1473259333-GasAirControlSystemforGasBurners.pdf (Size: 4.06 MB / Downloads: 3)
Wayne Combustion Systems (WCS) builds burners for oven and furnace applications that
require a control circuit to regulate the combustion fan and gas valve of the burner to maintain a
desired temperature. The current control board is built and owned by another company, which
increases the cost of the end appliance and limits the ability to make any changes. In order to
lower the cost of building the board and making changes, WCS needs a new control circuit
designed along with the accompanying software so that WCS can make changes easily and keep
the cost of making the board low.
The board will need to control a safety ignition, combustion fan, and gas valve in response to a
thermostat input and circulator fan speed input. The fan speed and valve position are controlled
based on parameters that WCS sets with the developed desktop application. Additionally, the
board will need the ability to select different parameters and operation modes using mechanical
switches on the board. This will be achieved by determining the requirements and parameters,
breaking down the system into sub-systems, coming up with several different conceptual
solutions for each sub-system, and after evaluating the solutions combine them into a complete
conceptual solution. Therefore, this project will allow WCS to easily make modifications to the
system while achieving the desired goal of $30 or less per board.
The requirements were defined as a system with user-friendly computer based application, quick
troubleshooting interface, and an interface that works with a wide range of burner applications.
The parameters were determined by the systems inputs and outputs and their characteristics. The
systems were then divided into seven sub-systems, including the microcontroller, computer I/O
interface, voltage regulator, troubleshooting interface, and others. For each sub-system, several
possible conceptual solutions were generated and evaluated to determine the best solution when
weighted against the requirements and design variables. The chosen conceptual solution uses
LabVIEW for the computer software, an 8-pin DIP switch for hardware mode selector, surfacemount
flashing LEDs for the troubleshooting interface, and a LPC1343 microcontroller. The cost
of all the components for the chosen conceptual solutions is $24.70, therefore this final solution
will meet the design requirements, allow WCS to easily make modifications to the system, and
meet the cost constraint.
Section 1.1: Requirements and Specifications
i. Fan motor, gas valve opening, and ignition safety relay control in response to
thermostat signal and fan feedback
The board must output control signals to the gas valve control and fan motor, as
well as enabling the ignition safety relay to begin burner operation. The actual gas
valve output should be +/- 10mV of the desired signal.
ii. User friendly computer based application to test and program system
As a companion to the onboard software, a desktop computer program must be
able to interface with the board by loading map tables, setting specific software
control parameters (e.g. control loop parameters), and reading/analyzing available
feedback from the board. The desktop program must also be able to export the test
data to an external file.
iii. Quick troubleshooting interface
The burner control board must use an indicator to alert the user to the current
state of the board and also to relay troubleshooting information.
iv. Hardware operation selector
The burner control board must have a method of changing the basic burner
control algorithm for the specified application via an on-board hardware selector.
v. Interface with a wide range of burner applications
The board should be able to adapt to a variety of blower fan situations that Wayne
Combustion manufactures, specifically the entire family of products of the
Pelonis Technologies P1232-28 24VDC Fan Blowers.
vi. Control system for fan controller
By combining the thermostat control input with the control loop of the fan PWM
feedback signal, the board will be able to intelligently adjust for any wear or
imperfections in the blower fan, such as motor wear. This should allow the motor
to maintain the desired output +/- 25 RPM.
vii. Final Board Production Cost
Since one of the purposes of this project is to reduce the cost of production. The
final board needs to be $30 or less per unit when purchasing 2000 units per
Section 1.2: Given Parameters
The given, or fixed, parameters are those that will be the guidelines for the design of the
Gas/Air Control for the oven. The following is the list of the given parameters.
i. The gas/air control will be powered by a 24VDC input
The board is supplied power from a regulating power supply, which provides a
24VDC signal up to ~1.0A.
ii. The gas/air control must be able to interface with existing systems
The following are the various components that the control must be interfaced
a. Combustion Blower
The gas/air control must be able to interface with the specific combustion
blower that is a PWM signal that varies from 0-24VDC.
b. Gas Valve Control
The gas/air control must be able to interface with the gas valve control that is
a PWM signal that varies form 0-15VDC.
c. Ignition Safety Relay
The gas/air control must interface with the Ignition safety relay.
d. Blower Fan Tachometer
The gas/air control must interface with a Hall Sensor that acts as a
tachometer and outputs a PWM signal.
The gas/air control must interface with the thermostat with either DC 0-10V
Section 1.3: Design Variables
When designing a solution to the given problem, there are several elements that can be
varied in order to satisfy the requirements and specifications, and work with the
limitations and constraints. These design variables allow the designed solution to achieve
the necessary characteristics specific to the problem. They include hardware that can be
selected based on the needed properties, as well as software components that can be used.
i. Control Circuit
In order to control the combustion blower and gas valve in response to feedback,
some form of a controller must be chosen and implemented. There are many different
types of control circuits that can be used, depending on the cost, size, power usage,
and other factors.
ii. Internal Circuit Components
Several circuit components must be chosen and used to interface with the different
types of inputs and outputs. These components may be simple circuit elements such
as resisters, capacitors, and inductors; or may be third party integrated circuits that
provide functionality in a smaller, cost effective package.
iii. Board Layout
The layout of the circuit components and the connections between them can be varied
to meet the size and space requirements of the final package.
iv. Computer I/O Interface
An interface to program and monitor the control board must be selected and used to
meet the needed functionality. There are a number of different interfaces available or
a custom interface can be developed to meet requirements not met by existing
v. Graphical User Interface
A computer program must be created using a programming language and/or library to
allow the user of the control board to set parameters and monitor the operation of the
board. The programming language must be chosen based on provided features and the
vi. Control Algorithms
Software must be written to control the various hardware components based on
feedback from sensors and parameters given by the user. The algorithms can be based
on existing algorithms or created by the designer to meet the requirements.
