Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2002-10-17
2004-05-11
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C219S486000, C219S490000, C702S059000, C361S093100
Reexamination Certificate
active
06735496
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to systems and techniques for monitoring heater systems and, more particularly, to systems and techniques for determining current levels and ground fault conditions for multiple control loops of a heater system, such as a heat tracing system.
BACKGROUND
The monitoring of heating and temperature conditions of process system equipment, such as tanks and pipes, is a common industrial practice that may have many applications. For example, heating may be required to maintain heavy oils or resins at a certain viscosity to allow such fluids to be readily pumped through tanks and pipes. Heating also may prevent crystalline precipitation or freezing during a process, or may simply facilitate the process itself. Typically, monitoring and controlling the heating of process system equipment involves the use of heating elements and sensors.
An electrical heat tracing system is one example of a heating system that may be used for protection from freezing, maintenance of an adequate process temperature, and/or de-icing of structures (e.g., tanks, pipes, roofs, gutters).
FIG. 1
illustrates a schematic of a conventional heat tracing system
10
. As shown, the heat tracing system
10
include a controller
12
, a plurality of heater loads
14
a-d
(e.g., heat trace or heat strips), a plurality of control devices
16
a-d
, and a plurality of sensors
18
a-d
,
20
a-d
. A power bus
22
branches into individual connections
24
a-d
for distributing power to each of the heater loads
14
a-d
. Each heater loads
14
a-d
may, in turn, be attached to component needing heat such as a chamber, tank, vessel or pipe.
Each individual branch
24
a-d
of the power bus
22
connecting to the heater loads
14
a-d
includes a control device
16
a-d
and sensors
18
a-d
,
20
a-d
. The control devices
16
a-d
are switches that disconnect the flow of power to the heater loads
14
a-d
from the power bus
22
when actuated by the controller
12
.
The sensors typically include current monitors
18
a-d
and ground fault detectors
20
a-d
. The current monitors
18
a-d
detect changes in the current supplied to the heater loads
14
a-d
and provide control signals to the controller
12
via control lines
28
a-d
. The controller
12
determines when the current supplied to any of the heater loads
14
a-d
falls outside set parameters or meets an alarm condition. The controller
12
actuates the associated control device
16
a-d
and breaks the flow of power to the heater load
14
a-d
with the deviation in the current supply. The controller
12
receives separate signals from each of the current monitors
18
a-d
and individually shuts off power to the heater loads
14
a-d
when an alarm condition is indicated.
The ground fault detectors
20
a-d
detect leakage in current due to a ground fault in the heater loads
14
a-d
. A ground fault in the heating cable involves leakage of current at some location along its length. A ground fault may occur in a system due to mechanical damage, flooding, cable chaffing or corrosion. In the event that one of the heater loads
14
a-d
is grounded, the ground fault detector
20
a-d
associated with the grounded heater load
14
a-d
provides a signal to the controller
12
via one of the control lines
30
a-d
. The controller
12
, in turn, actuates the associated control device
16
a-d
and breaks the flow of power to the grounded heater load
14
a-d
. The controller
12
receives separate signals from each of the ground fault detectors
20
a-d
and individually shuts off power to the heater loads
14
a-d
when a ground fault condition is indicated.
As depicted in
FIG. 1
, each control loop of the conventional heat tracing system
10
is supported by many components including current monitors
1
8
a-d
, ground fault detector
20
a-d
and control devices
16
a-d
. Given that a heat tracing system may have upwards of twenty-four separate control loops, a large number of sensors and detectors employed throughout the heater loads is required. Connecting the controller to the various sensors and detectors requires a great deal of installation and expense. Furthermore, the controller requires numerous inputs and outputs to properly connect to all of the sensors and requires the necessary processing ability to handle signals from the numerous sensors and detectors.
Accordingly, there is a need for monitoring heater systems in a way that overcomes, or at least reduces the effects of, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In one general aspect, a monitoring system includes a sensor that detects operating conditions in a plurality of control loops of a heater system and generates signals corresponding to the detected operating conditions. The monitoring system also includes a controller that receives the signals from the sensor and determines whether the signals indicate the presence of an alarm condition in one or more of the control loops. The controller is configured to temporarily disconnect power to the plurality of control loops when it is determined that an alarm condition is present, determine whether the alarm condition is present in an individual connector loop, and reconnect power to only those control loops in which the alarm condition is not present.
Implementations may include one or more of the following features. For example, the alarm condition may include a deviation in current level and/or a ground fault condition. The sensor may include a current monitor and/or a ground fault detector. The sensor may detect an ampere level of power supplied to the plurality of control loops, and the controller may compare the ampere level against a high setpoint and a low setpoint. The controller may include a database for storing data indicating an alarm condition in one or more control loops.
The monitoring system may include a plurality of control devices. Each control device may be configured to disconnect power to an individual control loop when actuated by the controller. Each control device may include an isolation contactor, a relay, and/or a circuit breaker.
The monitoring system also may include a first sensor and a second senor. The senor may first sensor may detect first operating conditions in the plurality of control loops and the second sensor may detect second operating conditions in the plurality of control loops. The controller may receive the signals from the first sensor and the second sensor and temporarily disconnect power to the plurality of control loops when it is determined that at least one of a first alarm condition and a second alarm condition is present in one or more of the control loops. The first sensor may include a current monitor and the second sensor may include a ground fault detector.
The heater system may include a power bus connecting the sensor and the plurality of control loops. The power bus may have a plurality of braches with each branch distributing power to an individual control loop. The sensor may be located on the power bus before the separation of the power bus into the plurality of branches.
In another general aspect, a monitoring method includes determining whether signals received from a sensor indicate the presence of an alarm condition in one or more control loops. The sensor detects operating conditions in a plurality of control loops of a heater system and generates signals corresponding to the detected operating conditions. The monitoring method also includes temporarily disconnecting power to the plurality of control loops when it is determined that an alarm condition is present, determining whether the alarm condition is present in an individual connector loop, and reconnecting power to only those control loops in which the alarm condition is not present.
Implementations may include one or more of the following features. For example, the alarm condition may include a deviation in current level and/or a ground fault condition. Determining whether the alarm condition is present in an individual connector loop may involve sending a test si
Chromalox, Inc.
Jarrett Ryan
Kirkpatrick & Lockhart LLP
Picard Leo
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