1 Introduction

This analog input module front-end design features 8 channels with each channel that can be configured to measure bipolar, universal voltage, and current inputs with a resolution of 16 bits. The module supports a scan rate of 1 ms for all 8 channels. Multiple input voltage ranges are supported with a programmable gain amplifier (PGA). Input ranges supporting up to 20% overrange. Any common-mode voltage (V_CM) is effectively rejected. An open-wire detection feature identifies a broken connection to the sensor field transmitter. The design supports the extended industrial operating temperature range of –40°C to 125°C. Table 1-1 summarizes the key parameters of this design.

All terminals are fully protected against overcurrent up to ±30 mA and overvoltage up to ±33 VDC (permanent). Surges according to IEC61000-4-5 (±1 kV at 42 Ω) are effectively suppressed. Measurements on this reference design board demonstrate 16 bits of effective resolution (or ENOB) and 13–14 noise-free bits (NFB), depending on the selected voltage input range. The accuracy at room temperature is < 0.1%. Table 1-2 summarizes the performance specifications for this design.