A data transmission device (11; 111,) for use in a system (10) comprising a plurality of such devices is described along with a corresponding method of data transmission. A data signal (at 23) is provided for transmission and a timer apparatus (16, 18; 16, 118, 160) establishes a sequence of maximum time intervals (6 hours; 6 hours and 20 seconds) during which the data signal can be transmitted. A transmitter (18, 24, 25; 118, 24, 25) transmits the data signal during each of these maximum time intervals. The timer apparatus (16, 18; 16, 118, 160) generates a random number (steps 33, 54; steps 172, 195) for each one of the maximum time intervals, and the transmitter (18, 24, 25; 118, 24, 25) determines the transmission times for the data signal in accordance with the random numbers provided for each of these maximum time intervals. Preferably, the data transmission devices are part of a data transmission system (10) which includes a data receiver (12), and the data signal is obtained from and corresponds to the output of a utility meter (13). By utilization of random numbers to randomize the transmit times of the transmission devices, the probability that data transmissions from one transmission device will interfere with data transmissions from another device is substantially minimized.
This is a continuation of application Ser. No. 07/997,390filed De. 28, 1992 and now abandoned.
FIELD OF THE INVENTION
The present invention relates to the field of data transmission devices, systems utilizing such devices and methods for implementing data transmission. More particularly, the present invention has applicability to independently operative utility meter reading devices which transmit utility meter readings to a central data receiver location, preferably by wireless radiation communications.
BACKGROUND OF THE INVENTION
Utility meter reading systems have been proposed in which a utility meter reading device is provided in conjunction with each utility meter. In some of these meter systems the reading devices comprise data transmission devices which transmit utility meter reading data to a central meter reading location. Such central reading systems allow the remote reading of utility meters without requiring the physical reading of individual meters at their locations by meter reading persons. In other words, such systems eliminate the need for a meter reader person visiting each and every meter location in order to read the meters. By "utility meters" what is meant is a meter which measures the use of a commercial or residential utility resource, such as electricity, gas, water, etc.
In systems which provide for the remote reading of a plurality of utility meters, one problem that may occur is that several meters may attempt to transmit their data to the same central location at the same time. This can result in data collisions and destruction of meter reading data such that an accurate reading of the meters may not be obtained. Some systems have proposed periodic transmission of meter data by each individual meter to cut down on data transmit time by each device, but, the data collision problem still exists since several meter may wind up transmitting at the same time and have the same transmission period. Thus an interference condition could therefore persist indefinitely.
Some prior systems have proposed detecting when data collisions exist due to several devices transmitting data at the same time. In response to such a data collision detection, the transmission times of one or more of the transmitting devices is then altered. While such systems are feasible, this requires a communication and control path to each of the meter devices which are transmitting so as to alter their transmit times. This involves a substantial additional expense in providing this additional control path. Therefore this is clearly not an optimum solution since it requires providing each meter transmitter with receiver and control circuitry Just to avoid repetitive data collisions.
Some systems have proposed commencing periodic transmission of meter data when the meter reading transmitter first has power applied to it. This provides some transmit time randomization to the transmit data because each meter device will probably be initially activated at a different time. However, when a very large number of meter devices are located in the same general area, there is nothing which guarantees that several meter devices will not have initial power applied to them at times separated by multiples of the transmission period so as to prevent continuous periodic data collisions. An improved data transmission device for use in a system having a plurality of data transmission devices is therefore needed.
The system provides a way to use a single RF channel in a cellular, RF meter reading system. In order to avoid adjacent cell concentrator interference while reducing the overall time required to perform repetitive tasks such as meter reading and performing load survey reads, the system has each of the concentrators send out a general command to all of the meter interface units ("MIUs") in its cell, and the MIUs then each send back their data in turn. In order to accomplish that result, the MIUs in each cell are preprogrammed to transmit a preset time period (different for each MIU in a particular cell) following receipt of the general command requesting data.
A method of and an apparatus (10) for acquiring measurement data from a gage (54, 62) generating a measurement signal representing a dimensional measurement includes a CPU (46) for setting a dwell range representing desired high and low limits for a value of the measurement signal, setting a dwell time representing a desired time period during which the signal value must be within the dwell range, monitoring the signal value generated by the gage at an input port (52, 60) and accumulating an elapsed time beginning when the signal value enters the dwell range, and recording the signal value in a memory (48) when the elapsed time equals the dwell time. The CPU (46) resets the elapsed time when the signal value exits the dwell range and generating an indication by activating an LED indicator (108) when the elapsed time equals the dwell time. The CPU (46) transmits the signal value to a data collection device (70) connected to an output port (68).
A method and apparatus for generating a group of non-repetitive, difficult-to-guess character sets is disclosed. The method includes (a) generating a request for a character set by a client of a character-generating server, (b) sending the request to the character-generating server, (c) generating a pseudo random number required by the character generator; (d) sending the pseudo random number to the character generator; (e) generating a character for the character set by the character generator, (f) sending the character set along with a related key to the client; (g) sending the character set along with the related key to a target server, (h) sending related key to the character-generating server by the target server; (i) re-creating the character set from the related key by the target server; and (j) sending the character set along with the related key to the target server.
A method of reading multiple RFID tags located in a field of an interrogating antenna is based on periodic transmissions from the tags with large, non-transmission intervals between transmissions. The non-transmission intervals are fixed for a given tag, but are random between tags due to manufacturing tolerances in electrical components from which the tag is constructed, such that no coordination of transmissions from the interrogating antenna is required.
In a method for transmitting a desired parameter to a remote location, the desired parameter is first communicated to a base transmitter. Then, the base transmitter transmits a first radio signal therefrom having an unknown center frequency within a known frequency band. The first radio signal comprises information representative of the desired parameter. At a remote location, a remote receiver identifies the center frequency of the first radio signal and tunes the remote receiver to the center frequency thereof so as to facilitate reception of the first radio signal with the remote receiver. The information representative of the desired parameter may then be communicated to a desired destination.
