The Control Unit for the TTA is a standard half rack mount size with dimensions of 8.5"x8"x3.5" (WxDxH). All connectors with the exception of the power switch are located on the front of the unit. The TTA control electronics chasis can be seen below.

1. Power Connector - The power connector is a circular metal connector with 17 pins for applying the heating voltage to a cell. The TTA ships with a custom 20 foot cable with a matching connector on the TTA end for the power delivery.
2. Sense Connector - The sense connector is a standard female micro DB50 SCSI II connector, as is the connector on the array end. The TTA ships with a 20 foot male to male SCSI II cable, but any male micro DB50 to male micro DB50 SCSI II cable can be used.
3. External Voltmeter - A standard female BNC connector provides the connection for reading a -10 to 10 volt analog voltage from an external device such as a pressure transducer.
4. External Trigger - The top female BNC connector is the external trigger input, and should not be confused with the external voltage connector.
5. Serial Port - The serial port on the TTA uses a PS2 connector and requires a custom DB9 to PS2 cable that will be shipped with the TTA.
6. Power LEDs - The green LEDs indicate the status of the logic and heating power supplies.
7. Status / Communications LED - The red LED above the serial port will continually flash at about 4Hz while the TTA is properly booted and ready to accept commands from the PC. This flashing will be interrupted and the LED will temporarily remain on or off while accepting and processing a command and transmitting data to the PC.
8. Power Switch - Turns the TTA on or off.

The following cables are sent standard with the TTA.

Below is an example of what a TTA sensor array might look like. The frame is made of steel stock, with the tungsten wires strung between. The electrical wiring is soldered to the frame and terminates in a 3 foot long tether which has connectors to mate with the power and sense connectors from the TTA electronics.

If multiple arrays are to be run simultantously, an break out box will be requred to interface the TTA cables to the array tethers. This is a small aluminum enclosure with TTA interface connectors on one side and array interface connectors on the other. This box will be customized to the number of arrays running. In general, the arrays will have to be located so that all the tethers can reach the breakout box.

Shown below is the TTA Comm interface for the Thermal Transient Anemometer with various elements numbered for reference.

1. Flow Rate pane – all information pertaining to the air speed through a cell will be displayed here.
2. Temperature Pane – all information pertaining to the temperature of a given cell will be displayed here.
3. &  4.  Cell – each cell has a block in each information pane. The blocks will vary in color depending on the flow speed or temperature of the cell. Clicking on a cell’s block will activate or deactivate it. Inactive cells will be changed to grey. Right clicking a cell's block will pop-up a menu of single cell functions.
5. &  6.  Cell Data – the numerical representation of the air speed or temperature of a given cell also shown by the color of the associated block.
7. &  8.  Cell Scale – shows the color for minimum and maximum flow / temperature. Clicking on the color bar will allow the user to change the colors and clicking on the number will allow the minimum and maximum to be adjusted.
9. External Voltage – shows the voltage ranging from -10V to 10V from the external input from a device such as a pressure transducer.
10. Connect Button – opens a communication link to the TTA, this must be done prior to any commands or data being sent to or from the TTA. The button will be red if the TTA is disconnected and will turn green once connected.
11. Atmospheric Pressure - must be set by the user when taking data in order to compensate for temperature in the velocity measurements.
12. Save to File – when cycling the cells, indicates whether or not the data will be written to a file.
13. Number of Cycles – selects the number of cycles to run. A value of zero or any non-numerical value will loop until the user manually stops the TTA.
14. Start Cycle – will measure each cell sequentially, starting over at the end of the array until the preset number of cycles is reached.
15. Start After Trigger – will wait for the external trigger, then start taking flow and temperature data as if the user had clicked the Start Cycle button.
16. Time Indicators - will show the time in minues and seconds for the most recent Cell run, the total for the current cycle and the total for the entire Run.
17. Clear Data Button - will clear the current displayed data. This does not affect the data to be writen to a file if file output is enabled.
18. Status Bar – gives information about the different aspects of the program when the mouse is hovered over them. Also gives status information while the TTA is cycling.
19. Progress Bar – shows the relative progress of a set of cycles if the number of cycles box is set to a finite number.
20. Status Log – the 500 most recent status updates will be displayed here until it is cleared. The status log can be shown or hidden through the View menu by choosing View GUI Log.
21. Pause Log Button – stops the Status Log from being updated. The most recent status update will still be shown in the Status Bar
22. Clear Log Button – clears the Status Log.

