WO2001082018A2

WO2001082018A2 - Heater control system including satellite control units with integratd power supply and electronic temperature control

Info

Publication number: WO2001082018A2
Application number: PCT/US2001/012840
Authority: WO
Inventors: Dana S. Hauschulz
Original assignee: Mks Instruments, Inc.
Priority date: 2000-04-20
Filing date: 2001-04-20
Publication date: 2001-11-01
Also published as: AU2001259102A1; WO2001082018A3; WO2001082018A8; TW486734B

Abstract

A heater control system that utilizes electronic temperature control at each of a number of interconnected heaters is provided for monitoring and operating heaters within a narrow temperature range. A heater control system is provided that is adapted for controlling a number of heaters positioned on pipe and components of a piping system from a remote location. The heater control system includes satellite controllers mounted on each heater connected daisy-chain fashion and includes a monitoring station with a user interface for allowing a user to monitor and to remotely control the operating status or temperature of each heater in the heater control system. The size of each controller is maintained at a small form factor and a single cord is used to provide power and communications lines to and between the controllers. Each controller integrates power supply and control.

Description

Heater Control System Including Satellite Control Units with Integrated Power Supply and

Electronic Temperature Control

Technical Field:

The present invention relates generally to a system for controlling and monitoring the temperature of heaters and more particularly, to a heater control system that utilizes a number of control units that are configured to provide electronic temperature and power control at each of a number of piping system heaters and to be connected in series and mounted onto the piping system heaters. Background Art:

The use of heaters is widespread in the semiconductor manufacturing, chemical and pharmaceutical processing, plastics manufacturing, food processing, and other industries to heat piping systems to control various production and waste processes. Typically, the temperature of the piping system must be kept within a certain temperature range to achieve a desired production result (e.g., facilitate a desirable chemical reaction) and/or to minimize maintenance on the piping system that can be caused by build up of byproducts in the piping systems or deterioration of the piping systems by corrosion and the like. For example, in the semiconductor manufacturing industry, flexible insulated heaters, such as those disclosed in U.S. Patent No. 5,714,738 to Hauschulz et al., are installed in series along the length of piping and piping components downstream from a reaction or production chamber to maintain transported effluent vapor within a specific temperature range. This temperature control along the length of the piping system acts to minimize the condensation, sublimination, and/or solidification of chemical reaction byproducts on the inner walls of the piping and piping components which, if left unchecked, would eventually require that the piping system components be cleaned or even replaced.

In many industrial applications, the acceptable temperature range for the piping is tight or small, i.e., within a few degrees of a set point, and sometimes, the set point temperature is relatively high, i.e., above 180° C. In the semiconductor manufacturing industry, copper deposition, usually achieved by chemical vapor deposition (CVD), has become one of the most important and rapidly growing areas in integrated circuit manufacturing. Effluent management of copper CVD byproducts requires tight temperature control, such as to within plus or minus 5° C of a set point. In another manufacturing application, titanium nitride CVD involves high temperatures (i.e., about 200° C) and requires that a tight temperature range of about 10° C be maintained in piping and components downstream from a reaction chamber to prevent or minimize condensation of ammonium chloride salt byproducts on the interior walls of the piping and components. Copper CVD and numerous other manufacturing processes illustrate the demand for an accurate and responsive heater control system that allows the user to obtain and maintain temperatures of piping components within user selectable ranges.

The industrial environment in which piping system heaters are used requires that heater control systems satisfy other significant design requirements. Heaters are often placed on piping components that are small, such as 2-inch or smaller diameter piping, where there is little or no clearance between adjacent piping components and structures. Consequently, it is preferable to control or limit the size of the heater control system components. Because of the importance of maintaining the temperature in the piping system, the heater control system preferably is configured to provide the user with operating information during use, such as whether the heater is on or off and whether the heater is within a specified temperature range. Further, the users of the heaters demand that the heaters and any associated control equipment be simple to install, be durable enough for industrial use, and be easy to maintain and/or replace. Of course, the heaters and heater control system must be configured to meet any and all safety standards (e.g., electrical and fire safety standards) that may apply to the particular industry.

One approach that is currently used to provide heater control is to use electro-mechanical temperature controllers installed on each heater. With respect to pipeline heater, these electromechanical temperature controllers are typically either snap-action thermostats or creep-action thermostats, which are generally compact in size and relatively inexpensive. Unfortunately, as will be understood by those skilled in the heating field, temperature controllers that utilize snap-action or creep-action type thermostats generally have a single, fixed temperature set point and provide only limited temperature control.

In this regard, most snap-action electro-mechanical temperature controllers have a 15° C or larger deadband that is unacceptable for the above discussed copper CVD and for other processes requiring tight temperature control because it only provides control of temperature in a 15° C or larger temperature range about a fixed temperature set point. Creep-action thermostats, in contrast, offer a tighter imtial temperature control but then become inaccurate as they drift over time and also have a short service life due to high levels of electric arcing that occurs between its switch contacts. With both types of thermostats, a compact electro-mechanical temperature controller must be configured and installed such that there is intimate thermal contact with the active heater surface of the pipeline heater to properly function. To this end, the general practice is to permanently embed the electro-mechanical temperature controller within the pipeline heater, and when the thermostat fails or needs servicing, the entire heater with controller must be replaced and typically scrapped. Another problem with most electro-mechanical temperature controllers is that they provide little or no operating information during use, and to find a non-functioning heater, operating or maintenance personnel have to touch each of the heaters with their hands to determine if it is warm and therefore, presumably operating. Additionally, the users of these heaters often are left without any accurate information on the actual operating temperature of the heater.

