Heartbeat communications

• US 5,631,629 A
• Filed: 02/08/1995
• Issued: 05/20/1997
• Est. Priority Date: 02/08/1995
• Status: Expired due to Term

• Current Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Original Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Inventors: Johnson, Philip E., Delaney, Patrick J. III, Fooks, Elik I.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US08/385,413
• Time in Patent Office: 832 Days
• Field of Search: 340/500, 340/506, 340/507, 340/510, 340/518, 340/539, 340/538, 340/531, 340/825.06, 340/825.16, 340/825.03, 340/870.18, 340/870.16, 340/870.09 , 340/853.2, 340/870.01, 340/870.07, 364/138-141, 364/146, 364/413.02, 364/413.04, 364/413.03, 364/413.06, 359/110, 359/143, 359/164, 359/167, 128/630
• US Class Current: 340/500
• CPC Class Codes: G08B 25/04 using a single signalling line, e.g. in a closed loop
• CPC Class Codes: G08B 29/06 Monitoring of the line circuits, e.g. signalling of line faults

Abstract

A dual channel communications method including: (A) providing a control system with a central control station and a remote sensor for sensing a process status, the central control station and the remote sensor being connected by a power supply line and an output line; (B) impressing a non-periodic high-amplitude process status signal on the output line at the remote sensor so as to transfer status information about the process status to the central control station; (C) simultaneously impressing a periodic low-amplitude low-frequency diagnostic condition signal on the output line at the remote sensor so as to transfer diagnostic information about an operating condition of the remote sensor to the central control station; (D) monitoring the electrical state of the output line at the central control station to detect the level of the non-periodic high-amplitude process status signal so as to receive status information about the process status at the central control station; and (E) monitoring the electrical state of the output line at the central control station to detect the presence of the periodic low-amplitude low-frequency diagnostic condition signal so as to receive diagnostic information about the operating condition of i) the remote sensor, ii) said power supply line and iii) said output line at the central control station.

Claims

1. A dual channel communications method comprising:

(A) providing a control system with a central control station and a remote sensor for sensing a process status, said central control station and said remote sensor being connected by a power supply line and an output line;

(B) impressing a non-periodic high-amplitude process status signal on said output line at said remote sensor so as to transfer status information about said process status to said central control station;

(C) simultaneously impressing a periodic low-amplitude low-frequency diagnostic condition signal on said output line at said remote sensor so as to transfer diagnostic information about an operating condition of said remote sensor to said central control station;

(D) monitoring the electrical state of said output line at said central control station to detect the level of said non-periodic high-amplitude process status signal so as to receive status information about said process status at said central control station; and

(E) monitoring the electrical state of said output line at said central control station to detect the presence of said periodic low-amplitude low-frequency diagnostic condition signal so as to receive diagnostic information about i) said operating condition of said remote sensor, ii) said power supply line and iii) said output line at said central control station.

2. The dual channel communications method of claim 1, wherein said non-periodic high-amplitude process status signal is selected from the group consisting of a square wave signal, a saw tooth wave signal and a sinusoidal wave signal.

3. The dual channel communications method of claim 1, wherein said remote sensor is selected from the group consisting of a photoelectric remote sensor, an inductive proximity remote sensor, a capacitive remote sensor, a magnetic remote sensor and an ultrasonic remote sensor.

4. The dual channel communications method of claim 1, wherein said operating condition of said remote sensor is an operating margin and the step of simultaneously impressing a periodic low-amplitude low-frequency diagnostic condition signal on said output line at said remote sensor is reversibly disabled when said operating margin is inadequate for reliable operation of said remote sensor.

5. A dual channel communications capable control system comprising:

(A) a remote sensor for sensing a process status and an operating condition of said remote sensor, said remote sensor including

i) a switch for switching an output signal from said remote sensor between a first status band and a second status band as a function of said process status in response to information about said process status sensed by said remote sensor so as to transmit status information about said process status and

ii) a modulator for

(a) continuously toggling said output signal within a first diagnostic range, when said output signal is within said first status band, as a function of said operating condition of said remote sensor in response to diagnostic information about said operating condition of said remote sensor so as to transmit diagnostic information about said operating condition of said remote sensor, and

(b) continuously toggling said output signal within a second diagnostic range, when said output signal is within said second status band, as a function of said operating condition of said remote sensor in response to diagnostic information about said operating condition of said remote sensor so as to transmit diagnostic information about said operating condition of said remote sensor;

(B) an output line including a first end and a second end, said first end of said output line being electrically connected to said remote sensor so as to conduct said output signal; and