File Menu

• Connect to TTA – serves the same function as the Connect button on the main GUI window attempting to communicate with the TTA on the chosen serial port at a variety of baud rates. Will change to Disconnect once a connection is established.
• Load TTA Setup – Loads values such as baud rate, sample number and sample frequency from a file.
• Load TTA Calibration – loads a calibration for the TTA from a file. This file will be included with the TTA and includes the information necessary to perform accurate resistance and voltage measurements.
• Load Array Calibration – loads the calibration for a specific array of up to 32 cells from a file. This file will be included with any TTA array and includes the information about the individual tungsten wires necessary to calculate overheats, temperatures and air flow.
• Save Array Calibration - saves the updated array calibration to a file after updating the cold resistance values of the array.
• Select Output File – allows the user to choose the file for data output.
• Set File Number – allows the user to set up automatic numbering of sequential data output files. This option will be enabled after a data output file is chosen.
• Delimiter - allows the user to set the delimiter used in the data file. Options are a space, tab, or comma.
• Exit – closes the program.

Settings Menu

• Board Setup – opens the board setup window where baud rate, sample number, sample frequency, and overheat can be specified.
• Comm Port - allows the selection of the serial port being used ports 1-4 are currently supported. This menu option is only active when the software is disconnected from the TTA.
• Comm Mode - allows switching between verbose mode where all data is returned to the PC (slower) and smiple mode where only the processed result is returned (faster). This option is only active when the software is actively connected to the TTA.

Cell Menu

• Cell Order - opens the cell order window where the user can customize the order in which the cells will be run.
• Get Base Resistances - re-acquires the cold resistances for the wires as done in calibration. This can help eliminate any drift in the wire resistances over time without requiring a complete recalibration.
• Cycle Resistances - cycles through all active cells once and displays the current resistance in the temperature pane. No file is written for this option even if file output is chosen.
• Cycle Temperatures - cycles through all active cells once and displays the current temperature in the temperature pane. No file is written for this option even if file output is chosen.
• Cycle Velocities - cycles through all active cells once and displays the current velocity in the velocity pane. No file is written for this option even if file output is chosen.

View Menu

• Show Comm Log - opens a separate window showing all serial port activity for debugging purposes and tech support.
• Show GUI Log - extends the bottom of the GUI window to show a log of recent commands issued.

Communications Port Selection

TTA Comm does not automatically connect to the TTA upon launching. Before any commands can be sent and data received, the user must connect to the TTA. TTA Comm uses one serial port, generally this will be Comm 1 or Comm 2, but ports 1 through 4 may be chosen from the settings menu as seen to the right. Com 1 will be chosen by default the first time the program is run, and if the correct port is not known, it is recommended to start with Comm 1 and work from there.

Communications Attempts

Once a Comm port is chosen, clicking the Connect button will attempt to communicate with the TTA on the chosen port. On power up, the TTA will initially be set to Comm settings of 115200, 8, n, 1. It is recommended that the baud rate be left at 115200bps, but multiple buad rates from 9600bps through 115200bps are supported. The baud rate can be set under the Board Setup item in the Settings menu.

In the event that the baud rate is changed from the default and either TTA Comm or the TTA hardware is subsequently restarted, it is possible that the TTA and the PC will not be at the same baud rate. To account for this chance, if TTA Comm is unable to communicate with the TTA at the currently set baud rate, it will then scan through the other allowable baudrates looking for one that does work.

