How Can I Effectively Achieve a Sample Rate Less Than 5 Sa/sec on the DL850?
The lowest possible device setting for sample rate on the DL850 is 5 Sa/sec. There are however, different methods that will allow you to achieve much lower sample rates which includes the use of an external clock, decimation by the instrument, or decimation by our Xviewer software.
For instructions on how to perform the EXT CLK and Decimation methods on the DL750, please refer to the attached PDF.
External Clock Method:
Under the initial settings, the DL850 samples the waveform data using a clock signal produced by its internal time-base circuit. You can use an external clock (EXT CLK) signal to control sampling by applying the external clock signal to the EXT CLK IN terminal on the left panel of the DL850. One data sample is stored to the acquisition memory at every pulse in the EXT CLK signal. The DL850 can accept a maximum 9.5 MHZ EXT CLK signal.
Keep in mind that the EXT CLK is limited by the module specification, providing a higher rate EXT CLK cannot force the module to sample at a higher rate than its maximum sample rate. For example, the 701251 module max sample rate is 1 MSa/sec; any inputted EXT CLK above 1 MHz will be ignored by the module. You can use two equations to help calculate the custom Time/Div and Sample Rates.
Time/Div = Record_Length
Sample Rate = EXT_CLK
DL850 EXT CLK Setup Procedure:
1. Connect EXT CLK IN using a BNC Connector
2. Input a Square wave at desired frequency, TTL level (0-5Vpeak), and a minimum pulse width of 50ns
3. Press ACQUIRE to display the Acquire Menu
4. Select Record Length soft button and set the desired record length
5. Select Time Base EXT and make sure EXT is highlighted
Note: The DL850 does not display either the Sample Rate or Time/Div, but the record length will be displayed. When you control sampling using an external clock, you cannot change the time axis setting using the Time/Div knob. To change the time-axis display range, change the record length or zoom in on the time axis.
Decimation by Instrument Method:
Decimation is a technique used to reduce the number of samples. When saving data in ASCII format, data is decimated and converted to ASCII format before it is saved. In the DL850, decimation is called Data Removal Interval, and can be used to save a data point in specific intervals.
For example, a Data Removal Interval of “Per1000” means that for every 1000 points of data in your record length, 1 data point is converted to ASCII and saved.
DL850 Decimation (data removal interval) Setup Procedure:
1. Press FILE » Waveform(Save) soft button
2. Select Data Type » ASCII using the soft buttons
3. Press Waveform Save Setup soft button to display the Setup Menu
4. Navigate to the Interval category using the Jog Shuttle or Arrow Keys
5. Press SET and choose the desired interval
6. Confirm all Waveform Save Setup configurations
7. Press ESC » Execute Save to save ASCII data file
Decimation by Xviewer:
Xviewer Decimation (data removal interval) Setup Procedure:
1. Transfer or open the appropriate *.WVF, *.WDF, or *.CSV file in Xviewer
2. Click on File » Save As » More Options located at the bottom right corner of the Save As menu
3. Click on the Compression drop-down menu and select Decim
4. Click on the Compression Rate drop-down menu and select the desired interval
5. Confirm all save configuration and save destination
6. Click on Save to save the file