Another approach to heater control is the use of electronic temperature controllers that are positioned remote from the heaters and communicate via numerous electrical power and electronic sensor lines with thermocouples attached to each heater. While standard electronic temperature controllers when combined with thermocouples provide improved control of the heater and a tighter temperature range, they are relatively costly and cumbersome to install. The high cost per controller has led many users to link several heaters together in a zone or piping portion and to place the entire zone under the control of a single controller. Unfortunately, this results in all the heaters being set to a single temperature and, of course, the accuracy of control decreases with the overall size of the zone. A zone typically comprises one master and one or more slave heaters. The temperature sensor used by the single electronic controller is located near or connected to the master heater, and the temperature sensed at this single point in the piping system drives the heater control for all the heaters in the zone. However, the thermal loading and temperature needs may be and often is, different at each of the slave heater locations. The slave heaters may also run hotter or colder than the master heater leading to decreased accuracy or tightness in controlling the temperature throughout the piping system or zone.

The use of single controllers to operate zones also may create safety issues. For example, if the master heater fails cold or low, the controller typically operates or controls the other properly operating heaters to run and overheat the rest of the piping system. In other words, the slave heaters are not properly controlled within the zone and thermally run away resulting in blown fuses and/or fires that cause significant down time or a safety hazard within the manufacturing facility.

Additionally, the controllers are relatively large, e.g., 48 mm by 96 mm by 100 mm, and must be located remote from the heaters due to space and mounting constraints within the typical industrial setting. The size of each controller becomes more of a problem in practice because a protective cage is often placed around the controller to protect sensitive electronic components from inadvertent damage from physical and high temperature sources. Further, installation and maintenance of the remotely-located controllers are problematic because of the number of wires that must be run between each controller and each heater that is controlled by a controller. These wires generally include a power supply line for providing AC power to each heater from the controllers and a temperature sensor line to connect the controller to the thermocouple or other temperature sensing device. For safety and maintenance purposes, these wires are often strapped together which makes it harder for maintenance personnel to work on a single heater or controller. Also, the use of numerous controllers attached from remote locations to numerous heaters (i.e., 6 to 24 heaters on each piping line) creates a "rat's nest" of wiring in the piping system that makes maintenance, upgrading, and troubleshooting of these heater control systems time consuming and difficult for operating and maintenance personnel.

Consequently, there remains a need for an improved heater control system for providing enhanced control and monitoring of heaters used for maintaining the temperature of piping systems within a user selected temperature range. Disclosure of the Invention

It is an object of the present invention to provide a heater control system with enhanced temperature control, i.e., the ability to maintain each heater in a series of heaters within a tight temperature range about a temperature set point.

It is a related object of the present invention to provide a heater control system with user- adjustable temperature set points at or for each heater.

It is another related object of the present invention to provide a heater control system which provides a user with improved heater monitoring and troubleshooting capabilities.

It is another object of the present invention to provide a heater control system that is simple, cost-effective, and safe to install and maintain in typical industrial environments that generally impose significant space restraints on the installation of additional equipment.

Additional objects, advantages, and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by the practice of the invention. The objects and the advantages may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims. To achieve the foregoing and other objects and in accordance with the purposes of the present invention, as embodied and broadly described therein, a heater control system is provided that generally comprises an ac power source that provides ac power on a single power line to a number of satellite heater controllers connected directly to heaters that are installed on piping and piping components. The satellite heater controllers are connected in daisy chain or serial fashion and are configured for easy installation and maintenance by allowing plugging into the heaters (e.g., standard flexible, wraparound pipe heaters) and to the power line. Because the size of each controller is very important due to spacing limitations existing in many industrial environments, the controllers are designed to be contained within a single housing with a small form factor (e.g., about 50 mm by 25 mm by 75 mm) that can be readily mounted on the heaters.

According to one aspect of the invention, the controllers are designed to integrate accurate electronic temperature sensing with power delivery control. In this regard, a preferred embodiment of the invention includes electronic components and circuitry to provide either on/off control or proportional-integrated-derivative (PID) temperature control to effectively control by electronic switching the operation of a heater element of the heater. The components generally include a temperature sensor, such as a thermistor, positioned near the heater surface for sensing temperature and a zero voltage switch with a triac for controlling heater operations quickly without arcing based on the sensed temperature. This electronic temperature sensing and control allows the temperature to be maintained within 4 to 5° C or even more tightly about a temperature set point. In addition to electronic temperature sensing and control, each controller includes its own DC power supply powered by input AC power that functions to energize the electronic components of the controller with DC power. Typical DC voltages range from 3 to 24 volts and are preferably maintained in the range of about 5 to about 12 volts. Electrical isolation is provided between the higher voltage ac lines and lower voltage circuitry. Significantly, this integration and combination of local or internal DC power supply, electronic temperature sensing, electronic control, and electronic AC power switching to the heater within each controller is achieved with only a minimal increase in the overall size of the controller housing.

