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OPA4188: OPA4188

Prodigy 90 points

Replies: 3

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Part Number: OPA4188

I try to build a thermocouple design. My aim is to detect the range of -200C to  +600 C. While I search convenient components to use in cold junction compensator and precision zero drift amplifier for output. Could you advise a design and components to achieve the range by details. 

  • Hello Kutluk,

    We have a TI Precision Design (TIPD120) that employs a common 3-wire Pt100 RTD. It is highly accurate, doesn't require cold junction compensation, and has a temperature range of -200 C to +850 C. You can view the information here:

    www.ti.com/.../slau520a.pdf

    Also, there is another TI Precision Design (TIPD209) specifically for a thermocouple that uses an RTD for cold junction compensation. Its useful temperature range is more limited, –50°C to +500°C. You can view the information here:

    http://www.ti.com/tool/tipd209

    Regards, Thomas
    Precision Amplifiers Applications Engineering
  • In reply to Thomas Kuehl:

    Dear Thomas, 

    Thank you for your answer. TIPD120 is convenient for thermocouple ? Can I connect directly ? If I do, how can I connect thermocouple to design ?  Or How can I enhance temperature range of TIPD209 from -200C to +600C?

    Have a nice day

  • In reply to Yildirim:

    Hello Kutluk,

    Since TIPD120 was developed around an RTD the circuit wouldn't be directly applicable to a thermocouple. The RTD has much lower output voltage change for a change in temperature than the thermocouple. Also, the RTD requires current excitiation to develop a measurable voltage while the thermocouple doesn't. It produces a voltage output in reponse to a temperature differential. 

    Certainly the TIPD120 amplifier and delta-sigma converter could be employed to convert the thermocouple voltage to a digital equivalent. However, because the thermocouple linearity isn't ideal some method must be employed to correct for nonlinearlty over temperature if accurate results are needed; especially below 0 °C. The type-K thermocouple provides about the best linearity across temperature of the various types available, but the cold non-linearity will likely be an issue.

    The TIPD209 design is optimized for the temperature range of -50 °C to 500 °C. I suspect this narrower temperature range was selected to capitalize on a more linear portion of thermocouple's temperature range, and to maximize the cold-junction compensation accuracy. If one is willing to tolerate the higher non-linearity across temperature, then the TIPD209 circuit could be modified for a wider temperature range. The instrumentation amplifier gain and reference voltage applied to the INA188 would need to adjusted to accommodate the voltage range produced by the thermocouple.

    Regards, Thomas

    Precision Amplifiers Applications Egineering

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