p09141 satellite thermal heater controller anthony berwin mechanical engineer scott rioux industrial...

P09141Satellite Thermal Heater Controller

Anthony Berwin Mechanical Engineer

Scott Rioux Industrial Engineer Greg Pawlowski Electrical Engineer Sarmad Abedin Electrical EngineerJohn Scipione Electrical

Engineer

Sponsors: ITT Corporation & D3 Engineering

1 Project Review R•I•TKGCOE Multidisciplinary Senior Design

Milestones MSD 1

January 16, 2009 – System Level Design Review February 13, 2009 – Detailed Design Review February 20, 2009 – MSD I Review Presentation

MSD II May 2, 2009 – Poster Session I May 15, 2009 – Technical Paper May 15, 2009 – MSD II Review Presentation May 19, 2009 – Demonstration May 22, 2009 – Poster Session II

Project Review R•I•TKGCOE Multidisciplinary Senior Design

2

Project Overview Description: Thermal Controller for Satellite

Operations Market: Space Systems Division of ITT Key Deliverables:

1. Power Efficiency 2. Mass 3. Performance 4. Communications 5. Cost


Project Sections Enclosure Graphical User Interface PC to Master Communication Master to Slaves Communication


EnclosureNeeds & Specifications Material (6061 Aluminum Alloy, 316 Stainless

Steel) Size (Minimize) Mass (<0.450 lb) Mounting (Enclosure, PCB, Connectors*) Vibrations (23.1 G’s Random Vibration) Thermal (-40°C to +55°C) Vacuum Environment

Ventilation* (<1 psi/s) Outgassing

Torque on Screws* EMI Leakage* (<100 kHz)5 Project Review R•I•TKGCOE Multidisciplinary Senior

Design

EnclosureAssembly Model


EnclosureAssembly Model: Exploded View


EnclosureSpecifications Met Material:

6061-T6511 Aluminum Alloy (Top & Bottom Parts) Type 316 Stainless Steel (Machine Screws)

Total Size: 3.50” x 2.875” x 1.00” Size of the PCB with the Accelerometer: 3.0” x

2.0” x 0.563” Total Mass: 0.4317 lb

4.06% below the 0.450 lb limit Enclosure Mounting:

Flat Plate & Cylinder (R > 18”), dmax < 3/32”

PCB Mounting: Five (5) 2-56 Machine Screws


EnclosureSpecifications Not Met Partially Met

Connector Mounting Vacuum Environment

Ventilation Outgassing

Not Met Torque on Screws EMI Leakage


EnclosureDesign Analysis: Strengths & Weaknesses Strengths

Scalable to Varying Sizes of the PCB Easy to Machine Two (2) Pieces Low Cost of Materials Easily Assembled

Weaknesses Excess Weight

1/8” thickness for machining Connector Mounting

Mating connectors are not secured


EnclosureDesign Analysis: Potential Improvements

Decrease Weight Decrease the thickness to 1/16” or 3/32” from 1/8” Change the strew type from 4-40 to 2-56

Connector Mounting Add component to secure mating connectors

Account for Ventilation Add ventilation slot

Account for EMI Leakage Minimum thickness

Account for the Torque on Screws Verify minimum screw type


Graphical User InterfaceOverview System required a simple computer interface Needed to be able to control DSP’s and send

commands Easily readable and intuitive Be able to control multiple parameters Be able to communicate via Serial Port Able to control 256 DSP’s


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Graphical User InterfaceLabView LabView was chosen mainly because of its

ease of use, and familiarity between the team members

LabView allows us to easily create a nice GUI with multiple features

LabView is also scalable, allows us to add or change features easily without rewriting all of the programming


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Graphical User InterfaceSpecifications Communicate over serial port (RS232) Ability to see heater state status and

telemetry information Ability to set and change temperature set

points Ability to chose between 255 slaves to upload

temperature


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Graphical User InterfaceProgramming Programming started with communication

over serial Building blocks for the project were added on

top Each requirement or functionality that was

needed was researched then implemented Problems that arose were quickly dealt with by

research


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Graphical User InterfaceProgramming/Development Message Creation

Messages were created using loops and numerical to string identifiers.

Labview sends out 24 bits, which gets converted to 3 ASCII characters

Message Contents Message contains all elements needed to

communicate with DSP Slave ID gets transmitted first, control bits 2nd, and

temperature last The control bits relate to controls on the front panel

that allow the user to manipulate the message and retrieve different data


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Graphical User InterfaceProgramming/Development


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Structures All Labview programming is grouped within loop

structures so data and set points can be updated continuously.