As can be understood, a key feature of the invention is the inventor's determination of what features are necessary in the satelhte heater controllers to meet industrial users' needs and how these features can be provided with the above discussed and other components in the satellite heater controller and control system while minimizing space requirements. Specifically, it is important to properly determine how much intelligence to build into the satellite temperature controllers and how much intelligence to reserve for or delegate to system management devices, such as supervisory and monitoring computers and devices and the like. In fact, prior to this invention, the general design trend in the controller industry has been to increase the number and range of control features built into electronic temperature controllers, and this trend in design is often referred to as feature creep. In general, additional control features require more supporting electronic circuitry, input devices such as switches and buttons, and output displays. These added support elements increase the size of the controller and take more space when installed while failing to address the significant cabling problem (i.e., the "rat's nest" problem) inherent with prior art remote temperature controllers. In contrast, the inventor has carefully designed the heater control system of the invention so as to restrict or limit the number of options and operational features that are settable at each remote, satellite controller. Note, the heater control system of the invention retains many or all of the sophisticated control options often desired by operating personnel but the adjustment of the settings is preferably accomplished at the supervisory or monitoring computers or devices (i.e., at the systems level). Consequently, from a systems point of view, the heater control system of the invention is able to include the full range of control features without taking up additional space (i.e., without increasing the size of the controller mounted on the pipe heater) by narrowing the scope of the functioning of each satellite controller to the management of its attendant heater and to reliance on the system supervisory or monitoring devices to provide the fuller range of control features. According to another aspect of the invention, the controllers are adapted for temperature adjustment and control at each controller and connected heater. This allows the heater control system to be used to provide user-selectable, and, in many cases, differing temperatures along the length of a piping system which may be useful for numerous process applications and overcomes the problem with prior art devices which used a single, remotely-located controller for numerous heaters connected together in a zone (i.e., that provided the same temperature set point for all heaters connected to the remotely-located controller). In one embodiment, each of the controllers includes a means for setting the temperature locally. In this regard, an 8-position dip switch is included in a preferred embodiment that is accessible by removal or "unplugging" of the controller housing from the heater and AC power and communication lines. The dip switch allows a specific temperature set point to be set, and then the controller operates to provide PID or another regulating type of control to maintain the heater within a temperature range based on the sensed temperature (such as 5° C on either side of the temperature set point). In addition to local control of the temperature set point, another embodiment of the heater control system provides for remote setting of the temperature set point via a user interface at a monitoring station. In this embodiment, the user can quickly change the temperature set point at each controller from a single remote location.

According to a related aspect, the heater control system of the invention provides for effective monitoring of the operating status of each of the controllers and heaters. Preferably, the controllers include visual display on the heater housings for indicating the operating status locally. In one embodiment, three LEDs are used to show an in-temperature-range status, an under- temperature-range status, and an over-temperature-range status. In another embodiment, monitoring of the controllers and heaters is accomplished remotely by including a base station with a LED display that indicates when any heater in the line is under temperature range, when all the heaters are within set temperature ranges, and when any heater in the line is over temperature range. More sophisticated remote monitoring is provided in another embodiment that includes a monitoring station that has a user interface with a monitor that can be used to display all or portions of the heaters controlled by the heater control system. In addition to visual display of status indicators, audio alarms are included in some systems to quickly alert operating personnel to out-of- temperature-range occurrences.

Other features and advantages of the invention will become clear from the following detailed description and drawings of particular embodiments of the heater control systems and associated combinations and methods of operating the heater control systems steps of the present invention. Brief Description of the Drawings

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the preferred embodiments of the present invention, and together with the descriptions serve to explain the principles of the invention. In the Drawings:

Figure 1 is a functional block diagram of a heater control system of the present invention as it may be utilized with a series of pipe heaters.

Figure 2 is a functional electrical block diagram of a controller of the heater control system of Figure 1 and the connected heater.

Figure 3 is an electrical schematic of the controller and connected heater of Figure 2.

Figure 4 is a functional block diagram of an alternate heater control system of the present invention including a monitoring station in communication with three pipeline heater systems having base stations and satellite heater controllers.

Figure 5 is a functional electrical block diagram of one of the base stations and controllers and interconnected heaters of Figure 4.

Figure 6 is a perspective view of one of the controllers of Figure 4 connected to, or plugged into, a pipe heater to illustrate the compact size and shape of the controllers. Figure 7 is a side view of the controller and heater of Figure 6.

Figure 8 is an end view of the controller and heater of Figures 6 and 7.

