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Table of Contents


Connecting to the 24/7 Data Acquisition Module


On-Board Reference

Digital Inputs

Analog Inputs

Programmable Gain

Input Protection

Allowable Input Impedance

Converter Noise and Effective Resolution

Other Sources of Noise and Offset Error

Tips For Measuring Small Voltages

Addressing the 24/7 WildCard Using Module Select Jumpers


Initializing the 24/7 Data Acquisition Wildcard

Specifying the Reference Voltage

Starting a Conversion

Calibration Options
Choosing the Sample Rate
Setting the Gain
Choosing Bipolar or Unipolar Conversion
Specifying 16- or 24-bit Resolution
Synchronizing Conversions
Specifying the Source Channels

Obtaining A Sample

Single- and Multi-Channel Sampling

Continuous Sampling from a Single Channel
Sequential Sampling from Several Channels

C Example Listing (pdf)

Forth Example Listing (pdf)


Appendix A:24/7 Data Acquisition Wildcard Pin-outs

Appendix B:24/7 Data Acquisition Wildcard Schematics (pdf)

24/7 Data Acquisition Wildcard Users Guide

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The sample period is equal to the multiplicative inverse of the sample frequency.

data acquisition board: sample frequencies

Table 5: Some representative sample frequencies.
You may set the integer n to any value from 19 to 4000.

Changing the sampling frequency as well as the gain impacts resolution. Table 6, taken from the manufacturers datasheet, shows the effect of the sampling frequency and gain on the effective resolution.

data acquisition board: effect of gain & frequency on resolution

* Values in parentheses indicate our own measurements of the effective resolution.
Table 6: Effect of Gain and Sample Frequency on Effective Resolution

In Table 6, the sample frequencies are rounded to the nearest whole number and values in parentheses indicate our own measurements of the effective resolution. The analog to digital converter internally adds approximately 1 μV of noise on its analog inputs. This limits the accuracy of the converter at different sample frequencies. The table shows that the other components on the module (including the analog switches and protection circuitry) add an additional 1 μV of noise to the analog to digital converter.

The 24/7 Data Acquisition Wildcard has a built in low pass filter that has a first notch filter frequency equal to the sample frequency and a -3dB frequency equal to about one quarter of the sample frequency (0.262 x sample frequency). At the sample frequency and integer multiples of the sample frequency, the filter attenuates input signals by more than 100 dB. For example, if 10 Hz is used as the sample frequency, there will be notches at 50 Hz and 60 Hz that will significantly attenuate all differential and common-mode noise.

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