Arduino MKR Therm Shield for Precise and Extended Range Temperature Measurements

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Arduino team is on fire to build new extension boards and shields around their newly built popular MKR series board. Few weeks ago, we discussed about the MKR ENV shield which helps builder and DIY enthusiast to quickly prototype environment sensing projects on Arduino MKR. Today, we are going to talk about MKR Therm Shield which Arduino launched very recently for extended and precise range of temperature monitoring projects.

The MKR Therm Shield can be used with any MKR board family to acquire temperatures from a thermocouple of type K and a DS18Bxx digital one wire sensor. The Thermocouple is a kind of temperature sensor that offers high accuracy and a wide range of measured temperatures. Its analog nature requires specific interfacing and this shield relies on the MAX31855 thermocouple digital interface.

The two connectors of the MKR THERM Shield allow the usage of Type K thermocouples with or without a plug attached to the metal wires.

The MKR THERM Shield has its own library to read the temperature measured by the thermocouple. You may find further details and a usage example in our Getting Started page.specs of the ENV shield is given below –

Connectors K TYPE

DALLAS DS18S20  (to solder)

Screw terminal block

Input Voltage 3.3V
Operating Voltage 3.3V
Operating Temperature -200°C + 700°C
Communication SPI/1Wire
IC MAX31855
Length 61 mm
Width 25 mm
Weight 32 gr.

Thermocouples are based on the thermoelectric properties of a junction between two different metals and are capable of measuring with good precision ranges from -270 to +1372 Celsius (K type) that are far beyond any digital sensors or NTC/PTC (thermistor) range. A typical application of thermocouples is in boilers, soldering stations and coolers. Also good quality 3D printers rely on thermocouples to measure the extruder temperature.

The K thermocouple has usually two wires, made of Alumel and Chromel that need to be connected with special care: no solder, just mechanical connection, therefore we support on the shield both the standard K type connector and a screw terminal.

This particular sensor has the junction between the two metals that is the part that should be put where the temperature reading has to be made. If the junction for some reason breaks, it can’t be repaired. The tip of the thermocouple is where this junction is made, but there is also a second place where one metal is in contact with a different one: the connection with the K type plug or the screw terminal. Also in this junction between the two metals – one of the actual thermocouple alloy and one of the screw – the thermoelectric effect is present and some current is generated. That current is strictly related, as it should be, to the temperature of that junction.

The MAX chip we use on the shield takes all this in account and it returns the measured temperature at the tip (the junction) already compensated. For your reference, you can also read the temperature at the connector, value that is considered a reference.

MKR Therm

The great thing about all Arduino boards and shields is that, all are open source hardware, schematic and eagle files are available for download from Arduino official website.

 

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