Maxim > Design Support > Technical Documents > Subsystem Boards > APP 5683 Keywords: subsystem reference design, Industrial Automation, 4-20mA Loop Sensor SUBSYSTEM BOARD 5683 Monterey (MAXREFDES15 ): Ultra-Low Power, High-Accuracy 4 20mA 2-Wire Current-Loop Sensor Muhammad By: Qazi Carmelo Morello Oct 18, 2013 Abstract: The Monterey (MAXREFDES15 ) subsystem reference design is a high-accuracy industrial loop powered sensor transmitter that connects to any standard PT1000 resistance sensor and converts the linearized temperature to a 420mA current signal, which is immune to noise and remains constant over long distances. A similar version of this article appears on EDN, March 13, 2014. Introduction The 420mA current loop is widely used as an analog communication interface in industrial applications for transmitting the data from remote sensors to a programmable logic controller (PLC) in a central control center over a twisted pair cable. Here, 4mA represents the lowest temperature value, and 20mA represents the highest measured temperature. There are four main advantages of the current loop. First, the accuracy of the signal is not affected by the voltage drop in the loop, as long as the power- supply voltage is greater than the total voltage drop across the loop. Secondly, it uses two wires for power as well as data communication over the entire loop. Thirdly, it is more immune to More detailed image (JPG) noise. And lastly, it is offered at a low cost and easy installation. The Monterey design is based on a complete Maxim solution which combines ultra-low power, high accuracy, and high precision. 1. MAX44248 low-noise,. zero-drift op amplifier 2. MAX11200 high-accuracy, low-power, 24-bit delta-sigma ADC 3. MAXQ615 low-power microcontroller 4. MAX5216 low-noise, high-accuracy, low-power 16-bit DAC 5. MAX9620 low-power op amplifier 6. MAX15007, wide Input voltage low-power LDO This loop-powered sensor transmitter is targeted for industrial sensors, industrial automation, and process control, but it can be used in any application requiring high-accuracy conversion. Simplicity, reliability, good noise immunity, long distance, and low cost make the Monterey (MAXREFDES15 ) (Figure 1) interface well suited for industrial process control and automation of remote objects. Page 1 of 7 More detailed image (GIF) Figure 1. The Monterey subsystem design block diagram. Features Ultra-low power -100C to +100C interval High accuracy High precision Simple power supply and wide input range System current consumption less than 2.1mA Resistance temperature detector (RTD) PT1000 Resolution 10,000 counts or 0.1% Accuracy 0.25% Equipment Required 10V to 40V power supply High-accuracy current meter RTD PT1000 sensor or a temperature calibrator Quick Start Connect an industrial standard power supply across LOOP+ and LOOP- terminals of J1 to power up the board. Connect the sensor across J3. The current design of the board is configured for 2-wire RTD application. Minor modifications at the sensor side can be performed to use a 3/4-wire RTD application. Jumper Descriptions Table 1. Connector Description and Default Jumper Positions Jumper Default Position Function J1 Installed Power pin for Monterey Board. Connect across LOOP+ and LOOP- for power. J2 Installed J3 Installed Connect RTD across IN+ and IN-. Installed across pins Using a jumper across pins 1 and 2 of J4 uses the MAX44248. This case is used to gain the J4 1 and 2 input signal. Page 2 of 7