Table of contents

*      Introduction

 

*      The New NMR.vi Program (Front Panel)

*      Fourier Transforms Settings panel (FFS Panel)

*      Korringa Temperature Measurement Program (KTM Panel)

*      Tip Angle Program

 

 

 

 

Introduction

 

            This manual describes some of the features of the Pulsed NMR Thermometer software developed in the Packard Group (Development of a Computer-Based Pulsed NMR Thermometer). The program was written in the software Lab View version 6.1 and was used to communicate with the National Instruments PCI-6115 data acquisition board (DAQ board). This software and the DAQ board are used in the Packard Group to make measurements of the temperature in systems with very low temperature (millikelvin). One of the main characteristic and advantages for us was that Lab View uses graphical programming instead of text-based programming.

            The idea behind making this software was to use the DAQ board and the instruments that we had in our laboratory to measure the NMR signal in a more systematic way. In addition, the procedure we followed to obtain the NMR signal was specific to the designs of our experiments. Therefore, you will find in this manual many features that are not useful for your particular experiment. However, we believe that there are general characteristics in this software that could be helpful to the Low Temperature community.  On the other hand, if you have our NMR software you also have the diagrams of the Lab View programs that we made. We encourage you to make all the modifications that you think are necessary to the program. The main purpose of putting our software on the Web is that the Low Temperature community could use this software in some extent.

            There is more information about the design of our experiment and how it was used with this software in the Packard Group’s website. In the same webpage that you download the NMR software, you can read three other guides.

  1. A Short Guide to our Pulsed NMR Thermometer by Hobeika
  2. A PDF file called Pulsed NMR thermometry by Hobeika
  3.  Development of a Computer-Based Pulsed NMR Thermometer by Hobeika et al.

 

            In case you need to know a little bit of the electronics we used we post the electric diagram of the Pre-amp that we used to increase the signal of the NMR response.  The diagram is in the webpage where the NMR software is.

 

            If you have any question or comments about this manual contact:

 

Rodrigo Castillo-Garza

 

            If you have any technical question about the software, design of the experiment or type of experiment in which this software was used. Contact:

 

Prof. Richard Packard

 

 

 

 

Good luck!

August 29, 2003

 

 

 

The New NMR.vi program (front panel)

 

Description of the front panel

 

Note: To follow this manual you need quick and continuous access to the NMR software.

 

The front panel consists of four charts, several indicators, and controls. In the following document, we will be describing the function of each button, control, etc. In addition, we will explain where to find the files of the NMR program, as well as where to find the data saved when the program is in use.

The main program of this software is The New NMR.vi.  It can be found at the following locations:

 

1.      If you are in the Packard group:

In the computer called “Nmr1” at “Data D:)/NMR Program”, so the complete path should be: Data D:)/NMR Program/The New NMR.vi

 

2.      If you just find yourself with this software:

You have to open the software Lab View, and then open the file “The New NMR.llb”. You can do this by clicking on the following icon.

After clicking it, a File Dialog will pop up asking what VI you want to open. You will have two options either you browse for the file “The New NMR.vi” or you write this name in the corresponding slot.  

After opening The New NMR.vi a window similar to the following should appear on the screen.

Figure No. 1. Pulsed NMR thermometer front panel.

 

 The controls modify the excitation, quenching, enable, and the acquisition of the data by the DAQ board. The screen has the controls and indicators of these parameters at the top, and we will call this part of the screen the parameter panel. At the far left, you will find buttons with different names (korringa, shot, spin echo).  The purposes of these buttons will be explained later. The charts occupy most of the space of the front panel, and each one of them will graph different data. Finally, at the bottom part of the screen you will find the controls and indicators of the LCMN Thermometer (which in our case was used with the Pulsed NMR thermometer) and some directory slots to write the path to which files have to be saved.

            The next picture will familiarize you with the pulses that are created by the DAQ board and the signals that it obtains due to the system.

            The first pulse from the top is what we call the excitation pulse. This pulse will put a voltage into the system. We called the second pulse the quenching pulse. The third one the enable (or Preamp-enable) and the last one is NMR signal (or FID).

            The reason we need all these pulses before we get the NMR signal is due to the way our amplifier it is connected to the DAQ board and to the Cryostat.  

