The MAXREFDES42 is a high-accuracy IO-Link® resistance temperature detector (RTD) temperature sensor reference design for use with a 2-wire, 3-wire, or 4-wire PT100 RTD over a wide temperature range. Built in an industrial form factor, the design makes use of Maxim Integrated’s highly integrated MAX31865 RTD-to-digital converter. A rugged, on-board female M12 connector allows off-the-shelf RTDs to be connected to the board using a standard M12 extension cable. The temp sensor performs accurate temperature conversions to 15-bit resolution with multiple fault detection features. A display shows coarse temperatures rounded to the nearest °C, while the IO-Link communication tracks and provides fine temperature values. This sensor utilizes IQ2 Development’s IO-Link device stack to communicate to any IO-Link version 1.1-compliant master. By utilizing an industrial DC-DC step-down converter, this reference design consumes minimal power. The board also contains a male M12 connector for connection to a compliant IO-Link master using a standard M12 cable. Connecting the MAXREFDES42# to a USB IO-link master such as the IQ2 Development iqInterface® IO-Link master, using their iqTool® software, allows for evaluation with a PC.
Refer to the Details tab for more information and lab measurement data. Design files and firmware can be downloaded from the Design Resources tab.
Features & Benefits
Features
IEC 61131-9
IQ2 IO-Link iqStack® device
IO-Link version 1.1 compliant
Nonvolatile memory for calibration
Fault monitoring
LED display for quick bring up (coarse temp values)
Resistance temperature detectors (RTDs) are resistors that increase resistance when temperature increases. Accuracy, stability, and repeatability over a wide temperature range make RTDs excellent in a multitude of industrial applications. RTDs are made of many materials and often they are made of platinum to avoid corrosion and oxidation. The PT100 is one of the most popular RTDs where the resistance is approximately 100Ω at 0°C, hence the name PT100.
IO-Link is the first open, field bus agnostic, low-cost, point-to-point serial communication protocol, used for communicating with sensors and actuators, that has been adopted as an international standard (IEC 61131-9).1 IO-Link finally standardizes interoperability of industrial equipment from all over the world. IO-Link can directly function from the PLC or can be converted from all standard field busses to IO-Link through a gateway, quickly making it the defacto standard for universally communicating with smart sensors like the MAXREFDES42#.
Maxim Integrated and IQ2 Development collaborated in designing the MAXREFDES42# as an IO-Link version 1.1-compliant IO-Link RTD temperature sensor reference design. The MAXREFDES42# design consists of an industry-standard Maxim Integrated IO-Link device transceiver (MAX14821), an efficient high-voltage step-down converter (MAX15062B), a Renesas® ultra-low-power 16-bit microcontroller (RL78) utilizing IQ2 Development’s IO-Link device stack, and a highly integrated RTD-to-digital converter (MAX31865). Figure 1 shows the system block diagram.
The MAXREFDES42 IO-Link RTD temp sensor consists of 4 main blocks: IO-Link transceiver, step-down converter, RTD-to-digital converter, and microcontroller as shown in Figure 1.
The MAX14821 IO-Link device transceiver is IO-Link version 1.1/1.0 physical layer compliant with configurable outputs (push-pull, pnp, or npn), reverse-polarity/short-circuit protection, and extensive fault monitoring, all in a tiny 2.5mm x 2.5mm WLP package.
The MAX15062B is a high-voltage, synchronous step-down converter that efficiently converts 24V to 5V in a tiny 2mm x 2mm, 8-pin TDFN package. The PWM operation maintains a constant frequency during all operating loads. The MAX15062 comes in many versions. The MAXREFDES42# temperature sensor uses the MAX15062B, which is preset for a 5V output.
The MAX31865 is an RTD-to-digital converter optimized for platinum RTDs. An external 400Ω 0.1% reference resistor (R13) with a typical temperature coefficient of 0.2ppm/°C sets the sensitivity for a PT100 RTD. If a PT1000 RTD is preferred, use a precision external 4kΩ resistor instead. The reference resistor value is also stored as an IO-Link parameter in the sensor and needs to match the corresponding reference resistor used. The highly integrated RTD-to-digital converter is available in a 20-pin TQFN package.
An ultra-low-power RL78/G1A microcontroller with current consumption down to 66µA/MHz provides system control. It features 64KB on-chip programmable flash memory, 4KB on-chip data flash, and operates down to 1.8V, all in a tiny 3mm x 3mm LGA package.
For protection, the MAXREFDES42# features transient voltage suppressor (TVS) diodes at the IO-Link interface. Transient voltage suppressor (TVS) diodes are not all equal. The SDC36 TVS diodes have a clamping voltage less than 55V and meet both IEC 61000-4-2 (ESD) and IEC 61000-4-4 (EFT). There are many smaller TVS diodes on the market that cannot meet these specifications.