(C) a central control station for centrally monitoring status information about said process status and diagnostic information about said operating condition of said remote sensor through said output line based on an electrical state of said output signal, said central control station being electrically connected to said second end of said output line, said central control station including

i) a detector for detecting switching of said output signal between said first status band and said second status band so as to respond to changes in said output signal characterized by status information about said process status received from said remote sensor through said output line and

ii) a detector for detecting continuous toggling of said output signal within said first diagnostic range and said second diagnostic range so as to respond to changes in said output signal characterized by diagnostic information about said operating condition of said remote sensor received through said output line,

wherein

1) status information about said process status and diagnostic information about said operating condition of said remote sensor can be simultaneously carried by said output signal over said output line and

2) said operating condition of said remote sensor is an operating margin and said modulator for continuously toggling is reversibly disabled when said operating margin is inadequate for reliable operation of said remote sensor.

6. The dual channel communications capable control system of claim 5, wherein said detector for detecting continuous toggling includes:

(A) a filter for filtering out DC signal components from said output signal so as to produce a filtered output signal;

(B) a transistor that is triggered on when said filtered output signal exceeds a threshold value;

(C) a capacitor that is continuously charged by a power supply and subject to being discharged when said transistor is triggered on; and

(D) a comparator that is responsive to the level of voltage across said capacitor so as to indicate the presence of continuous toggling of said output signal within said first diagnostic range and said second diagnostic range.

7. The dual channel communications capable control system of claim 5, wherein said modulator for continuously toggling includes:

(1) an oscillator;

(2) at least one diode coupled to said output line;

(3) a transistor that is configured to be periodically driven on and off by said oscillator and is connected for shunting said output line around said at least one diode as a means of providing heartbeat modulation when the output is within the first status band; and

(4) a second transistor that is configured to be periodically driven on and off by said oscillator and is connected for shunting said output line with a resistive leakage current path around said at least one diode as a means of heartbeat modulation when the output is within the second status band.

8. A remote sensor for sensing a process status comprising:

(A) a switch for switching an output signal from said remote sensor between a first status band and a second status band as a function of said process status in response to status information about said process status sensed by said remote sensor so as to transmit status information about said process status; and

(B) a modulator for continuously toggling said output signal within a diagnostic range as a function of an operating condition of said remote sensor in response to diagnostic information about said operating condition of said remote sensor so as to transmit diagnostic information about said operating condition of said remote sensor,

wherein

1) said remote sensor can be used with a central control station that responds to changes in said output signal characterized by switching said output signal between said first status band and said second status band by receiving status information about said process status from said remote sensor and does not respond to changes in said output signal characterized by toggling said output signal within said diagnostic range and

2) said operating condition of said remote sensor is an operating margin and said modulator for continuously toggling is reversibly disabled when said operating margin is inadequate for reliable operation.

9. The remote sensor for sensing a process status of claim 8, wherein said modulator for continuously toggling includes:

(1) an oscillator;

(2) at least one diode coupled to said output line; and

(3) a transistor that is configured to be periodically driven on and off by said oscillator and is connected for shunting said output line around said at least one diode as a means of providing heartbeat modulation when the output is within the first status band; and

(4) a second transistor that is configured to be periodically driven on and off by said oscillator and is connected for shunting said output line with a resistive leakage current path around said at least one diode as a means of heartbeat modulation when the output is within the second status band.

10. A central control station for centrally monitoring information about a process status and an operating condition of a remote sensor through an output line based on an electrical state of an output signal, said central control station comprising:

(A) a detector for detecting switching of said output signal between a first status band and a second status band so as to respond to changes in said output signal by receiving status information about said process status from said remote sensor through said output line; and

(B) a detector for detecting continuous toggling of said output signal within a first diagnostic range and a second diagnostic range so as to respond to changes in said output signal characterized by diagnostic information about said operating condition of said remote sensor received from remote sensor through said output line,

wherein

1) status information about said process status and diagnostic information about said operating condition of said remote sensor can be simultaneously carried by said output signal over said output line and

2) said detector for detecting continuous toggling includes;

(a) a filter for filtering out DC signal components from said output signal so as to produce a filtered output signal;

(b) a transistor that is triggered on when said filtered output signal exceeds a threshold value;

(c) a capacitor that is continuously charged by a power supply and subject to being discharged when said transistor is triggered on; and

(d) a comparator that is responsive to the level of voltage across said capacitor so as to indicate the presence of continuous toggling of said output signal within said first diagnostic range and said second diagnostic range.