 

 

*    GENERAL DESCRIPTION

 

 

      At the top of the screen you will find this button, the purpose of it is to STOP running the program. It takes a couple of seconds to stop the program, because the program finishes the calculations that it was doing and then stops.

 

            We are going to start describing the buttons that are found on the far left, from the top to the bottom.

 

            At the top left, there are 2 clocks, The left one displays the time in BERKELEY, CA. The right one displays the time of the last shot (Excitation).

 

  This button will allow you to change the parameters while it is off; when the red arrow is lit it is not possible to change the parameters (In the picture, it is off.)

 

 If you click on the folder, you will select the directory where you want to save your data or you can give a pre-assigned path on the slot below the folder.

 

 Below the previous button, there is a message dialog box where the program will display the calibration status of the program. It will also display if the data is being saved or not.

 

 

   When you press this button, the software tells the DAQ board to create a pulse with characteristics specified at the parameter panel. The creation of the pulse will also activate the features related to the excitation (quench and the preamp enable). How and when these features are activated is specified at the parameter panel.

If the program is in Auto mode, you do not have to press the SHOT button at any time. (We will explain later the Auto mode application)

NOTE: For this application to work, Lab View has to be in Run mode

 

This button turns on and off the Auto Save mode. When the arrow is not lit the Auto Save mode is off. (The picture says that Auto Save is ON)                       

Every time you push the SHOT button for the first time, if the Auto Save is on, the program will ask you where you want to save your data.  If this application is off, no data is going to be saved, however the program will create a file containing the time of the shot, the time in BERKELEY, CA since 1904 (Lab View features) and other data.

 

In case the Auto Save is off and you want to SAVE the data, there exists a button for that purpose. It is the following,

 

 This application works after you press the SHOT button and when the Auto Save mode is off. If you pressed SAVE for the first time, you will be prompted where you want to save the data. If you have already said where to save it using the Auto Save mode, you will not be asked again.

 

The next 5 buttons have the following characteristic in common. After you click any of them, another window running a different program will appear.  This new program will take control of the entire software. It will use the settings and parameters specified at The New NMR.vi (The main program) and unless you close the new window, you will NOT be able to modify them. NOTE: To use these applications The New NMR has to be in Run mode.

 

 This button will display the Korringa Temperature Measurement panel (KTM panel). For further information about it go to the corresponding section.

 

 This button will display the Tip angle panel (TP panel). Further information; go to the TP panel section.

 

 

 This button will display the Spin Echo panel (SP panel). Further information; go to SP panel section. Information about this panel is not available yet.

 

 

 This button will display the Tune panel. Further information; go to the Tune panel section. Information about this panel is not available yet.

 

 

 This button will display the Calibration panel. Information about this panel is not available yet.

 

  The thermometer is calibrated when the indicator is on. Currently, the indicator is not lit

 

 

 Information about this panel is not available yet.

 

 

 This button, when pressed, will enable the Auto mode. The purpose of this application is to create pulses equally spaced in time. The Parameters of the pulses will be the ones specified in the parameter panel. However, it is possible to change the parameters during the Auto mode application only if the Lock parameters button is NOT pressed.

NOTE 1: When you pressed this button, the program will wait the amount of time specified in the Delay between Points control (next item) to create the first pulse.

NOTE 2: The button works as a toggle button, when OFF the label says Start Auto Mode. When it is ON, it says Stop Auto Mode.

 

 

This control will display the time in seconds between pulses. In addition, the arrows allow changing the amount of time between pulses.

 

 

This indicator will display the time (in seconds) left for the next pulse to be created.

 

 

This button will lock the Auto Mode application only. When pressed, the Auto mode cannot be stopped and the amount of time between pulses cannot be modified.  It is on when the arrow is bright red. Currently, the control is off.

 

*    Description of the Parameter Panel

 

This is how the Parameter panel looks.

 

 

 

1.      The excitation box

 

Four controllers in this box allow you to change the parameters of the excitation pulse. This pulse will be one of the many generated by the DAQ board. As you can see from the box, it is possible to modify the amplitude of the pulse, the frequency, and the number of periods of the pulse. The Update rate will modify the number of points per second created by the DAQ board. NOTE: Those points form eventually the excitation pulse.