Figure 9 is a perspective view of the controller of Figures 7 and 8 unplugged from the heater board and connector showing the 8 position dip switch used in one controller embodiment to facilitate setting a temperature set point at each controller. Best Mode for Carrying Out the Invention;

With the above brief summary of the invention understood, it may be helpful in understanding the invention to discuss in detail two specific embodiments of heater control systems that each incorporate a number of the unique features of the invention. Each of the embodiments incorporates electronic temperature control at each heater to provide accurate control of the temperature of each heater (e.g., within about 2°C of a temperature set point) while also overcoming power and communication cable problems. The following discussion will begin with a detailed description of the features of a heater control system that is useful for controlling a number of heaters installed in series (such as on a pipe line). This first embodiment of a heater control system includes features that, among other things, allow a temperature set point to be selected at each heater and allow a single alternating current (AC) power source to be utilized to power or drive both the attached AC heaters and the DC electronics in each controller. A second preferred embodiment of a heater control system will then be discussed which includes some of the features of the first heater control system (such as a unique temperature set point at each heater) but adds numerous other features that facilitate its use in more complicated heater arrangements. In this regard, this second embodiment includes features that allow remote monitoring of numerous heater systems and of the individual heaters in each heater system. As will become clear from the following description, both of the heater control systems are well-suited for use in controlling the heating of piping systems. Clearly, though, the invention is broad enough in concept to be useful in numerous other heater control applications where it is desirable to control the operation of a number of heaters, and these other applications, although not described in detail, are intended to be included within the scope of this invention.

Referring to Figures 1, 2, and 3, a heater control system 10 according to the invention is illustrated that is useful for controlling the operation of a number of heaters that, due to the features of the invention, can be daisy-chained together as shown in Figure 1 to effectively heat the pipe 12 to desired temperatures along the length of the pipe 12. Generally, the heater control system 10 includes an AC power source or supply 14 that provides AC current (typically, 12 amps or less for safety reasons) for the heater control system 10. Because it is preferable for improved safety and ease of installation and maintenance that the number of wires or lines used for supplying power to controllers and heaters in the heater control system 10 be minimized or even, as illustrated, kept to a single power line, the heater control system 10 provides power control in each controller.

In this regard, the AC power supply 14 provides AC current over lead 16 to the first controller 18 in the series of similar controllers 22, 26, 30, 34, and 38 that are daisy-chained together to control heating the pipe 12. Figures 2 and 3 illustrate an electrical block diagram and an electrical schematic, respectively, of the controller 18 and its connection with heater 19 (of course, Figures 2 and 3 are also representative of the other controllers 22, 26, 30, 34, and 38 and the corresponding heaters 23, 27, 31, 35, and 39, respectively). The schematic of Figure 3 is exemplary of the type of circuitry that can be employed to obtain the functions of the invention but other circuitry and components can readily be substituted and are within the breadth of the invention. The heater 19 may be any typical pipe heater design, such as those described in U.S. Patent No. 5,714,738 to Hauschulz et al., and as shown contains a heater element 40 that typically operates on AC current. To allow the controllers 18, 22, 26, 30, 34, and 38 to be daisy-chained together with electronics operating on DC power and yet to provide AC current to the heaters 19, 23, 27, 31, 35, and 39, the electrical configuration of Figures 2 and 3 is utilized. The AC power entering the controller 18 from lead 16 is allowed to pass through the controller 18 to the outlet lead 20 to the next controller 22. Note, that although the heaters 19, 23, 27, 31, 35, and 39 appear to be wired in series for convenience of illustration, they typically are wired in parallel with each heater 19, 23, 27, 31, 35, and 39 supplied with the full voltage available at the AC power supply 14. The controller includes a DC power supply 42 that takes AC current received on leads 43 and 44 to power the control electronics via the lead indicated by VCC. In this manner, a single AC power source 14 with a single string of power leads 16, 20, 24, 28, 32, 36 that can be plugged or otherwise connected can be utilized to operate a number of heaters 19, 23, 27, 31, 35, and 39.

According to another significant feature of the invention, electronic temperature control is incorporated into each controller 18, 22, 26, 30, 34, and 38 rather than being provided at one multichannel remote controller. As discussed above, electronic temperature control is important for achieving tight temperature ranges about a user-specified temperature set point, and in a preferred embodiment, the temperature of each heater 19, 23, 27, 31, 35, and 39 is controlled within about 5° C and more preferably within about 2° C of a temperature set point. Clearly, the configuration of the electronic temperature control utilized to achieve these functions can be selected to provide a number of controls, such as on-off regulation, proportional ("P") regulation, proportional-derivative ("PD") regulation, proportional-integrated-derivative ("PID") regulation, or auto-tuning regulation, depending on the needs of the heater control system 10 user.

As illustrated in Figures 2 and 3, on/off electronic temperature control is incorporated in the controller 18 and in a preferred embodiment allows temperature set points to be set by changing the value of the reference voltage, V_RH?, applied to the sense amplifier 48. One method that can be used with the invention to change the V^ is to use a resistive voltage divider that includes an adjustable potentiometer, and this and other methods of setting the V_REF are readily understood by those skilled in the art of electronic temperature controller design and are considered part of the invention. On/off control functionality is achieved by the inclusion of a temperature sensor 46 positioned adjacent the heater surface 41 which provides an output signal on lead 47. The temperature sensor 46 may be any of a number of sensors such as a J, K, S, R, T-type thermocouple, thermoresistance circuitry, or a thermistor with a temperature range selected to suit the application, such as 20 to 230° C for the semiconductor manufacturing industry. In a preferred embodiment, the temperature sensor 46 is a thermistor that is part of a resistance bridge circuit that provides an output voltage signal over lead 47 to a sense amplifier 48 that compares the received signal to the reference voltage, V_REF, and transmits an actuating signal to the AC power switching device 52.

