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TOPIC: A Thermocouple Measurement Circuit with Swordfish Software

Re: A Thermocouple Measurement Circuit with Swordfish Software 8 years 6 months ago #15436

  • Jon Chandler
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Thermocouples are popular temperature measurement sensors that cover a temperature range from well below zero °C to over a thousand °C.  They have good accuracy, are available in many configurations and are inexpensive.  This is not to say that they are easy to use!  Thermocouple are a measurement challenge:
  • Output levels are less than 50 mV and may be positive or negative
  • The “cold junction” temperature must be compensated
  • The output response is non-linear
Historically, measurement solutions to meet these challenges have been complex requiring several ICs  and many discrete components.  A few dedicated single chip solutions exist but all have shortcomings, including cost and availability.

I2C Single-Chip Solution

The TI TMP512/TMP513 Temperature and Power Supply System Monitor provides an ideal single-chip solution for thermocouple measurement.  The chip features a 12-bit ADC with an input range of 40 mV that can handle bi-polar signals, and an accurate on-chip temperature sensor for reference junction compensation.  Where maximum measurement accuracy is required, external PN temperature sensors may be used to measure temperature at the junction point.

 

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Re: A Thermocouple Measurement Circuit with Swordfish Softwa 8 years 6 months ago #6138

  • andyo
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Nice write-up and modules. The TMP513 looks like a good find. And I do like the "stay-where-I-put-you" Velcro board for prototyping!

Re: A Thermocouple Measurement Circuit with Swordfish Softwa 8 years 5 months ago #6398

  • Jon Chandler
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I just came across an article in Sensors Magazine using a similar approach using a Dallas-Maxim 1-Wire chip desired to monitor a lithium ion battery. Functionally, the chip is very similar to the TI TMP513 but it uses the 1-Wire bus instead of I2C. This is a nice option when you want to use several sensors spread over a wide area.

The 1-Wire Thermocouple, January 1, 2002 By: Dan Awtrey, Motorola Semiconductor

The DS2760 used in the article has been replaced by the DS2762.

It goes without saying that the Swordfish module for the TI TMP513 will not work with this circuit.

Re: A Thermocouple Measurement Circuit with Swordfish Softwa 8 years 5 months ago #6404

  • MrDEB
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I wonder if the module for the DS18B20 would work?
Being it uses the one wire protocol?

Re: A Thermocouple Measurement Circuit with Swordfish Softwa 8 years 5 months ago #6405

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Each 1+Wire device, just like I2C devices, has unique resisters which must be read and understood to calculate the measurement value. The 1-Wire protocol is the same for all 1-Wire devices, but the communication is unique to each device.

One other point to make in comparing these two solutions: The DS2762 is great for communicating over long distances compared to the short distances possible with an I2C interface. But you pay for this ability. The Maxim part is over $12 in small quantity, the TI part is less than $4.

Re: A Thermocouple Measurement Circuit with Swordfish Softwa 6 years 5 months ago #12901

  • Jon Chandler
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Dave Jones at EEVBlog has a nice video explaining how thermocouples work. Check it out for more information.

EEVBlog #419 - Thermocouple Tutorial
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