During the process of establishing communication with the TTA, the Connect button will be changed to Abort. Clicking the Abort button will cause TTA Comm to cease it’s attempts to communicate with the TTA. Upon successful connection, the Connect button will be change to Disconnect and the background color will change to green indicating a successful connection. A successful connection will also enable the parts of the GUI which send commands to the TTA such as the Start Cycle and Start After Trigger as well as the cell speicific right click menus.

TTA Settings Window

The TTA setup window as seen at right can be accessed through the Settings menu under Board Setup. For general use, these settings will not require modification; however controls specific to the TTA control box can be set here if desired.

1. Number of Samples (decay)- sets the number of A/D samples that are taken during the thermal decay. A setting of less than 300 will result in a warning window that the number of samples may be insufficient for reliable data. Acquisition and transfer of the sample data does acount for a non-trivial portion of the time taken to cycle a cell, and it should be kept in mind that increasing the number of samples will result in a longer cycle time. The number of samples is limited to 9999.
2. Sampling Frequency (decay) - sets the frequency that the chosen number of samples is taken at. If the sample frequency is set below 2000 samples per second, a warning window will be shown with a warning that the frequency might be insufficient to capture the desired data from the thermal decay curve. The frequency is limited to 9999.
3. Overheat - sets the wire overheat that the TTA will attempt to reach for all wires. This is a maximum, and may not be reached under higher flow conditions.
4. Numer os Samples (voltmeter) - sets the number of A/D samples that are taken when checking resistance and external voltage. A setting of less than 300 will result in a warning window that the number of samples may be insufficient for reliable data. Acquisition and transfer of the sample data does acount for a non-trivial portion of the time taken to cycle a cell, and it should be kept in mind that increasing the number of samples will result in a longer cycle time. The number of samples is limited to 9999.
5. Sampling Frequency (voltmeter) - sets the frequency that the chosen number of samples is taken at. If the sample frequency is set below 2000 samples per second, a warning window will be shown with a warning that the frequency might be insufficient to capture the desired data from the thermal decay curve. The frequency is limited to 9999.
6. Baud Rate - the baud rate at which the chosen comm port will operate. Higher baudrates allow faster operation but have a higher potential for errors. If the TTA often looses communication with the software, reducing the baudrate may remedy the situation.
7. OK button - applies all settings and closes the settings window.
8. Apply button - applies all settings and leave the settings window open.
9. Cancel - discards all settings and closes the settings window.
10. Save to File - opens a file dialog, allowing the user to save a custom TTA setup file. The file will be formated as plain text and is user readable, but should not be directly edited since the exact formatting is important for loading the setup at a later time.
11. Load Defaults - will load the default values into the setup window. If a defaults file is found, the values will be used. If not, hard coded defaults in the software will be loaded.
12. Save as Defaults - will save the settings shown to a file named "DefaultSetup.txt" in the program folder. This file will then be loaded on each subsequent start of TTA Comm.

Setup Notes

• Experimentally, the wires have been found to return to ambient temperature after approximately 150 to 400 milliseconds at zero flow. The default number of samples and sampling frequency has been chosen to match this time. In general the number of samples divided by the sampling frequency (for decay) should be kept between 0.15 and 0.5. Other combinations may result in either insufficient or excessive data.
• When in verbose mode, there is a limit on the number of samples that can be returned due to the comm speed. At 115200bps and 5kHz sampling the TTA can take a maximum of 2400 samples. This is not a perfectly defined relationship, but in general verbose mode should be reserved for running at high comm speed. At 10kHz the TTA can take a maximum of 1280 samples in verbose mode. This limit does not apply when using the simple (processed data only) return mode.
• Overheat should be kept below 2.0. Due to the nature of the overheat sense, this is not an exact number but instead a minimum. If this minimum is not met after a preset time delay the TTA will quit overheating the wire, sample during the decay and return the data collected. The software will account for this when calculating 1/Tau.