The sense amplifier 48 allows a temperature set point, preferably with a resolution of 1° C, to be input and adjusted by the user. The switching device 52 includes a zero voltage switch and triac to accurately and quickly switch the heater element 40 on and off based on the output signal of the temperature sensor 46. Together the components of the switching device 52 function to provide high electrical isolation between the high voltage AC lines 16, 20 and the more delicate low voltage (e.g., about 5 V) electronic circuits to improve electrical safety. The switching device 52 is also very fast relative to electro-mechanical switches that are used in prior devices and minimizes problems with arcing and contact erosion that occur with electro-mechanical switches. Additionally, a unique temperature set point can be set at each controller 18, 22, 26, 30, 34, and 38 by independently adjusting the reference voltages, V_REF, supplied to the inputs of their respective sense amplifiers 48, thereby allowing the heater control system 10 to better control the pipe 12 temperature. For example, it may be desirable to gradually increase or decrease the temperature of the pipe 12 along its length, which is easily achievable with the present invention.

According to another feature of the invention, the operation of each heater 19, 23, 27, 31, 35, and 39 is visually indicated at each controller 18, 22, 26, 30, 34, and 38 to allow operation and maintenance personnel to monitor the heater control system 10 and to replace or service malfunctioning controllers. In this regard, with the features of the invention, this replacement of a single controller can be achieved readily be simply unplugging the malfunctioning controller and plugging in a replacement, as will be discussed more fully in conjunction with Figures 6-9. Referring to Figures 2 and 3, the functioning of the heater 19 and the present temperature of the heater surface 41 are monitored with a window comparator 50 which monitors the output of sense amplifier 48 via lead 49. A system of three LEDs is used to externally display the functioning of the heater 19. Although numerous colors and fewer or greater numbers of signals may be utilized, in the illustrated embodiment, a blue LED is used to display (when illuminated) that the heater surface 41 is under the temperature set point (or temperature range), a green LED is used to display that the heater surface 41 is within the temperature range, and a red LED is used to display that the heater surface 41 is over the temperature range. In this manner, the operation of heater control system 10 can be quickly monitored by personnel with a visual check.

In an alternate embodiment (not shown), radio frequency (RF) communications are sent via the AC power lines 16, 20, 24, 28, 32, and 36 to allow the operation of the heaters 19, 23, 27, 31, 35, and 39 to be remotely monitored. In this embodiment, RF signals are generated with a RF tone generator or the like and are sent along the AC power lines 16, 20, 24, 28, 32, and 36 using the X- 10 standard or alternate communications standard, and are monitored with a RF signal decoder (not shown) or a similar device at a remote location to identify which heaters 19, 23, 27, 31, 35, and 39 are operating within or outside the desired temperature ranges.

While the heater control system 10 provides a number of advantages over prior art devices, it provides limited remote monitoring capabilities and does not necessarily address all of the problems associated with integration of heater control systems into more complicated industrial settings. To address these additional needs, a heater control system 70 is shown in Figure 4 that allows a user to remotely monitor and, in some cases, to remotely operate a number of heater systems. As shown in Figure 4, the heater control system 70 generally includes a monitoring station 72 with a user interface 74 (i.e., a monitor, with or without a touch screen capability, a keyboard(s), a mouse, and other peripheral computer interface equipment), a central processing unit (CPU) 76 in communication with the user interface 74 and memory 78 which may contain software for use in monitoring and controlling heaters and heater controllers, databases with temperature "recipes" for various processes and other temperature and maintenance information, and a communication port 80 for receiving and transmitting digital data. The monitoring station 72 is connected with communication lines 81, 82, and 83 to pipe heater control systems 84, 86, and 88, on pipes 85, 87, and 89, respectively. During operation, the monitoring station 72 allows a user at a remote location to quickly monitor the temperature of each heater in the heater control systems 84, 86, and 88 and in some embodiments, to transmit commands via the communication lines 81, 82, and 83 to change the temperature settings of the individual heaters or otherwise control operation (e.g., turn the heaters on and off). In this fashion, a single monitoring station 72 can be used to control and monitor a very large number of heaters and heater systems (although only three are shown for ease of illustration). To more fully understand the operation and use of the monitoring station 72, its integration with a single pipe heater control system 86 will be discussed in detail in connection with the description of the components of the control system 86. Of course, it will be understood from the following discussion that the control system 86 may be utilized separate from the heater control system 70 because it provides useful advantages over the heater control system 10.

As with the heater control system 10, it is preferred that the pipe heater control system 86 provide control and supply power to a number of controllers and heaters with the use of a minimum number of leads, wires, and/or lines to avoid the rat's nest problem that is prevalent with prior art control systems. In this regard with reference to Figures 4 and 5, the pipe heater control system 86 includes a base station 92 that communicates with the monitoring station 72 via communication line 82 and receives AC power from a single AC power supply 90 over line 91. The base station 92 includes a digital input and output device 116 for communication with the monitoring station 72 and a digital I O 112 for transmitting commands and information requests from the monitoring station 72 and the base station 92 to satellite controllers 96, 100, 104 and for receiving digital signals from the same controllers 96, 100, 104. In a preferred embodiment, both of these communication interfaces are configured to use both the EIA RS-232 and RS-485 standards at a fixed baud rate of 9600 baud. The base station 92 includes an optional ground fault interrupt 106 and a 12-amp circuit breaker 108 for increasing the operating safety of the control system 86 and for isolating the satellite controllers 96, 100, 104 from the AC power supply 90 in the event of a short circuit or ground fault condition. Additionally, the base station 92 includes a DC power supply 110 (e.g., a 9- volt DC power supply) for supplying DC power for electronic temperature control components of each satellite controller 96, 100, and 104.

