[54] COMMUNICATOR FOR FIELD
INSTRUMENTS AND METHOD FOR
SUPPLYING POWER TO THIS
COMMUNICATOR
[75] Inventor: Makoto Kogure, Katsuta, Japan
[73] Assignee: Hitachi, Ltd., Tokyo, Japan
[ * ] Notice: This patent issued on a continued prosecution application filed under 37 CFR 1.53(d), and is subject to the twenty year patent term provisions of 35 U.S.C. 154(a)(2).
[21] Appl. No.: 08/504,800 [22] Filed: Jul. 20, 1995
Related U.S. Application Data
[63] Continuation of application No. 07/594,983, Oct. 10, 1990, abandoned.
[30] Foreign Application Priority Data
Oct. 13, 1989 [IP] lapan 1-267863
[51] Int. CI. G08B 23/00
[52] U.S. CI 340/870.02; 340/825.05;
340/825.5; 340/870.16
[58] Field of Search 340/870.16, 870.11,
340/870.07, 825.05, 825.06, 825.5, 310.01,
870.02
[56] References Cited
U.S. PATENT DOCUMENTS
4,387,434 6/1983 Moncief, Ir. et al 340/870.16
4,520,488 5/1985 Houvig et al 340/310.01
4,623,871 11/1986 Akano 340/310.01
4,737,787 4/1988 Ito et al 340/870.18
4,797,669 1/1989 McGowan, III et al 340/870.16
4,988,990 1/1991 Warrior 340/870.16
5,122,794 6/1992 Warrior 340/825.05
5,184,121 2/1993 Kogure et al 340/825.5
FOREIGN PATENT DOCUMENTS
0212897A3 8/1986 European Pat. Off. .
02213767A2 8/1986 European Pat. Off. .
0219120A2 10/1986 European Pat. Off. .
0244808 5/1987 European Pat. Off. .
Primary Examiner—Michael Horabik
Assistant Examiner—-Timothy Edwards, Jr.
Attorney, Agent, or Firm—Antonelli, Terry, Stout & Kraus,
LLP
[57] ABSTRACT
A communicator for field instruments connected to a transmission line for transmitting electric signals from the field instruments to a host instrument. The communicator operates on electric power fed from an external power supply over the transmission line. The external power supply is arranged in the transmission line. Electric current consumed by the transmission line is set to a constant value.
11 Claims, 5 Drawing Sheets