The on-board female M12 connector allows off-the-shelf RTDs, such as an Omega PR-26E-3-100-A-M6-0150-M12-2 or PR-26A-3-100-A-M6-0150-M12-2, to connect to the board using a standard M12 extension cable as shown in Figure 2a. The reference design ships uncalibrated and comes with a 2-wire PT100 RTD located in the gray terminal block TB1. Important: If you connect an external RTD via the extension cable to the female M12 connector, you must remove the 2-wire RTD inside the gray terminal block TB1. The board also contains a male M12 connector for easy connection to a compliant IO-Link master using a standard M12 cable. The MAXREFDES42# typically consumes 11mA at 25°C.
Figure 2a. The MAXREFDES42 reference design with Omega 4-wire RTD and extension cable.
Description of Software
The MAXREFDES42 was verified using IQ2 Development’s iqTool software version 1.1.0.4, which comes with the purchase of the iqInterface IO-Link master hardware. IQ2 Development’s latest source code and documentation are available at the links below.
To get going quickly, go to the Quick Start section below for step-by-step instructions on how to find the appropriate Quick Start Guide. Figure 3 shows a screenshot of the IQ2 Development IO-Link iqTool software.
Figure 2b. The MAXREFDES42# reference design connected to an IQ2 Development iqInterface IO-Link master.
Figure 3. IQ2 Development’s iqTool software version 1.1.0.4.
Detailed Description of Firmware
The MAXREFDES42 ships preprogrammed as a working IO-Link temperature sensor ready to connect to an IO-Link master. The firmware targets a Renesas RL78 microcontroller and follows the simple flowchart shown in Figure 4. The firmware is written in C using the IAR embedded workbench from IAR Systems and utilizes IQ2 Development’s IO-Link device stack.
Figure 4. The MAXREFDES42 firmware flowchart.
After hot plug-in, the MAXREFDES42 waits for a wake-up signal from the IO-Link master. After receiving the wake-up signal, the MAXREFDES42 synchronizes to the IO-Link master’s 230.4kbps baud rate (COM3). Communication parameters are exchanged. The MAXREFDES42 then starts a cyclic data exchange every 3ms by sending the sensor process data to the IO-Link master. If the sensor is removed, the IO-Link master will detect a missing sensor.
Detailed Description of Use Cases
There are two different use cases that should be considered before purchasing the MAXREFDES42. Use case #1 simply includes the MAXREFDES42 with a user-supplied IO-Link master and an IO-Link cable as shown in Figure 5. The system is preprogrammed to operate in this configuration. Use case #2 is where the entire firmware development system is needed as shown in Figure 6.
Figure 5. Use case #1 is the MAXREFDES42# quick start system.
Table 1. Recommended Components Needed for Use Case #1
Use Case #1 (MAXREFDES42 Quick Start System)
Company
Description
Orderable Part Number
Maxim Integrated
IO-Link RTD temp sensor (ships programmed)
MAXREFDES42#
IQ2 Development
iqInterface IO-Link master
IOL1-B-DMU-W-CP001
Balluff
IO-Link cable (4-wire/2m)
BCC05MC
Figure 6. Use case #2 is the MAXREFDES42# firmware development system.
Table 2. Recommended Components Needed for Use Case #2
Use Case #2 (MAXREFDES42 Firmware Development System)
IQ2 Development’s iqTool (tested with version 1.1.0.4 and comes with IO-Link master)
M12 4-pin IO-Link cable (BCC05MC)
Note: Verify with IQ2 Development that your version of Windows is supported before purchasing their software.
Download, read, and carefully follow each step in the MAXREFDES42# Quick Start Guide.
Lab Measurements
Equipment Used:
Windows 7 PC with USB port
MAXREFDES42# board
IQ2 Development iqInterface IO-Link master
IQ2 Development’s iqTool (tested with version 1.1.0.4 and comes with IO-Link master)
M12 4-pin IO-Link cable
RD42_RL78_V01_00.ZIP ; where XX_XX = latest version from webpage
Fluke 7341 calibration bath
Omega HH41 thermometer
ETI Therma 1 thermometer
Fluke 189 multimeter
The lab measurements were taken using the setup and equipment shown in Figure 7.
Figure 7. Setup and equipment used for lab measurements.
Figure 8 shows error versus temperature referenced to the Omega HH41 thermometer and the ETI Therma 1 thermometer, respectively. The MAXREFDES42# connected RTD probe was placed in the Fluke 7341 and calibrated at 25°C. Click on the link below to see the NIST traceable certificate of calibration for the Omega HH41 thermometer used as a reference.
Figure 9 shows the MAXREFDES42# temp sensor’s 24V supply current versus temperature, demonstrating stable, low-current consumption.
Figure 8. MAXREFDES42# Error vs Temperature, using a PR-26A-3-100-A-M6-0150-M12-2, 4-wire RTD calibrated at 25°C.
The red data used the Omega HH41 thermometer as a reference. The green data used the ETI Therma 1 thermometer as a reference.
Figure 9. MAXREFDES42# 24V Supply Current vs. Temperature.
References
IO-Link System Description 2013 by IO-Link Company Community. Page 3, Preface.
IO-Link is a registered trademark of ifm electronic GmbH.
iqInterface, iqStack, iqTool are registered trademarks of IQ2 Development GmbH.
Renesas is a registered trademark and registered service mark of Renesas Electronics Corp.
Windows is a registered trademark and registered service mark of Microsoft Corp.
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