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.

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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