Single frequency multitransmitter telemetry system

• US 4,631,538 A
• Filed: 02/28/1983
• Issued: 12/23/1986
• Est. Priority Date: 02/28/1983
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Carreno, Victor A.
• Primary Examiner(s): Caldwell, Sr., John W.
• Assistant Examiner(s): Heim, Michael F.
• Application Number:
  US06/470,113
• Time in Patent Office: 1,394 Days
• Field of Search: 340/870.18, 340/870.26, 340/825.5, 340/825.73, 371/63, 371/57, 375/88, 375/91, 455/63, 455/206
• US Class Current: 340/870.18
• CPC Class Codes: G08C 15/00 Arrangements characterised by the use of multiplexing for the transmission of a plurality of signals over a common path

Abstract

A telemetry system in which a plurality of transmitters are frequency shift keying modulated. A receiver including an overlapping detector retains the transmitted data when there is no overlap in data transmitted and discards the transmitted data when there is an overlap in data transmitted.

Claims

1. A single frequency multitransmitter telemetry system comprising:

a plurality of sensors with each sensor at a different location;

a plurality of transmitters with each transmitter connected to the output of one of said sensors for transmitting the output of the sensor;

each of said transmitters including means for modulating the output of its sensor in frequency shift keying with frequencies f_o and f_o +Δ

f so that all of said transmitters, when transmitting, transmit one or the other of said frequencies; and

a receiver means including a single receiver input for receiving from all of said transmitters the modulated outputs from said sensors, said receiver means further comprising means for accepting data from said transmitters only one transmitter is transmitting and for discarding data from the transmitters when more than one transmitter is transmitting.

2. A telemetry system according to claim 1 including a plurality of analog-to-digital converter means with each connected to its corresponding sensor for converting the sensor analog output to a serial binary output before it is transmitted.

3. A telemetry system according to claim 2 wherein said modulating means includes means for producing the frequency f_o when the said serial binary output is "1" and for producing the frequency f_o +Δ

f when the said serial binary output is "0".

4. A telemetry system according to claim 3 wherein said receiver means comprises an RF detector having two outputs with the detected f_o appearing on one output and with the detected f_o +Δ

f appearing on the other output and means for retaining the data on said one output when there is no overlapping data on said other output and for discarding the data on said one output when there is overlapping data on said other output.

5. A telemetry system according to claim 4 wherein said means for retaining data when there is no overlapping data and for discarding data when there is overlapping data includes a shift register connected to said one output for collecting words of data transmitted by said transmitters and means connected to said one and said other outputs for gating the data in said shift register out of said receiver each time a word is transmitted, for clearing said shift register after the data has been gated out if there is no overlapping data and for clearing said shift register before the data is gated out if there is overlapping data.

6. A telemetry system according to claim 5 wherein said means for gating the data in said shift register out of said receiver includes a data buffer connected to the output of said shift register, means for enabling said data buffer at the end of each word, for clearing said shift register after said data buffer is enabled if there is no overlapping data and for clearing said shift register before said data buffer is enabled if there is overlapping data.

7. A telemetry system according to claim 6 wherein said means for enabling said data buffer at the end of each word includes logic circuit means response to binary "0"s at both outputs of said RF detector at the end of each word to produce a binary "1" for enabling said data buffer.

8. A telemetry system according to claim 7 wherein said logic circuit means includes an "or" gate having its two inputs connected to the two outputs of said RF detector, an inverter connected to the output of said "or" gate, an "and" gate connected to the output of said inverter and means for applying a binary "1" to said "and" until there is an overlap of data and thereafter applying a binary "0" to said "and" until the end of a word.

9. A telemetry system according to claim 8 including means for connecting the output of said inverter to said shift register to clear said shift register whenever a binary "1" appears at the output of said inverter.

10. A method for transmitting data from a plurality of sensors, said method comprising the steps of:

converting output data from each of the sensors into a serial binary signal;

transmitting the output data from each of said sensors at one or the other of two frequencies using a corresponding plurality of transmitters individual to each of said sensors, the binary "ones" in the serial binary signal from each sensor being transmitted at a first frequency and the binary "zeros" in the serial binary signal from each sensor being transmitted at a second frequency;

receiving the signals being transmitted from said plurality of transmitters at a single input;

frequency detecting the transmitted signal or signals received at said single input to produce output signals corresponding to the first and second frequencies at respective ones of first and second outputs;

retaining the received data when there is no overlapping of binary "ones" corresponding to said first frequency at said first and second outputs; and

discarding the received data whenever there is an overlapping of binary ones corresponding to said first frequency at said first and second outputs.