Warthog Systems LabHelper X
          sampling rates
            using LabHelper

The SAMPLE RATE window offers a choice of button-selected sample rates.  You can also define your own sample rate by entering the desired rate (in seconds) in the edit field and then clicking the 'Use other interval' button.

Note that the standard rates are not always usable, depending on recording mode, A-D converter type, and the number of channels (the maximum sample rate drops as the number of channels increases). 

Note: with ADC-1s, relatively high input voltages (absolute value > .04 volts) are read slightly faster than lower voltages.  This is because the automatic gain function starts with the lowest gain, and then -- if necessary -- adjusts gain to achieve maximum resolution and makes a second reading.

It's possible to select any sample rate from the 'Use other interval' button.  If the selected rate is too fast for the number of channels used, the program shows a warning message.  If you ignore the warning, the program will try to keep up but may not be successful.  Data will be recorded and the computer will calculate the real sample rate (which may be slower than desired) and display it at the end of sampling (see below).

  •    If you are using an ADC-1 or DataTaker DT50/DT500, the maximum realistic sampling rate is about 3 to 4 samples/second, depending on the input voltage and machine type.  You can set the program to sample faster, but the internal voltage conversion of the converter will probably not keep up.  If you use an external A-D converter the SAMPLE RATE window will show all the higher sampling rates as activated -- but in reality an external converter can't sample that fast.   DT800s are considerably faster than DT50s or DT500s, but not as fast as a UI2.

  •   For Chart channels, you may adjust the desired duration of sampling using the buttons on the right side of the window.  Click one of the available present recording times, or increment the number of samples with the appropriate buttons ("<<" and ">>" decrease or increase the sample count by screenwidth samples; "<" and ">" increment by screenwidth/2 samples, and "max" sets the sample count to the maximum possible value.  In this example, the sampling rate is 10 samples/second, and by clicking on the "1 hr" key the total number of samples has been set to 36,000 to yield a total sample duration of 1 hour (3600 seconds).  Note that some preset recording times are not available because they would require more than the maximum possible samples, or they are too short for effective recording with the selected sample rate.  LabHelper X will not allow you to specify recording durations of less than 10 samples.

    For Oscilloscope channels, you can use a similar (but smaller) set of buttons below the trace duration box (in the lower left of the window).  You can set the recording time for the minimum possible (one screenwidth) to the maximum possible, in increments of 1 screenwidth.

  •   If you have set the alarm function (see the MENUS page for details), the maximum possible sampling rate decreases to some extent (particularly if large numbers of readings are averaged).  However, for most sampling rates, use of the alarm function has no negative effects.

  •   When data are gathered and subsequently saved, LabHelper X will keep track of the total number of samples and the starting and ending times, from which it calculates the average sample rate.  If the average rate differs more than a specified precision from the requested rate, the average rate is recorded in the data file.  This is displayed at the end of recording; see the options window page for details.  You can adjust the precision factor from the EDIT MENU.

  •    In Oscilloscope plus Chart mode, you are presented with the SAMPLE RATE window TWICE.  The first time is for selection of the Oscilloscope sampling rate.  The second time is for selection of the sampling rate for the Chart channels.  The title bar at the top of the window indicates which sampling rate is being selected.


    LabHelper X relies on software to keep track of time.  Unfortunately, it is possible to disrupt the timing functions.  To maintain a constant and consistent sampling rate, avoid 'distracting' the computer, particularly at high sampling rates.  'Distractions' include anything that causes OS X to temporarily switch attention from running LabHelper X to a different task.  Some hints:

    • Do not insert removable media (this will temporarily slow or halt acquisition while the computer mounts and verifies the new disk). 
    • Some storage media -- like some external hard drives -- go idle after a period of inactivity.  If the switch to idle occurs in the middle of a sampling episode, it's possible that sample timing will be disrupted.  To avoid this possibility, eject such disks before sampling begins. 
    • LabHelper X will run in the background, and at most sampling rates and averaging counts, data gathering can proceed with reasonable effectiveness.
                However, at high sampling rates, don't access other programs or items in the Apple menu.  This can slow acquisition to varying degrees.

    In general, it's a good idea to shut down other programs, including screen-savers, when LabHelper X is gathering data.

  • go to: