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TD-98-

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TD-98-

    TD-98-049

    Patrick Shaw

    8/3/98

    Strain Gauge Calibration Program for the LTL

    Operations Manual

    Table of Contents

    Introduction …………………………………. 1-1

    System Requirements …………………………. 2-1

    Entering Gauge Info …………………………. 3-1

    Saving Data to a File …………………………. 4-1

    Current Check …………………………………. 5-1

    Performing a Calibration Run ………………… 6-1

    Liquid and Temperature Check ………………. 7-1

    Setting-Up for a Calibration Run ……………… 8-1

    Sample Calibration Run on LTL ……………… 9-1

1-1 Introduction

    This program was designed to allow for the calibration of both beam gauges and

    bullet gauges. Each data reading consists of a pressure value and the corresponding

    resistance at that pressure. This data is saved to a file, as well as being displayed on the

    monitor.

    To boot the program type CALSG at the C:\ prompt. All the data is saved to a directory defined by the variable pathspec$. This variable can be changed in order to create a new directory in which to store calibration data. The variable pathspec$ can be

    accessed in the main module of the program.(Once changed the program must be re-

    complied).

2-1 System Requirements

     This program was designed to run with the following devices.

    ? HP 3548A multimeter

    ? Keithley 706 Scanner

    ? Keithley Model 220 Programmable Current Source

    3-1 Entering Gauge Info

     Once the program is started, the user will be presented with the following screen.

What type of gauge(s) is(are) to be calibrated ?

    Choices are :

     HGQ-Inner (HI)

     HGQ-Outer (HO)

     LBQ-Inner (LI)

     LBQ-Outer (LO)

     Bullet (B)

    Gauge type?

     At this point the user must select a gauge type. Once the gauge type is selected

    the type of gauge and the area of the gauge is stored by the program.

    Once the gauge type has been entered the user is prompted by the following

    statement.

Number of gauges to calibrate?

     At this point the user must enter the number of gauges to calibrate. At this

    time(8/3/98), the system allows either two strain gauges or four bullet gauges to be tested

    at one time.

     After the user has entered the number of gauges to calibrate he/she is asked to

    confirm the selection.

     Following confirmation of the number and type of gauges, the program asks the

    user if the calibration run will be a warm run(300K) or a cold run(4.2K).

    4-1 Saving Data to a File

     After the program has allowed to user to determine the type of gauges to be

    calibrated, the program displays the following.

    Do you want to save data to file

    At this point the user enters a Y or y for yes or a N or n for no. If the user enters

    yes then he/she will be allowed to enter a line of comments to be included with the file.

     The file is saved in the directory specified by the variable pathspec$. This

    variable can be found in the main module of the program.

     If the user enters file name that already exists in the directory, the user will be

    promptly notified with the following.

     File already exists. Overwrite?

     Answering Y or y overwrites the existing file. Entering an N or n causes the user

    to be asked to enter a different filename.

    5-1 Current Check

    Keithley 220 Current Source Operating Parameters Once the filename of the run has been entered and accepted, the program will display the following.

    This statement will be followed by a description of the current being supplied and

    the voltage limit set on the current source. If the value for the current reads 0 mA, then the operator must check the wiring of the gauges. Make sure that all connections are

    either connected to a strain gauge or properly jumpered.

    Once done the operator should continue to the point where he/she can take a measurement. A measurement should then be taken in order to confirm that the system is

    working properly.

6-1 Performing a Calibration Run

     Once the task of setting up the run has been completed, the operator is ready to

    start taking data. Data is displayed to the user as depicted below.

    The calibration procedure is as follows.

    1. At the beginning of a calibration run, the user will see that two values are displayed

    for the current load provided by the LTL. These values are labeled LOADUP and

    LOADDOWN. The user need only be concerned with the LOADUP value as long as

    the force applied is increasing. At the point in the calibration run that the load applied

    begins to decrease, it is necessary for the user to concern him/herself with the

    LOADDOWN value.

    2. Once the desired value of force is achieved and the load has become fairly stable, the

    user can press any key to take a reading.

    3. The program then stops updating the current load, and begins the process of taking

    voltage measurements on each gauge channel.

4. Once the user has completed a calibration run, he/she can press Q or q to end the

    program.

    7-1 Liquid and Temperature Check

     At any time during a cold calibration run the user can press T or t to check the

    temperature in the dewar. This temperature is given in degrees Kelvin. The command

    also updates the percentage of liquid remaining in the dewar.

     If the temperature in the dewar rises above 4.55 degrees Kelvin then the program

    will display an error message in the lower right hand corner of the screen. If the liquid

    level is below 25%, a similar error message will appear.

     Note: Two temperatures are displayed on the screen. Each value represents a

    different thermometer in the dewar. Both value should read very close to each other. If

    the values differ by more then a few milli-Kelvin, then the user should make sure to

    check the thermometers before the next run.

    8-1 Setting-Up for a Calibration run

     This section has been included in order to outline the basic procedure used to

    prepare for a strain gauge calibration run.

    1. All push-pins on the LTL must either be connected to a strain gauge or be

    appropriately jumpered. Make sure to note which channel each gauge is

    attached to.

    2. The diagram below depicts the proper alignment for strain gauge wires to the

    push-pins.

    3. Boot the program(CALSG) and follow the appropriate steps until able to take

    a reading. Take a reading to make sure that all channels are reading as

    expected.

4. Secure base plate to LTL and turn on LTL.

    5. Determine point of contact between test fixture and ram. Back the ram of the

    fixture by at least .5 inches. Note this position and use it as the zero-point for

    all data runs.

6. Proceed with calibration until its conclusion.

    9-1 Sample Calibration Run on the LTL

    1. Once gauges secure, the operator can begin the procedure to calibrate the

    gauges.

    2. If a cold calibration is being performed than the user must begin to cool the

    gauges to 4.2 K. Once the gauges are at 4.2K and the liquid level is above

    25%, the user may proceed.

    3. Before collecting data, the operator should train the gauges to 7 times to 17k.

    This must be done both warm and cold.

    4. At this time(8/10/98), the procedure is to take points, while the gauges are

    being loaded, from 0-14,000 lbs at every thousand. The gauges are then

    unloaded to zero, taking points in a similar fashion.

    As points are recorded the user should try to maintain no more than a 20

    lbs. shift in the load over the period it takes for the program to obtain data for

    the gauges. Be certain that, when loading, the force is always increasing as a

    reading is taken. In turn, when unloading, be sure that the readings are only

    taken as the force applied is decreasing.

    Note: The zero points at the beginning and end of a cycle do not

    correspond with zero on the screen. Instead, the user should determine the

    position at which the fixture comes in contact with the ram. This position can

    be determined using the LVDT., To be sure that the gauge is not under any

    pressure, make sure the ram is at least .5 inches above the point at which it

    makes contact with the fixture.

    5. Once the user has completed one cycle, he/she repeats the process twice more.

    Gauges must be calibrated both warm and cold.

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