In the preferred embodiment illustrated, the AC power output, DC power output, and digital I/O lines are integrated and/or contained within a single communication/power line 94 that is passed to the first satellite controller 96. Further, the line 94 is illustrated as coiled in Figure 4 because this further enhances ease of installation and maintenance as the specific location of each controller 96, 100, and 104 and the distance between the same may vary with each application. With the combination of a coiled line 94 (as well as lines 98 and 102) and integration of power and communication lines into a single line 94 (and lines 98 and 102), the control system 86 is able to readily achieve the goals of minimizing the complexity of the system, reducing space requirements, and increasing the ease of installation and replacement (i.e., each line 94, 98, 102 and controller 96, 100, and 104 can be individually plugged into the system 86).

To allow a single line to be fed from the base station 92, it is important that power and communication lines be passed through each satellite controller 96, 100, and 104 to allow the satellite controllers 96, 100, and 104 to be daisy-chained together. This integration of power and temperature sensing and control at each satellite controller 96, 100, and 104 is achieved as illustrated in the functional block diagram of Figure 5.

Significantly, this integration of control functions allows each of the satellite controllers 96, 100, and 104 to be housed in a single housing 148 illustrated in Figures 6-9. Additionally, the size of the housing 148 is maintained relatively small (i.e., a width, W, of less than about 64 mm, a height, H, of less that about 32 mm, and a length, L, of less than about 70 mm). The satellite controller 96 and housing 148 are configured, in this exemplary embodiment, for mating with a docking port attached to a wrap around flexible pipe heater 97. The docking port includes a flexible mounting pad 152 shown with a heater board. The flexible mounting pad/heater board 152 includes power/communication receptacles 150 at each end, temperature sensing connections, and power connectors to the detachable satellite controller 96. Significantly, integrating the satelUte controller 96 with the heater 97 via the docking port arrangement beneficially eliminates about 2 to 4 meters of power and sensor cable, and this elimination of cable occurs for every satellite controller 96 deployed in the heater control system 70. The receptacles 150 allow quick connection with power/communication lines 94 and 98. The controller 96 with its associated housing 148 and mounting portion/heater board 152 is configured for ease of installation and servicing, and, significantly, to provide a very small form factor relative to existing temperature controllers (that often only provide temperature control without integrating power switching functions).

Referring again to Figure 5, the controller 96 is configured to receive AC power from the base station 92 via line 94 on leads 124 which are directed into the heater 97. The heater 97 includes heater element 126 that operates on the AC power on leads 124 and is electronically controlled (i.e., turned on and off) via leads 128 and 131 by opto-coupler zero voltage switch 130 (although other electronic switching devices may readily be utilized). The controller 96 brings DC power in with leads 120 which power the microprocessor 134 and other electronic components via leads 132. The microprocessor 134 is included to provide better control over the temperature settings of the heater 97, to operate operational displays at the controller 96, to operate the switch 130 to maintain temperatures within a desired and user adjustable range, and to provide digital communication capability with the base station 92 and in some cases, the monitoring station 72.

During operation, the temperature sensor 142 (e.g., a thermistor, thermocouple, or the like) which is positioned adjacent the heater surface 127 responds to temperature changes in the heater surface 127 and outputs on lead 143 a representative signal (such as a voltage signal). Sense amplifier 144 amplifies this signal and transmits an analog signal to the microprocessor 134 which includes an analog to digital converter 136. The microprocessor 134 is configured to process the digital signal to determine the temperature of the heater surface 127. The microprocessor 134 then determines if the heater surface 127 temperature is within an acceptable range about a temperature set point.

According to the invention, the controller 96 is preferably adapted to allow a user to control (i.e., set and later adjust) the temperature at which the heater 97 is operated. Typically, this is achieved by setting a temperature set point and, in some embodiments, a range of variation about this set point (or the temperature band about the temperature set point may be fixed by the electronic temperature control technique utilized, e.g., if on-off control is used with turning on a heater at a low temperature setting and turning the heater off at a high temperature setting). As illustrated in Figures 5 and 9, the controller 96 includes an 8-position dip switch 140 which allows the user to either manually set the temperature set point (e.g., by setting the binary number of a desired temperature in the 8 position dip switch) or remotely by setting all the switches of the dip switch 140 to zero or other designated remote mode settings and then remotely communicating a temperature set point to the microprocessor 134 via digital communication lines 122 from the monitoring station 72 (which is stored in memory of the microprocessor 134). As illustrated, the dip switch 140 is accessed by unplugging the controller housing 148 from the docking port of the mounting portion 152 of the heater 97. During operations, the microprocessor 134 compares the temperature determined from signals from the temperature sensor 142 with the temperature setting of the 8 position dip switch 140 via lines 141 or the temperature received from the monitoring station 72 to verify whether the heater surface 127 is within an acceptable temperature range (such as, for example, within 5° C and more preferably within about 2° C of the temperature set point). If the heater surface 127 temperature is under the acceptable temperature range, the microprocessor 134 functions to operate the switch 130 to operate the heater 97 and to communicate this low temperature to the base station 92 over leads 138 and 122.

