of the object at the present time based on
the route and an actual position of the object based on the location. The tag then decides whether the actual position deviates from the expected position. The controller notifies the user-operated device of a deviation from the expected position by
causing the circuitry to communicate with the device.
The user-operated device includes a processor connected to a device communication circuitry. A device memory is coupled to the processor and includes a program configuring the processor to perform a called-for function when the processor reads
the device memory. The function can cause the processor to determine a new route for the object attached to the first tag based on the deviation, and causes the processor to employ the device communication circuitry to communicate the new route to the
first tag. The processor also employs the device communication circuitry to receive communications indicating a change in the route from at least one of the following: a second device, a tag and a system operator.
In some embodiments, the first tag has a detector connected to the controller. The detector notifies the controller when the first tag is detached from the object to which it had been attached. The controller enables the circuitry in the first
tag to notify the user-operated device in response to notification from the detector that the first tag is detached from the object.
The circuitry in the first tag includes ports for infrared, radio frequency and acoustic communications. The port for radio frequency communications includes circuitry for communicating over a number of channels. A program in the memory causes
the controller to select one channel for RF communication over the port and to code the information with an encryption code before enabling the tag's circuitry to communicate the information to the second tag.
The first tag can also include a power source connected to the controller and a timer connected to both the power source and controller. The controller loads a time period in the timer, and the timer causes the power from the power source to be
removed from the controller and restored after the time period elapses.
A detector connected to the controller and the power source provides a detection signal to the controller indicating whether the power source has deteriorated beyond a threshold level. Another detector connected to the controller provides a
detection signal to the controller indicating whether the tag has been tampered with. This detector includes a transmitter, a receiver, and an optical fiber connecting an output of the transmitter to an input of the receiver. The transmitter forwards a
signal over the optical fiber to the input of the receiver. The receiver notifies the controller if the signal does not arrive at the input of the receiver.
The system may also include a sensor detecting the condition of an object and communicating the condition to the circuitry in the first tag. The circuitry in the first tag subsequently communicates the condition to the second tag. The memory in
the first tag includes a stored set of thresholds values related to the condition, each threshold being associated with a time. | | |
