MONTEREY (MAXREFDES15#): Ultra-low power, high accuracy, 4–20mA, 2-wire current loop sensor

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4–20mA current loops are widely used as analog communication interfaces in industrial applications to send data from remote sensors over twisted pair cables to a programmable logic controller (PLC) in a central control center . In the design, 4mA represents the lowest temperature value, and 20mA represents the highest measurement temperature. The main advantages of the current loop are fourfold: first, the signal accuracy is not affected by the voltage drop in the loop, as long as the supply voltage is higher than the total voltage drop of the loop; second, using two wires as the power supply and the entire Loop data communication; third, better noise immunity; finally, low cost and simple installation.

The Monterey design is based on a complete Maxim solution and combines ultra-low power consumption with high accuracy and precision.

1. MAX44248 low-noise, zero-drift op amp

2. MAX11200 High-Accuracy, Low-Power, 24-Bit Delta-Sigma  ADC

3. MAXQ615 low-power microcontroller

4. MAX5216 low-noise, high-precision, low-power 16-bit DAC

5. MAX9620 low-power operational amplifier

6. MAX15007 wide input voltage range, low power LDO

Loop-powered sensor transmitters are targeted at industrial sensors, industrial automation, and process control, but can be used in any application that requires high-precision conversion.

Simplicity, reliability, good noise immunity, long range, and low cost make the Monterey (MAXREFDES15#) ( Figure 1 ) interface ideal for industrial process control and remote object automation.

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Figure 1. Monterey subsystem design block diagram

characteristic

• Ultra low power consumption

• -100°C to +100°C range

• High accuracy

• High precision

• Simple power supply and wide input range

• System current consumption is less than 2.1mA

• Resistance Temperature Detector (RTD) PT1000

• Resolution is 10,000 words or 0.1%

• Accuracy is 0.25%

Equipment required

• 10V to 40V power supply

• High precision ammeter

• RTD PT1000 sensor or temperature calibrator

Quick start

• C connect the industry standard power supply to the LOOP+ and LOOP- ends of J1 to power the circuit board.

• Connect the sensor to J3. The current design configuration of the board is for a 2-wire RTD application. With minor modifications to the sensor side, it can be used in 3/4-wire RTD applications.