 

 

2.      The Quench box

 

The controllers in this box will modify the parameters of the quenching pulse. The labels of the controllers explain the function of each of them. For example, in the case illustrated in the box, the baseline of the quenching pulse (Low Value) will be - 4V. The quenching pulse will be created at the same time the excitation pulse is created (Delay after exc.). This pulse will Rise until some max voltage for 5.60 ms and then stop, it will Stay for 14.80 ms at that same voltage and then Fall for 50.00 ms. The pulse will Fall in different forms, as an Exponential, as a Sinusoidal or in a specified way by the user (Custom).  In the previous example, the Fall will be Sinusoidal.

 

3.      The Enable Preamp box

 

The controller in this box will allow the user to specify to the DAQ board when to create the Enable Preamp pulse. This pulse has the form of a Step function, which in our experiment has been used as a switch that connects part of a circuit. As the label of the controller explains, the time specified in the controller will be the delay after the quenching pulse gets to the max voltage. You can check from the example box that this time could be negative.

 

 

4.      The Acquisition box

 

The acquisition box specifies the Channel of the DAQ board that is reading the analog input, in the case of our experiment; this input is the NMR signal (FID). Now, the DAQ board digitizes the input, so with the Scan Rate control you will be able to indicate how often the DAQ board should read the analog input pulse. Then, the # of scans control will specify the number of points that you want the DAQ board to read from the analog pulse. The last control is called Limits, this control will modify the resolution of the “y” axis, which in our case (unless otherwise specified) will be voltage. To obtain the resolution you just have to divide the value at the Limits control by 212 (The 12 comes from the way the information is stored in the DAQ board). For example, if the value of the Limits control is 10.00 V, then the voltage resolution is approx. 2.5 mV. This means that it will not be possible for the DAQ board to read voltages that are less than 2.5 mV. This last feature has helped us to get ride of certain type of unwanted noise. Finally, the 500 kHz LP filter helps, when it is ON to reduce the amplitude of signals with frequencies bigger than 500 kHz. This indicator is ON when the light is bright green.

 

MAIN CHART

Figure 2, Main Chart

 

You can find the Main Chart just below the Parameter panel. This previous Voltage vs. Time chart will display 4 different graphs. The NMR signal (in orange), the Excitation pulse (in red), the Quench pulse (in blue), and the Preamp Enable pulse (in green). The features of this chart are the usual ones of Lab View generated charts.

 

There are two other graphs to the left of the Main chart. There is a small square, one, labeled FFT (see Figure 3), and a little bit more to the left there is the other one. This last Voltage vs. Time chart will display ONLY the NMR signal that was already displayed on the Main chart.

Figure 3, FFT Window

 

            This FFT window will display the Fast Fourier Transform (FFT) of the NMR signal. In order to obtain a FFT of the NMR signal you have to specify to the program some parameters. In order to do that, when the program is in Run mode, you have to press the FFT … button, located on top the chart in Figure 3. When you press this button, the Fourier Transform Settings panel (FTS panel) will pop up. For further information about this panel, go to the section FTS panel.

NOTE: Absence of the FFT graph, after having an NMR signal, may be due to the scale of the graph.

 

Figure 4, NMR Response

 

 

            Below the Main chart is the NMR response chart. There will be two different graphs here, one of the NMR thermometer and the other one that correspond to the LCMN thermometer. The graph that concerns the NMR, displays the integration of the FFT of the NMR signal after each excitation pulse. This means that if you are in Auto Mode you will obtain one point after each excitation pulse. There are two indicators below the legend of this chart; the first one will be the value of the integration.

NOTE:            The LCMN thermometer was not connected to the fridge while this manual was being written so the features for this part are unavailable. However, the Lab View program for this feature runs perfectly.

 

Fourier Transform Settings panel (FTS panel)

 

            This is how the FFS panel should look.

 

 

            This panel will pop up after you press the FFT button on the front panel. The FTS panel contains two charts, the upper one will display the NMR signal (FID) and the lower one will show the Fast Fourier Transform of the NMR signal.