Referring to Figure 5, the base station 92 may have its own operation status display 114 and/or an alarm status relay 118 for activating audio and visual alarms either at the base station 92 or at a remote location (e.g., a flashing light that is readily visible from a distance). In a preferred embodiment, the operation status display 114 "lights" a blue LED when one of the heaters 97, 101, or 105 is under its set temperature range, lights a green LED when all of the heaters 97, 101, and 105 are within their set temperature ranges, and lights a red LED when one of the heaters 97, 101, or 105 is above its set temperature range. The base station 92 concurrently transmits the temperature and operating information for each heater 97, 101, and 105 to the monitoring station 72 where it can be displayed on the user interface 74 and/or stored in memory 78.

Referring again to Figure 5, the microprocessor 134 also functions to operate a local display 146 with three colored LEDs similar to that discussed for the base station 92 that enables a user to quickly, visually monitor each of the heaters in a pipe line. The LED display 146 is readily visible on the upper, exterior portion of the controller housing 148 (see Figure 6). The microprocessor 134 continues to monitor and compare the heater surface 127 temperature and once the temperature reaches a predetermined point within the temperature range the microprocessor 134 functions to operate the switch 130 to turn off the heater 97, communicate "within range" information to the base station 92 (and thereby, the monitoring station), and operate the display 146 of the controller 96. The microprocessor 134 then continues to momtor the temperature of the heater surface 127 to communicate if the temperature is over or out of an acceptable range and to repeat the above operations when the temperature falls under the preset temperature range. The control logic exercised by the microprocessor 134 can be a simple on/off control, a version of PID control, and other control functions.

In the above manner, the temperature of each heater 97, 101, and 105 can be set and maintained within a relatively tight temperature range (such as a 1 to 2° C range). Significantly, the use of a monitoring station 72 and remotely programmable controllers 96, 100, 104 allows a user to establish and rapidly change the temperatures of each of the heaters 97, 101, and 105 to establish relatively complex recipes for changing processes. Further, the configuration of the heater control system 70 allows a user to remotely and locally monitor the operation of each controller 96, 100, 104 and heater 97, 101, 105 to enhance process monitoring and to decrease the time spent on troubleshooting. To further maintenance, each of the controllers 96, 100, 104 is designed to allow a user to unplug a single controller 96, 100, or 104 and/or its associated power/communication lines 94, 98, 102 and plug in replacements.

During operation, the base station 92 operates to at least periodically, such as once every 2 seconds or some other fixed time period, poll the connected controllers 96, 100, 104 for status (e.g., temperature) and diagnostic information. To monitor the life of certain components of the controller 96, a counter mechanism or routine may be included within the microprocessor 134 to track the times they are operated. For example, electro-mechanical relays typically have a fixed operating life and it may be useful to include a counter for each included electro-mechanical relay to count the times they are activated. Once the preset number is reached, the microprocessor 134 sends this information to the base station 92 to establish a maintenance flag for the controller 96.

Since numerous modifications and combinations of the above method and embodiments will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and processes shown and described above. For example, in Figure 4, a separate AC power supply and base station was shown for each pipe line and this configuration was selected to easily comply with certain electrical safety standards. Of course, the illustrated heater control system 70 can be modified to include a single AC power source and a single base station that together provide AC power to multiple control systems 84, 86, and 88. Accordingly, resort may be made to all suitable modifications and equivalents that fall within the scope of the invention as defined by the claims which follow. The words "comprise," "comprises," "comprising," "include(s)," and "including" when used in this specification and in the following claims are intended to specify the presence of stated features or steps, but they do not preclude the presence or addition of one or more other features, steps, or groups thereof.

Claims

Claims:

1. A heater controller for monitoring and controlling the operation of a heater, comprising: an AC power inlet for connecting the heater controller to an AC power source to receive AC power; an electronic temperature controller having a temperature sensor adjacent a heater surface of the heater for sensing the temperature of the heater surface and in response transmitting a signal and an electronic switch connected to the heater element and the temperature sensor, wherein the electronic switch operates to receive and process the signal from the temperature sensor and to selectively apply the received AC power to the heater element in response to the signal to control the temperature of the heater surface within a temperature range about a temperature set point; and a power supply connected to the AC power inlet and the electronic temperature controller adapted for supplying the received AC power to the electronic temperature controller in an acceptable power form for use in operating the temperature sensor and the electronic switch of the electronic temperature controller.

2. The heater controller of claim 1, further including an AC power outlet connected to the electronic switch and the AC power inlet adapted for outputting AC power to a second heater controller connected to the AC power outlet.

3. The heater controller of claim 1 , wherein the acceptable power form for the electronic temperature controller is DC power and the power supply includes an AC to DC converting device.

4. The heater controller of claim 1, wherein the electronic switch includes a temperature input for setting the temperature set point.

5. The heater controller of claim 4, wherein the temperature input is an 8-position dip switch.

6. The heater controller of claim 1, wherein the temperature range is less than about 5° C on either side of the temperature set point.