Different structures exist for different functionality. Initialization of slaves, Continuous message

sending, Message building Some key building blocks are : Steinhart-Hart

function, Binary number creation, Voltage readings, Serial port open/close

Graphical User InterfaceFront Panel


Graphical User InterfaceSpecs Met/ Not Met


Met Ability to communicate over serial Ability to send and receive data from DSP Ability to control temperature and control bits Has visual indicators

Not Met Simplicity of GUI

Graphical User InterfaceStrengths/Weaknesses


Strengths Very Powerful Has lots of Error Checking and Debugging Easily Understood

Weaknesses Computer resource intensive Complex changes take time

Graphical User InterfacePotential Improvements


Improvements Make front panel more visually appealing Revise and improve looping Create simpler ways to do programming

CommunicationsOverview


PC to Master Communications Overview Communication between Master DSP and

Graphical User Interface (GUI) must occur over SCI Protocol must be able to incorporate the many

needs of the User Master must generate a new message for the

‘slave’ DSPs after receiving a message from GUI. After receiving a response from the appropriate

slave, the master DSP must generate a new message to send back to GUI


PC to Master Communications SCI Protocol SCI protocol (LabView to Master)

3 Pins - Transmit, Receive, Ground 3 Transmissions - 12 Bit Each 1 Start Bit 8 Data Bits(Slave ID, Temp. Bits, and Ctrl Bits) 1 Parity Bit (Eliminates Checksum) 2 End Bits


PC to Master Communications Objectives The SCI message was received and transmitted

back using an interrupt routine using the RX buffer and TX buffer in the EzDSP.

A circular buffer routine was utilized to prevent overriding incoming messages from LabView.

The Master to DSP message also included five telemetry pins, mainly used for debugging.

Messages from LabView were appended to include start bits, transmit/receive bit, error bit, and check sum bits.


PC to Master Communications Specifications Met/Unmet Specs Met

Ability to communicate from/to GUI via serial port Ability to communicate to/from the slaves and to

retrieve information from the HHC The use of an interrupt service routine for

transmitting and receiving Unmet Specs

20ms total communication time


PC to Master Communications Strengths and Weaknesses Strengths

The user can continuously ask the master to report data from any particular slave and see it updating in real time.

The protocol is reliably able to handle all of the user’s needs.

Weaknesses Cannot guarantee a complete and/or correct

message is sent all the time because of SCI TCP for example, has the ability to automatically

resend messages to ensure proper transmission to the receiver.


PC to Master CommunicationsPotential Improvements A more reliable protocol instead of SCI

In order to better handle errors and ensure proper transmission


Master to Slave CommunicationNeeds Master DSP communicates with up to 256

slaves over the heater power bus. No dedicated communication lines are used.

One master, multiple slave design. DSPs communicate by a half-duplex BFSK

technique.


Master to Slave Communication Modulation/Demodulation A sine wave is generated from a binary string

using the HRPWM and a passive low pass filter.

The sine wave is transmitted over the DC power bus.

The sine wave is then demodulated back into binary using the ADC with a digital filter.

The Goertzel Algorithm was used to implement the digital filter.


Master to Slave CommunicationProtocol BFSK Protocol (Master to Slave)

Bi-directional, half-duplex (only slave or master can talk at one time)

Bit by bit transmission Different frequencies for ‘1’ and ‘0’ (in order to

meet the 20 ms spec, min. freq = 5kHz; 200 us/bit)

‘0’ frequency = 62.5 kHz ‘1’ frequency = 78 kHz No activity on line means no signal


Master to Slave Communication Protocol 40 Bit Transmission

2 Start Bits 6 Checksum Bits 12 Data (temp) Bits 6 Control Bits (read/set, temp/htr state, etc.) 5 Telemetry Pins 8 Bits for Slave ID 1 End Bit


Master to Slave Communication Interface Electronics Coupling transformer to couple to AC and DC

components. Capacitor along with transformer used to

create a high pass filter. Allows us to create a sine wave on power bus

without disturbing the operation of the heaters.


Master to Slave Communication Strengths and Weaknesses Strengths

Used software techniques in the DSP to do the modulation and demodulation rather than using external hardware.

Flexible: different frequency/bandwidth combinations possible.

Weaknesses Each slave added creates a parallel resistance so

a larger and larger signal is needed for each slave added.

We don’t check to see if a message is good until a complete message is received.

Half Duplex only, can only send or receive at one time.

Reliability could be improved.34 Project Review R•I•TKGCOE Multidisciplinary Senior

Design

Master to Slave Communication Specifications Master to slave communication time 20ms

Did not meet, actual communication time ~200ms

Bandwidth < 300KHz Met, Bandwidth < 90Khz

Bit error rate 1e-6 Did not meet, ber undermined but higher than

1e-6 Signal to noise ratio -40db

Did not meet, snr is around 10db Amplitude < 10mVpp

Did not meet, Amplitude ~ 1Vpp35 Project Review R•I•TKGCOE Multidisciplinary Senior Design

Master to Slave Communication How could these be improved? Master to slave communication time 20ms

Reduce code size by splitting up master and slave code

Used external hardware to generate and detect sine wave

Bit error rate 1e-6 Improve synchronization between master and

slave Goertzel. Signal to noise ratio -40db

Longer transmissions per bit, raise the bandwidth

Amplitude < 10mVpp Output smaller signal and then amplify it


Closing Comments Special Thanks

Margaret Bailey, Jerome Barczykowski, Sohail Dianat, Christopher Hoople, Marca Lam, Chuck Moon, Jay Radhakrishnan, Scott Reardon, George Slack, Perry Voyer, Christianna Walter and John Wellin

Questions and/or Comments


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p09141 satellite thermal heater controller anthony berwin mechanical engineer scott rioux industrial...

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