As you can see from the upper chart, there are two blue lines over the NMR signal. These vertical lines will tell the program what part of the NMR signal has to be included in the Fourier Transform. In order to change these limits, there are 3 options. You can click and drag the line; you can click on the line and then change its position by clicking on the little figures inside the rhombic structure next to the chart.

You can also use the 4 slots in the Control box to specify numerically the limits. You can find the Control box above the rhombic figure, next to the chart. The way the slots are arranged is the following:

 

X1

Y1

X2

Y2

 

Where the sub index 1 is for the line that is on the left side of the chart and the sub index 2 is for the line to the right.

While you move the limits of the Fourier Transform on the NMR signal, you should be able to see how the lower graph adjusts to those new limits. The lower chart also has two vertical lines, this time brown ones. In this case, these lines will specify limits of integration that will allow you to obtain the area under the curve of the Fourier Transform. The way to change the limits of integration is the sane as in the case of the Fourier Transform.

There are a couple of features in this panel that are related to the way the Fourier transform is done. (Zero padding button and Window control) These will not be explained in this manual.

One of the other buttons was used to Load NMR signals that were obtained in the past and that had to be analyzed again. The other two buttons save the limits of both charts (Save parameters) and Load limits previously used. (Load parameters)

Korringa Temperature Measurement Program

 

If The New NMR.vi is in run mode and you click the Korringa … button, the following panel will appear.


Figure No. 2 Korringa Temperature Measurement panel.

 

NOTE: Recall that if you do not close the KTM panel you will not be able to operate the front panel (The New NMR.vi)

 

 While in Run Mode, You CLOSE the KTM panel pressing this button.

 

            The KTM program has been modified several times since the first version. Currently the The New NMR.vi uses the program “korringa temperature measurement 20020718.vi”. The last numbers in the file name are the creation date of the file (Jul/18/2002)

NOTE: The software of this program contains several versions of the KTM program. All of these different versions were useful for the Packard Group at some point.

            In order to make you understand better the way the KTM program works here is a brief outline of how it works:

1.      The program generates an excitation pulse with a specified no. of periods, voltage, etc. (You can specify the no. of periods in the Parameter panel or in the KTM panel)

2.      After some time, which we will call SPACING TIME, another excitation pulse will be generated. This pulse will be identical to the previous one. The program obtained the spacing based on some initial parameters. (See Specifying the Spacing and Delay times section)

3.      After both of the excitations, two NMR signal will be obtained, even though you are not going to see them at KTM panel. The KTM program will graph in its Main chart the value of the integral of the Fast Fourier Transform of both signals. (The settings of the Fourier Transform are set on the FTS panel) We will call these two signals  a POINT. So a POINT will look like this:

You should see that both of the values have the same X-coordinate. You are going to distinguish between signals because of the color code. However, the upper value is the FIRST NMR signal that corresponds to the FIRST excitation pulse. In the same way, the lower value is the SECOND NMR signal, produced by the SECOND excitation pulse.

4.      ONLY the value of the SECOND NMR signal will be graphed in the Exponential fit chart. This chart is below the Main chat to the left.

5.      After a larger time than the spacing time, another excitation pulse will be generated. We will call this time DELAY TIME, which is the time between the second and third excitation pulse.

6.      The program will repeat steps 1 through 5. It will wait for an amount of time equal to the SPACING TIME to generate another excitation pulse. Then, it will graph both of the values of the NMR signal in the Main chart; however, again, only the last NMR signal (which in this case is the fourth one) will be graphed in the Exponential fit chart. Therefore, you will see two POINTS in the Main Chart of the KTM panel. You should see something similar to the following diagram:

 

 

In this graph you can see, that the new upper value corresponds to the third NMR Signal, which corresponds to the third excitation pulse. In the same way, the new lower value is the response of the system to the fourth excitation pulse.

 

7.      This program will graph as many POINTS as the Number of POINTS control (in the KTM panel) indicates.

8.      After the last POINT, the program will make an exponential fit of all the points that are in the Exponential fit chart. It is very important that you understand that these values correspond only to the lower values of the Main chart. (The idea behind this step of the program is to find the so-called T1 of the system).

9.      Using the values obtained with the exponential fit, the inverse of the decay constant (1/T1) will be multiplied by the Korringa constant. The result will be graphed on the T1 Chart. This previous chart is below the Main chart on the right side.

