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Table of Contents

Introduction

Connecting to the 24/7 Data Acquisition Module

Hardware

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

Software

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)

Glossary

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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Digital Inputs

The 24/7 Data Acquisition Module has three TTL compatible CMOS digital inputs DIN-1 (pin 5), DIN-2 (pin 6), and DIN-3 (pin 3) on the Field Bus header (H2). You can read the digital inputs by calling Read_Digital_IO.

Analog Inputs

The 24/7 Data Acquisition Module features four true differential, or seven pseudo-differential, overvoltage-protected, high-impedance analog input channels. "Pseudo Differential" operation indicates that multiple channels share the same signal return, FIELD7 (pin 10 of H2). The 10 different input options are outlined in Table 1. The analog inputs are protected from electrostatic discharges of up to ±2000 volts and continuous voltages of up to ±70 volts by the resistors and analog switches in series with the analog inputs of the analog to digital converter. You can connect your transducer signals to the Field Bus (H2 on the 24/7 Data Acquisition Module) either through a ribbon cable or a screw terminal expansion board that breaks out the signals to screw terminal blocks. Shield the connecting wires for optimal performance.

data acquisition board: analog input connection options

Table 1: Analog Input Connection Options

Programmable Gain

The gain range of each channel is 1 to 128 allowing the input full scale range to be user-selectable from 0-20 mV to 0-2.5V for unipolar signals, or a genuine bipolar range of ± 20 mV, or a quasi-bipolar range of ±2.5 V. In all cases, the common mode range of the inputs is nominally 0-5V (precisely -30 mV to +5.03 V). If the input buffer is activated, the common mode range of the inputs is reduced, becoming +50 mV to +3.5V.

Input Protection

In order to protect the AD7714 chip, which otherwise could be easily damaged by excessive input voltages, the 24/7 WildCard includes input protection circuitry. Protection resistors of 2.2K ohms are placed in series with each analog and reference input, and analog switches isolate the AD7714 inputs. In addition to providing additional input channels, the analog switches in conjunction with a zener protection circuit prevent over and under voltages from reaching the AD7714. The inputs are protected to 70V continuously and up to ±2000V electrostatic discharges.

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