TTA Cell Selection

In the TTA Comm GUI, each rectangular block represents one cell of the array. Each block is also a button. Clicking the block will toggle the activity status of the cell. If active, fill color of the cell will correspond to the last data measured for that cell. Inactive cells will be shown in grey. The status of a cell does not affect the cell order, it simply causes the cell to be skipped when it’s turn arrives. Deactivating cells will shorten the cycle time for the remaining cells, allowing a subset of the array to be run faster than the full array. Cells can be activated or deactivated without stopping the current cycle of the TTA but this will cause a non-uniform data file if file output is enabled.

TTA Cell Order

Upon loading, TTA Comm is set to run the cells sequentially starting with cell 1 and ending with the highest numbered cell in the array. Arrays are generally ordered left-to-right, top-to-bottom. In the case that this orderis not desirable, the TTA is capable of running cells out of the standard sequential order.

The array cells can be reordered by choosing Cell Order from the Setting menu which will bring up the window to the right. Upon loading, the current cell order will be shown. Active cells will have a white box, while inactive ones will be grey. By changing the numbers shown below each cell, the cell order can be redefined. Each cell must have a specified order, even if it is inactive at the time. Re-ordering the cells is a matter of swapping orders. When a number is changed for a cell it will automatically swap order with the cell currently using the number. Attempting to enter a value outside the range of cells or an erroneous value will cause the cell to retain its current order.

Using Figure 7 as an example, cells 1 through 8 would be run in reverse order. Cells 9 through 16 are deactivated and thus regardless of order, will not run. If cells 9 through 16 were later activated in the main GUI window, they would run in sequential order. If any of cells 1 through 8 were later deactivated, they would be skipped, but the rest of the cells would continue to run in order. If Cell 8 were changed to be 3rd in the running order, then Cell 6, which is currently 3rd would be changed to running 1st.

Summary of Calibration Data

Calibration is done prior to the TTA and accompanying array being shipped. Due to the properties of the tungsten wires, the TTA should never need recalibration by the end user. There are two independent calibration files one specific to the TTA control box and one specific to the set of TTA wire arrays being used. The TTA specific calibration does not need to be changed to run different arrays. All files which hold calibration or settings data are saved in plain text format. Upon loading, the file is checked to contain a proper header and the correct amount of data. If the file appears to be invalid, the user will be warned and the calibration data will not be loaded.

Loading Calibrations

Default

The set of calibrations which go with the original TTA control box and array will be stored in the install folder for TTA Comm as DefaultTTACal.txt and DefaultArrayCal.txt. These files will automatically be loaded upon starting the TTA Comm software. Alternative calibrations do not need to be loaded unless the TTA control box or TTA arrays are not those originally shipped with the software being used. In the case that the TTA electronics are shipped with multiple arrays, one of the array calibrations will be set as the default an alter nate calibration will have to be manually loaded if the other array is to be used. If it is preferred that no array calibration is loaded, the DefaultArrayCal.txt file may be removed from the program folder or renamed.

Manual

If the default files are not present, or contain undesired information, the user can load alternative calibrations through the GUI’s file menu. This will be necessary if different arrays are to be used on the same TTA control box. The calibrations are stored as plain text files, but the GUI will check to ensure that they contain a proper header and the correct amount of data, and will warn the user if the file was invalid. All calibrations are loaded from the file menu and will display the new information in the GUI log if loaded correctly.

Cycles

A cycle is defined as a complete run through all active channels acquiring both temperature and flow data. The Start Cycle button (4) will start the cycle. Once the TTA is cycling, the Start Cycle button will change to Abort. This will interrupt the data acquisition after the next full operation is complete. It will take a short time to abort a run. Barring action by the operator, the TTA will continue running until the number of cycles listed in the box marked 3 is reached. Entering 0 cycles, or any non-numeric character will cause the TTA to cycle continuously until stopped by the user. Durring a cycle the time data will be displayed in area 6.