10. The values that the program displays in the T1 Chart are the temperature of the system … If everything is working properly.

Description of the controls, indicators, etc.

 

This control will let you specify the number of POINTS in the Main chart.

 

The Main Chart looks like the following picture:

 

On the legend of this chart, you will find the label First shot; this corresponds to the values of the FIRST NMR signal, the upper values. The label Second shot corresponds to the SECOND NMR signal. Both values will make a POINT.

 

 This indicator show the time left (in seconds) for the next POINT.

 

This slot will tell you the location of the data that you are obtaining. The file will be saved as a TXT file.

Exponential Fit Chart

 

This chart will show the fit and the values of what we defined as the SECOND NMR signal, which are the lower values in the Main chart. The program will make an exponential fit after the last POINT is done. This fit is a straight line because the Y-axis is logarithmic. The Exponential fit chart is below the Main chart on the left side.

 

T1 Chart

 

           

This chart will display the temperature of the system, the indicator on the top right of the chart will show the last measure value of the temperature.

 

  This button will RUN the KTM program until the last POINT is done. (The number of POINTS is specified in the Number of POINTS control) 

 

 This feature will allow you to RUN the KTM program continuously. This means that every time the program finishes with the number of POINTS assign, it will start again.  For example, if you choose 4 POINTS and you press the Run Continuously button, the Main Chart will look like this:

 

            In this previous example, the first cycle finished and the second one is on the third POINT, after some time (the Delay time) the last POINT will be graphed.

            Every time a cycle is finished, the program will do the exponential fit and obtains a value for the temperatureT1, as explained at the outline.

 

Specifying the Spacing and Delay times

 

*      Spacing time

 

In order that the program knows what the Spacing Time is, the program needs to have a value of T1. The user has to give an initial value for the T1. (This usually means to give an approximate value of the temperature of the fridge, i.e. if you have an LCMN thermometer, you can make an educated guess) In addition, the user has to specify if the Y-scale is going to be Log or Linear (Time spacing control). In either case, the user also has to indicate the parameters in the respective controls. (Parameters for Log spacing control or Parameters for Linear spacing control) After some calculations, the program will obtain the Spacing time. At the same time, the KTM program will get another T1. (This happens ONLY if the system is running continuously. Refer to the KTM outline) In order to do that, this new value has to satisfy some criteria before it is used as a Spacing time. (T1 Fractional change limit control) The user sets this criterion. If it satisfies the criterion then the new T1 is used to obtain the Spacing Time, if not the initial value is used again.

 

  With this feature, you can choose the type of scale of the Y-axis of the main chart (The main chart is the one that display the NMR Response). There are two options: one is linear and the other is Log. This last one accounts for logarithmic, even though it is not the common logarithmic scale. The difference is that the logarithmic scale of this program is made so that the exponential fit gets more points at smaller times than at larger ones. The reason is that the decaying function will change a very small amount after a couple of decaying constants. Therefore, we thought that the fit would be better when there are more points in the region where the decaying function is changing a lot.

 

            We will call the previous control the T1 guess Control. This control is important because it will allow you to indicate the initial value of the T1 (in seconds).

            The next control will let you specify the maximum fractional change (∆T1/T1) that the T1 can have

 

           

            The following control is the Parameters for Log Spacing Control. This control will allow you to specify the parameters of the Log scale. The first control specifies the FIRST Spacing time; the second control indicates the increment of that Spacing Time.

NOTE: The resulting Spacing time after the first known spacing time is not just the sum of the previous spacing time plus the increment, i.e. it is not linear.

 

 

This next control is the Parameters for Linear Spacing Control. This control will be activated if the Time spacing control is set on Linear. This control works similarly to the previous one. The value of T1 and the value in the upper indicator on the control will set the Spacing Time. The lower indicator will be the increase, after some calculations, of the Spacing time.

 

 

 

 

 

 

 

*      Delay Time

 

            The following picture is the Delay time control. There are two controls in it, the one-labeled Delay and the Delay Nt1. In addition, there is a toggle switch on the top left corner. This switch will control the Auto delay mode.