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Section 1.4: Limitations and Constraints
The control system must follow the limitations and constrains that are outside the scope
of the defined parameters. These parameters include size and cost.
The size of the control must not exceed a length, width, and height of 5.75” X 3.3” X
1.5”, respectively. There is no minimum size required.
ii. Board Development Budget
Wayne Combustion Systems has allotted up to $3000 for development.
Section 1.5: Additional Considerations
There are other factors controlling the design of the control system. These factors must be
researched and understood before stepping into the design phase of the project. These
factors include safety and environment.
This system must be safe to use in the field and also comply with the RoHS directive.
The conditions of the surrounding environment of the board must be considered when
contemplating components that are compatible in conditions up to 85°C.
Section II: Conceptual Designs
The results from brainstorming were each researched. This research was then used to explain each
conceptual solution and to explain the advantages and disadvantages they each had. This part will help
when it comes time to make decision matrixes to determine the factors and the score each conceptual
solution will receive for each given factor.
Section 2.1: User Testing/Programming Software
Concept 1: Visual C++
o Good team experience with C++
o Lots of existing code
o No team experience with Visual C++
o Difficult to design
o Expensive IDE for future redesign
Concept 2: Java
o Free IDE for design/redesign
o Limited design team experience
Concept 3: Visual Basic
o Simple source code for GUI applications
o Moderate design team experience
o Language is not powerful
o Expensive IDE for future redesign
Concept 4: LabVIEW
o Designed for creating graphical test interfaces
o Good design team experience
o Built in protocols for USB, Serial communication
o Expensive IDE for future redesign
o Expensive application builder for test bench distribution
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Section 2.2: Microcontroller
The controller subsystem is responsible for implementing the control algorithms and logic
necessary for the board to correctly control the outputs and monitor the inputs. The program flow
can be implemented in any of these subsystems; they differ in their efficiency, performance, and
hardware features. These design concepts may be combined with the other subsystems to
produce the final design.
Concept 1: PIC32MX340F128LT
This design uses a PIC32MX3 series microcontroller from Microchip as the main controller.
This chip features a MIPS32 32-bit core with a maximum frequency of 80 MHz. It has good
support and has complete documentation and examples. It comes in many different
configurations with up to 512 KB of flash memory as well as 8 KB to 32KB of SRAM memory.
The chip also has built in support for serial over RS-232 and RS-485. Additionally, it comes with
4 built in PWM outputs.
Section 2.3: Computer I/O Interface
This subsystem is the communication interface between the computer and the board. It is
responsible for allowing the computer software to set board parameters as well as monitor the
Concept 1: Serial RS-232
This concept uses the RS-232 standard for communication between the computer software and
the board. The RS-232 standard is widely used in industrial applications and most
microcontrollers can be interfaced using RS-232. The standard defines the electrical
characteristics of drivers and receivers in a digital network.
o Simple to use on microcontrollers
o Easy to program
o Slower than other interfaces
o Most new computers not equipped with RS-232 interfaces
o May require purchase of RS-232 to USB for newer computers
Concept 2: USB
Concept 2 utilizes the USB standard for the physical communication layer between the computer
software and the board. The USB standard uses four wires for full duplex communication.
Virtually all-modern computers support USB and many microcontrollers contain an
implementation. Because USB is used for many other devices, the board may be expanded to
communicate with more devices for additional functionality. For example, a USB flash drive
may be used to flash the board software provided the microcontroller supports it.
o Widely supported on computers
o Able to provide more features by interfacing with other USB devices
o May be harder to use if microcontroller does not provide USB drivers
o Some microcontrollers support USB and provide drivers, negating the first
Concept 3: Ethernet
This concept uses Ethernet for communication with the board. Many protocols can be
implemented using Ethernet, such as TCP or UDP, depending on the microcontroller support.
Ethernet can achieve speeds of 100 or 1000 MB per second. Ethernet requires each device to
have a unique address, which can make setting up the connection more complicated than serial or
o Most computers have connectors
o Can provided embedded webpage for diagnostics
o Requires microcontroller support, not common
o Hard to program
o More complicated connection procedure
Section 2.4: Voltage Regulator
A voltage regulator is a piece of circuitry equipment that is designed to maintain a constant level
of voltage. This is used to reduce the input voltage of the system to the desired voltage that will
be used by the IC chips that control the outputs.
Concept 1: Series Pass Voltage Regulator
A series voltage regulator uses a variable element that is in series with a load. Then by changing
the resistance of the series element, the voltage drop across it can be varied to ensure that the
voltage across the load is constant.
o Most effective in high voltage systems
o Least expensive
o Voltage across the load remains constant
o Least effective in low voltage systems
o Power is continually dissipated