Data Format

There are two methods by which the user can retrieve data from the TTA, displayed in TTA Comm or through an output file.

GUI Display

As the TTA cycles through the attached cells, the data for each cell is updated and will be displayed until the next time the cell is cycled. Temperature and flow data will be displayed both as a number and through the coloration of the block corresponding to a specific cell. This output method is constantly running even when file output is being used. This data can be cleared by clicking the Clear Data button, numbered 7 above.

File Output

File output can be obtained by checking the Save to File check box (2) prior to starting a cycle. The file for output can be chosen through the File menu, or if not chosen, the user will be prompted when the TTA cycle is started. After choosing the file, the user will be prompted with the window seen at right. Once the file number and digits to be used are set, TTA Comm will automatically increment the file number and store the data from each sequential run in a new file. If the number of runs exceeds that allowed by the chosen number of digits, TTA Comm will wrap back to 0 and overwrite the old files. If the file chosen already exists the "Next file:" indicator will be hilighted in red as a warning.

The output file will be a text file formatted as delimited values. The user may choose the delimiter as a space, tab, or comma. The first line in the file will contain headers for all columns of the file, but may not line up exactly due to length differences between the headers and data. Each subsequent line in the file will correspond to the running of a single cell. As can be seen in the sample data file, the format will follow:

Cycle #, Cell #, Timestamp, Wire Ambient Resistance, Temperature, Wire Overheat Resistance, Overheat Temperature, 1/Tau, Velocity.

Sample Run

The GUI window seen below shows how the interface might look after running the first two cells through three cycles. The results of the most recent cycle can be seen in the coloration of the blocks and the numerical data below them. The sequence of events can be seen in the status log at the bottom of the program.

This section will run through the order of operations required to take data with the TTA. It is assumed that the default setup is being used, and will not go into technical detail about any settings or options.

1. Check Calibrations - Upon execution, the software will attempt to load a default set of calibrations. If these calibrations are loaded successfully, the GUI log will appear as shown in the screenshot above near the number 1. If the GUI log is not showing, it can be enabled by selecting Show GUI Log from the View Menu.
2. Load Calibrations - If all calibrations were successfully loaded, this step can be skipped. If one or more of the calibrations was not loaded, the user must load it in order to acquire data. This can be done from the File menu (numbered 2 above). All calibrations are stored as text files, but the contects of the file will be verified prior to loading any values. Clicking any of the Load options from the File menu will bring up a file dialog box. From here the user must find the calibration file for the TTA and Array being used. By default, these files will be installed in the same location as the TTA Comm program. They are also included on the CD or Zip file that accompanied the TTA.
3. Atmospheric Pressure - Entering the current atmospheric pressure in inches of Mercury will give the most accurate data from the TTA. If this information is not available, the default or reasonably close value will have minimal effect on the overall measurement.
4. Connect to the TTA - Clicking the connect button will cause the software will attempt to establish communications with the TTA at a pre-determined set of baud rates. The button will turn green and the label will change to Disconnect once a successful connection has been established. A successful connection will also enable all buttons and menus which send commands to the TTA.
5. Select Cells - by default all cells will be enabled. If this is not desired, cells can be disabled by clicking on either the Velocity or Temperature color swatches.
6. Enable External Voltage - by default the external voltage sampling is disabled, but can be enabled here (number 6 on screenshot) prior to starting a cycle.
7. Save to File - checking the save to file box will cause all subsequent data to be saved to consecutively numbered files.
8. Select Number of Cycles - this is the number of cycles that will be run and sent to a file each time the Start Cycle button is clicked.
9. Choose File Name - under the File menu, the user can set the next file name and number. If this is not done, the user will be prompted for this information prior to the first cycle.
10. Start Cycle - Clicking the Start Cycle button will read temperature and velocity from each cell, cycling through the entire array. The TTA will continue cycling until the number of cycles is reached.