 

As we explained before, the Delay time is the time between POINTS (following the convention used in this manual). The program has two different options for this feature. One of them is when the Delay time is constant and the other one is when it changes (Auto Delay mode). When the Auto delay mode is OFF, the Delay time will have to be set on the control labeled Delay. In this case, the time between POINTS will be the number (in seconds) in this control.

            When the Auto delay mode is ON the delay time has to be assigned in the Delay Nt1 control. In order to obtain the Delay time in this mode first, the user has to set the initial T1 guess (Using the T1 guess control). Then, the value set on the Delay Nt1 control will be multiplied by this previous T1 guess and the time between POINTS will be the result of that operation. However, if the KTM program is running with the Run continuosly button pressed, only the first cycle will use the initial T1 guess to calculate the Delay time. The next values of the Delay time will be calculated with the new T1’s obtained from the exponential fit of the lower POINTS (Refer to the Run continuosly button and the outline). In other words, if you are in Run continuously mode the Delay time will be changing every CYCLE.

 

Optional applications for the KTM Program

 

The following optional features will allow you to specify, for each measure of T1, the number of periods of the excitation pulse. This means that in one CYCLE the same number of periods will be used to measure the temperature of the system (or T1) but using the next controls you will be able to decide how many periods per cycle the excitation will have.

 

 This control will specify the number of periods of the first (that is why the control is labeled START) excitation pulse when you run the Korringa program.

NOTE: The value assigned to the no. of periods of the excitation pulse in this control will overwrite the number specified in the Parameter panel.

 

 This control is the Number of Periods Increment Control. It will specify how many periods the excitation pulse will increase every time it is created.

 

This control will indicate the maximum no. of periods the excitation pulse can have.

 

These three last controls are related in the sense that the first control assign the no. of periods for the first excitation pulse, the second control will say that the second pulse will have (using the values of the pictures) 1 period more than the first excitation pulse an so on.  Finally, the third control assigns the no. of periods that the last excitation pulse must have.

 

 This control will let you specify how many values of the “temperature” T1 will be obtained with the same number of periods of the excitation pulse. After the last excitation pulse assign in this control, the next excitation pulse will increase the number of periods by the number assigned in the Number of periods increment control.

 

 This indicator will tell you how many excitation pulses have already been created with the same number of periods. In other words, this number will show how many T1’s have been obtained with an excitation pulse, with the same number of periods.

 

 This button, when on, (The arrow in the button will be bright green when on) will save the NMR signals.

 

            This next control will modify the parameters of the LCMN thermometer. The information is not available yet.

 

 

 

 

Tip angle panel

 

            If the Main program is in Run mode and you press the Tip angle button, the following panel will pop up:

 

 

This previous button will close the Tip angle panel. Remember that it is not possible to modify or interact with the Main program if this application is NOT closed.

 

This program will allow you to observe and measure the behavior of the NMR response as a function of the number of periods. In other words, with this program it is possible to obtain a relation between the tipping angle of the magnetization and the NMR response. With the understanding that the NMR response is the integral of the Fourier transform of the actual NMR signal (FID).

The way this program works is the following:

            The Tip angle program creates an excitation pulse (with most of its parameters specified in the Parameter Panel) with an assign number of periods, and then it graphs the NMR response. After a later time, the program creates another excitation pulse with different number of periods and then again, it graphs the NMR response. This same process continues until the program satisfies a criterion.

Description of most of the controls, buttons, etc.

 

 

This previous control lets you specify the number of periods of the FIRST excitation pulse.

 

 

  

This control will let you specify how many periods the excitation pulse will increase each time it is created.

 

                                                   

 

 This will let you assign the amount of time (in seconds) the program will wait to create the next pulse. This time is fixed.

 

 

 

This previous control will set how many excitation pulses the program will generate. After this criterion is satisfied, the program will STOP.

 

 

 

 

After choosing the parameters of the excitation pulse (in the Parameter Panel of the Main Program), the user has to specify the parameters of the Tip angle. Then this program will be ready to go. If you Press the Go! Button the program will start running.

 

                       

The data obtained while running this program will be stored in the file specified in the slot that is shown in the previous picture.

 

The following chart will display the NMR Response as a function of the number of periods. The indicator at the top right will show the numerical value of the NMR response.