Channel Settings > Acquisition Method

Previous | Next

Acquisition Method

Note: Some products do not support this feature.

The Acquisition Method options allow you to select the method used for displaying data on your monitor and storing it to your hard drive. A description of each method is provided below.

All DATAQ Instruments hardware products continuously sample data using a burst sampling technique. With the burst sampling technique, the board or hardware device samples data at one rate (referred to as the maximum sampling rate or burst rate) while your computer reports (i.e., displays and stores) this data at another rate (called the sample rate or throughput rate). Again, the burst rate determines how fast the board or hardware device samples your data and the sample rate determines how fast the sampled data is reported. Your board or hardware device can sample data much faster than it can report it. For example, let’s say we want to record one channel of data at 100 Hz and our burst rate is set at 10 kHz. (burst rate is modifiable through the Maximum Sample Rate command on the Preferences (in the Edit menu) and Sample Rate is modifiable from the Edit menu). In this example, we are sampling the data at 10 kHz and reporting it at 100 Hz. This means that for every 100 data points sampled, only 1 will be reported. The dilemma becomes: which data point out of the 100 gets reported? Fortunately, you have a choice of methods for reporting this single data point by use of the radio buttons on the right-hand side of the channel settings dialog box.

Average

Default method. This method averages all of the data points in the burst sample and reports this average as the single value for storage and display.

Filter (DI-1120, DI-2108, DI-4108, and DI-4208)

Default method (replaces Average in other DATAQ devices). The DI-1120, DI-2108, DI-4108, and DI-4208 employ a low-pass filter per analog channel with automatic corner frequency selection. The filter is a CIC (cascaded integrator comb) type that uses as many as 512 samples per channel to calculate in real time as data is acquired. Filter response is optimized when sampling frequency is set to ten times the highest frequency of interest.

Average (DI-2108-P)

Default method. This method averages all of the data points in the burst sample and reports this average as the single value for storage and display.

Check the Unipolar checkbox for gain settings of 0-5 and 0-10V.

Last Point

This method reports the last input data point in the burst sample for storage and display. The rest of the data points in the burst sample are ignored.

Maximum

This method reports the highest value data point in the burst sample for storage and display. The rest of the data points in the burst sample are ignored.

Minimum

This method reports the lowest value data point in the burst sample for storage and display. The rest of the data points in the burst sample are ignored.

RMS

Converts AC signals to DC data. The square root of the mean square value, computed over the number of samples specified in RMS Window Size, is acquired and displayed for the selected channel.Note: You should specify the number of samples before selecting this acquisition method. To designate the number of samples and for a more detailed explanation of the RMS acquisition method see RMS Window Size.

Frequency

This method is for use with frequency measurements - allowing a more accurate representation of a frequency waveform by acquiring and displaying a value proportional to the frequency of the input pulses. The highest frequency that can be converted is half the device burst rate divided by the number of channels. Note: The Frequency preferences should be set before selecting this method. See Frequency for complete details.

Note: The RMS and Frequency Acquisition methods are not compatible with Triggered Mode or the checking Auto in Edit Preferences Maximum Sample Rate. These methods are implemented by software that changes the Filter acquisition method to Average for all enabled analog channels, degrading the sharp anti-aliasing rolloff of their frequency response.

Top