EVAL-CN0336-PMDZ: 300 kSPS PMOD Data Acquisition System

The system processes 4 mA to 20 mA input signals using a single 3.3 V supply. The total error after room temperature calibration is ±0.06% FSR over a ±10°C temperature change, making it ideal for a wide variety of industrial measurements.

The small footprint of the circuit makes this combination an industry-leading solution for 4 mA to 20 mA data acquisition systems where the accuracy, speed, cost, and size play a critical role. Both data and power are isolated, thereby making the circuit robust to high voltages and also ground-loop interference often encountered in harsh industrial environments.

The circuit consists of an input current-to-voltage converter, a level shifting circuit, an ADC stage, and an output isolation stage. The 4 mA to 20 mA input signal is converted to a voltage by resistor R3. For R3 = 120Ω and an input current of 4 mA to 20 mA, the input voltage to the level shifting circuit is: 0.48 V to 2.4 V. The diode D1 is used for protection against an accidental reverse connection of the input current source.

The voltage across R3 is level shifted and attenuated by the U1A op amp that is one-half of the dual AD8606. The output of the op amp is 0.1 V to 2.4 V which matches the input range of the ADC (0 V to 2.5 V) with 100 mV headroom to maintain linearity. The buffered voltage reference (VREF = 2.5 V) from the AD7091R ADC is used to generate the required offset. Resistor values can be modified to accommodate other popular input ranges as described later in this circuit note.

* This board is designed to interface through the EVAL-ADICUP360 which is an Arduino and PMOD compatible form factor development board. The board uses an open source Eclipse based Interactive Development Environment (IDE) which can be downloaded free of charge. The platform contains many hardware and software example projects, to make it easier for customers to prototype/create systems and solutions using the complete ecosystem provided.

The EVAL-ADICUP360 uses the ADuCM360 Arm Cortex-M3 processor as the main device on board. It has integrated dual 24-bit sigma delta converters on chip, which make it extremely flexible for both analog and digital application.