Field sensor communication system

• US 5,469,156 A
• Filed: 05/01/1992
• Issued: 11/21/1995
• Est. Priority Date: 07/04/1989
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Kogure, Makoto
• Primary Examiner(s): Horabik, Michael
• Application Number:
  US07/877,137
• Time in Patent Office: 1,299 Days
• Field of Search: 340/870.39, 340/870.40, 340/870.38, 340/870.18, 375/5, 455/69, 371/20.1, 371/20.4, 371/20.5, 371/24, 371/71
• US Class Current: 340/870.38
• CPC Class Codes: G08C 19/02 in which the signal transmitted is magnitude of current or voltage G08C19/36, G08C19/38 take precedence

Abstract

A field sensor communication system is arranged in such a manner that, when an electric current, the level of which can be changed to a predetermined level, is, transmitted to a signal transmission line having at least one load resistor connected in series and the voltage change across the load resistor due to the change in the electric current is detected as a reception signal, the predetermined level is cyclically changed to a plurality of levels so that the level at which a good signal reception condition can be realized is determined to perform a communication at the thus determined level. As a result, even if the value of the load resistor in the signal transmission line is changed, the communication can be performed normally, since an undesirable change of the level of the reception signal can be prevented.

Claims

1. A field sensor communication system in which a signal is transmitted/received between at least a field sensor and at least an upper level unit, which is one of an upper level receiving unit and an upper level communication device, via a signal transmission line, at least one of said field sensor and said upper level unit of said field sensor communication system, comprising:

means for determining whether there is any communication error in a received digital transmission signal by comparing the transmitted signal with the received signal; and

means for changing the amplitude level of said digital transmission signal in accordance with an output of said determining means.

2. A field sensor communication system in which an analog signal is transmitted/received between at least a field sensor and at least an upper level unit, which is one of an upper receiving device and an upper communication device, via a signal transmission line, at least one of said field sensor and said upper level unit of said field sensor communication system, comprising:

means for determining whether there is any communication error in a received digital transmission signal, which has been superimposed on said analog signal, by comparing the transmitted signal with the received signal; and

means for changing the amplitude level of said digital transmission signal, which has been superimposed on said analog signal, in accordance with an output of said determining means.

3. A field sensor connected to a signal transmission line, comprising:

means for superimposing a digital transmission signal on a sensor signal to produce a superimposed signal;

means for transmitting said superimposed signal on said signal transmission line;

means for detecting said superimposed signal received from said signal transmission line so as to determine whether there is any communication error in said received signal, by comparing the transmitted signal with the received signal; and

means for changing the amplitude level of said digital transmission signal to be superimposed on said sensor signal in accordance with an output of said detecting means.

4. A unit connected to a signal transmission line, comprising:

means for transmitting a digital transmission signal to said signal transmission line;

means for detecting said digital transmission signal received from said signal transmission line so as to determine whether there is any communication error in said received digital transmission signal by comparing the transmitted signal with the received signal; and

means for changing the amplitude level of said digital transmission signal transmitted by said transmitting means in accordance with an output of said detecting means.

5. A communication device connected to a signal transmission line, comprising:

means for transmitting a digital transmission signal to said signal transmission line;

means for detecting said digital transmission signal received from said signal transmission line so as to determine whether there is any communication error in the received digital transmission signal by comparing the transmitted signal with the received signal; and

means for changing the amplitude level of said digital transmission signal transmitted by said transmitting means in accordance with an output of said detecting means.

6. A field sensor communication system in which a signal is transmitted/received between at least a field sensor and at least one of a receiving unit and a communication device via a signal transmission line, and in which said communication device is connected to said signal transmission line at a position between said field sensor and said receiving unit, said field sensor comprising:

means for superimposing a digital transmission signal on a sensor signal to produce a superimposed signal;

means for transmitting said superimposed signal on said transmission line;

means for detecting said superimposed signal received from said signal transmission line so as to determine whether there is any communication error in said received signal by comparing the transmitted signal with the received signal; and

means for changing the amplitude level of the digital transmission signal transmitted by said transmitting means in accordance with an output of said detecting means;

said at least one of said receiving unit and said communication device comprising;

means for transmitting a digital transmission signal to said signal transmission line;

means for detecting said digital transmission signal received from said signal transmission line so as to determine whether there is any communication error in the received digital transmission signal; and

means for changing the amplitude level of said digital transmission signal transmitted by said transmitting means in accordance with an output of said detecting means.

7. A field sensor communication system in which an analog signal is transmitted/received between a field sensor and a unit, which is one of a receiving device and communication device, via a signal transmission line, at least one of said field sensor or said unit of said field sensor communication system comprising:

means for superimposing a digital transmission signal of predetermined amplitude level on said analog signal to produce a superimposed signal;

means for determining whether there is any communication error in a superimposed signal received from said signal transmission line by comparing the transmitted signal with the received signal; and

means for changing the amplitude level of said superimposed digital transmission signal received from said signal transmission line in accordance with an output of said determining means.

8. A communication device connected to a signal transmission line, comprising:

means for receiving a digital transmission signal via said signal transmission line;

means for determining whether there is any communication error in the received digital transmission signal by comparing the transmitted signal with the received signal; and

means for changing the amplitude level of said received digital transmission signal in accordance with said determining means.

9. A field sensor communication system in which an analog signal is transmitted/received between a field sensor and at least one of a receiving unit and a communication device via a signal transmission line, said field sensor comprising:

means for superimposing a digital transmission signal on said analog signal to produce a superimposed signal;

means for receiving said digital transmission signal, which has been superimposed on said analog signal, from said signal transmission line; and

means for making a comparison between the amplitude level of said received digital transmission signal and a predetermined amplitude level and for changing the amplitude level of said digital transmission signal to a level with which said digital transmission signal can be received without communication error based on the comparison between the amplitude level of said received digital transmission signal and said predetermined amplitude level.

10. A field sensor communication system in which a digital signal is transmitted/received between a field sensor and a unit, which is one of a receiving device and a communication device via a signal transmission line, at least one of said field sensor and said unit of said field sensor communication system comprising:

means for determining whether there is any communication error in a digital signal received via said signal transmission line by comparing the transmitted signal with the received signal; and

means for changing the amplitude level of a digital signal being transmitted in accordance with an output of said determining means.

11. A field sensor communication system in which a signal is transmitted/received between at least a field sensor and at least an upper level unit, which is one of an upper level receiving unit and an upper level communication device, via a signal transmission line, at least one of said field sensor and said upper level unit of said field sensor communication system, comprising:

first means for detecting the coincidence degree between the transmission signal and the received signal and determining the best amplitude level of the transmission signal; and

means for changing the amplitude level of said digital transmission signal in accordance with an output of said first means.