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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

By:

Muhammad

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 4–20mA 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 4–20mA 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

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.

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

Summary of content (7 pages)

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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 Qazi Carmelo Morello Oct 18, 2013 By: 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
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More detailed image (GIF) Figure 1. The Monterey subsystem design block diagram. Features Ultra-low power -100°C to +100°C 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.
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J5 Not installed J6 Not installed J7 Installed J8 Installed J9 Installed Using a jumper across pins 2 and 3 of J5 bypass the MAX44248. The input signal range is high and amplifier is not required. When not installed, this jumper’s subsequent pins can be used to measure the loopgenerated current.
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Transmitter The analog front-end combines the following: RTD sensor PT1000 Ultra-precision, low-noise, zero-drift operational amplifier (MAX44248) Ultra-low-power, high-accuracy delta-sigma ADC (MAX11200) The low-power microcontroller (MAXQ615) is used to implement calibration and linearization. The sensor used in the Monterey board is a platinum resistance thermometer (PT1000). The entire system offers excellent accuracy of wide temperature range from -100°C to +100°C.
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Santa Fe Board MAXREFDES5# AFE as receiver Munich USB2PMB1# adaptor board 1. Download the most recent version of the Munich USB2PMB1# board software, PMOD_SPI.ZIP. Save the software to a temporary folder and decompress the ZIP file. 2. Connect the USB cable between the Munich USB2PMB1# board and the PC; the USB driver is installed automatically. 3. Connect the Munich USB2PMB1# board’s 2 x 6-pin right-angle connector to the Santa Fe's 2 x 6-pin right-angle header. 4.
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Figure 4. Error change vs. temperature at 24V. Figure 5. Current limit vs. loop voltage with 1.6kΩ sense resistor. Figure 6. Current limit vs. temperature with 1.6kΩ sense resistor.
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All Design Files Download All Design Files Hardware Files Schematic Bill of materials (BOM) PCB layout PCB Gerber Firmware Files The Monterey reference design comes with firmware loaded on the system. For additional details, please contact the factory. Buy Reference Design Buy Direct: Monterey (MAXREFDES15#) Or Order the Monterey reference design (MAXREFDES15#) from your local Maxim representative.