7. The heater controller of claim 1, further including a housing configured to contain the AC power inlet, the power supply, and the electronic temperature controller and further including an operational status display connected to the temperature sensor adapted for providing a heater surface temperature indication based on the signal from the temperature sensor on an external surface of the housing.

8. The heater controller of claim 7, wherein the operational status display includes a first LED corresponding to a heater surface temperature under the temperature range, a second LED corresponding to a heater surface temperature within the temperature range, and a third LED corresponding to a heater surface temperature over the temperature range.

9. The heater controller of claim 7, further including wherein the housing has a width of less than about 64 millimeters, a height of less that about 32 millimeters, and a length of less than about 70 millimeters.

10. The heater controller of claim 1, further including a transmitter connected to the temperature sensor for transmitting temperature information based on the signal to a remote monitoring location.

11. The heater controller of claim 1 , wherein the switch comprises a zero voltage switch.

12. A heater control system for monitoring and controlling operation of a plurality of heaters, comprising: a heater controller attached to each of the heaters, wherein each heater controller includes an electronic temperature sensing and control system for sensing the temperature of a heater surface of the attached heater and for controlling operation of the heater based on the sensed temperature and further includes a DC power inlet and outlet, a communication inlet and outlet, and an AC power inlet and outlet; and a base station connected to a first of the heater controllers, the base station being configured for communicating with each of the heater controllers and providing AC and DC power to each of the heater controllers through the first heater controller.

13. The heater control system of claim 12, wherein the heater controllers are communicatively and electrically connected to adjacent heater controllers through the DC power inlets and outlets, the communication inlets and outlets, and the AC power inlets and outlets of the heater controllers.

14. The heater control system of claim 13, wherein the electronic temperature sensing and control system is connected to the DC power inlet and the commumcation inlet and the heater is connected to the AC power inlet.

15. The heater control system of claim 13, wherein the communication connection and the electrical connection between adjacent heater controllers comprises a single cable having a coiled configuration, whereby distances measured between the adjacent heater controllers can vary within a predetermined range.

16. The heater control system of claim 12, wherein the electronic temperature sensing and control system includes a temperature sensor for sensing the temperature of the heater surface and in response transmitting a signal, an electric switch in contact with a heater element of the heater and the AC power outlet, and a processor for processing the signal and operating the electronic switch based on the processed signal to operate the heater element.

17. The heater control system of claim 16, wherein the electronic temperature sensing and control system further includes a temperature input communicatively linked to the processor for setting a temperature set point, the processor being configured to compare the processed signal with the temperature set point to operate the electronic switch to maintain the heater surface in a temperature range about the temperature set point.

18. The heater control system of claim 17, wherein the temperature input is an 8- position dip switch.

19. The heater control system of claim 17, wherein the temperature range is less than about 5° C.

20. The heater control system of claim 17, wherein the electronic temperature sensing and control system includes an operation status display connected to the processor for visually displaying at the heater controller a first state corresponding to a sensed temperature under the temperature range, a second state corresponding to a sensed temperature within the temperature range, and a third state corresponding to a sensed temperature above the temperature range.

21. The heater control system of claim 17, wherein the base station includes an input and output device for communicating operating information to and from the heater controllers, the operating information including sensed temperatures and temperature set point commands whereby the base station is operable to remotely set the temperature set point of each of the heaters.

22. The heater control system of claim 21, further including a second base station connected to a heater controller, not linked to the first heater controller, and a monitoring station communicatively linked to the base stations, the monitoring station being configured for receiving and transmitting the operating information to and from each of the base stations.

23. The heater control system of claim 12, wherein the base station includes an AC power inlet for receiving AC power from an AC power source and includes a DC power supply for converting the received AC power to DC power and for transmitting the DC power to the heater controllers.

24. A method of controlling operation of a series of heaters, comprising: coupling a heater controller to each of the heaters, each heater controller being positioned with a temperature sensor of the heater controller adjacent a heater surface of the coupled heater and including an AC power inlet and outlet and an electronic switch electrically connected to the temperature sensor and electrically contacting the heater surface during the coupling; connecting an AC power source to the AC power inlet of a first of the heater controllers; providing AC power to each of the other heater controllers via the AC power outlet of the first heater controller by electrically connecting adjacent ones of the heater controllers at the AC power inlets and outlets, respectively, of the adjacent heater controllers; setting a temperature set point for each of the heater controllers; sensing a temperature of each of the heater surfaces of the heaters with the temperature sensors; and operating the electronic switch of each of the heater controllers in response to the sensed heater surface temperature to maintain each of the sensed heater surface temperatures within a temperature range about the temperature set point of the corresponding heater controller.

25. The method of claim 24, wherein the temperature setting is completed manually at each heater controller by operating a temperature input.

26. The method of claim 24, wherein the temperature setting is completed remotely by transmitting operating information to each heater controller from a base station, the heater controllers being communicatively linked with the base station.

27. The method of claim 24, further including converting within each heater controller the received AC power to DC power and supplying the DC power to the temperature sensor and the electronic switch.

28. The method of claim 24, further including displaying at each heater controller an operational state of the heater coupled to the heater controller.

29. The method of claim 28, wherein the operational states are selected from the group consisting of under the temperature range, within the temperature range, and over the temperature range.

30. The method of claim 29, wherein the temperature range is less than about 5° C.