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Analog Temperature Sensors - AD8494/AD8495/AD8496/AD8497

Product Number: AD8494/AD8495/AD8496/AD8497
Software Version: not applicable

Hi,

I would like your help to clarify some topics about the mentioned thermocouple amplifiers. (AD8494/AD8495/AD8496/AD8497)


 - The datasheet for those parts describe a 5 mV/°C output considering a 5V single supply. How does this value changes with the input supply voltage?  i.e., when a 3V single supply is used does the sensitivity changes to 3mV/C?


 - The ambient temperature (Reference junction) follows 2 typical ranges (0C to 50C and 25C to 100C) for the specified performance. Does it mean that this sensor in not suitable for applications when that reference junction ( or acquisition board) operates in temperatures below 0C (even if is stated that the device operate from -40C to 125C?


Thank you for your attention,

Best regards,

Fabio    

Top Replies

    •  Analog Employees 
    •  Super User 
    +1 verified

    Hi  ,

    Thank you for reaching out. To further understand the problem and be able to formulate the correct recommendations, we would like to know more about your applications and design parameters.

    Here…

Parents
  • Hi  ,

    Thank you for reaching out. To further understand the problem and be able to formulate the correct recommendations, we would like to know more about your applications and design parameters.

    Here are several items for your confirmation:

    • What application is the part being used? Example: Is this to measure a temperature inside an oven, instrument, etc..  and where is our ADI part located (based on the first example, is this inside the oven or outside)?
    • What temperature value is being measured? And can you validate the temperature in the reference Junction ( this is the area in the PCB where the thermocouples wires are connected)
    • Need to confirm your preferences; J or K-type thermocouple?
    • What are your desired values of the supplies? +Vs (Pin7), -Vs (pin3), REF (pin2)

    Regarding your questions, here are my responses below:

    1. The datasheet for those parts describes a 5 mV/°C output considering a 5V single supply. How does this value changes with the input supply voltage? i.e., when a 3V single supply is used does the sensitivity changes to 3mV/C?

                  ArSol: This is the transfer function that is guaranteed by the Datasheet for both Single and Dual Supply configurations.  This value doesn’t change upon varying the supply values and CJC was designed to generate a 5 mV/°C output transfer function.

    1. The ambient temperature (Reference junction) follows 2 typical ranges (0C to 50C and 25C to 100C) for the specified performance. Does it mean that this sensor in not suitable for applications when that reference junction ( or acquisition board) operates in temperatures below 0C (even if is stated that the device operate from -40C to 125C?

                  ArSol: The part is still functional and useable when the reference junction is in subzero temps; but it will not guarantee a +/- 2°C  Error when the application ambient temp is outside of this range. This simply means the error might possibly increase beyond +/- 2°C.

                  Note: If the TC Inamp part(AD849x) is being housed inside a machine, and there are several factors to take into; the heat from the PCB and other discrete parts. This will further elevate the interior temp and possibly rise to >25°C. Hence, it can suffice to reference junction temp requirement.

    Hope this information helps you.

    Regards

Reply
  • Hi  ,

    Thank you for reaching out. To further understand the problem and be able to formulate the correct recommendations, we would like to know more about your applications and design parameters.

    Here are several items for your confirmation:

    • What application is the part being used? Example: Is this to measure a temperature inside an oven, instrument, etc..  and where is our ADI part located (based on the first example, is this inside the oven or outside)?
    • What temperature value is being measured? And can you validate the temperature in the reference Junction ( this is the area in the PCB where the thermocouples wires are connected)
    • Need to confirm your preferences; J or K-type thermocouple?
    • What are your desired values of the supplies? +Vs (Pin7), -Vs (pin3), REF (pin2)

    Regarding your questions, here are my responses below:

    1. The datasheet for those parts describes a 5 mV/°C output considering a 5V single supply. How does this value changes with the input supply voltage? i.e., when a 3V single supply is used does the sensitivity changes to 3mV/C?

                  ArSol: This is the transfer function that is guaranteed by the Datasheet for both Single and Dual Supply configurations.  This value doesn’t change upon varying the supply values and CJC was designed to generate a 5 mV/°C output transfer function.

    1. The ambient temperature (Reference junction) follows 2 typical ranges (0C to 50C and 25C to 100C) for the specified performance. Does it mean that this sensor in not suitable for applications when that reference junction ( or acquisition board) operates in temperatures below 0C (even if is stated that the device operate from -40C to 125C?

                  ArSol: The part is still functional and useable when the reference junction is in subzero temps; but it will not guarantee a +/- 2°C  Error when the application ambient temp is outside of this range. This simply means the error might possibly increase beyond +/- 2°C.

                  Note: If the TC Inamp part(AD849x) is being housed inside a machine, and there are several factors to take into; the heat from the PCB and other discrete parts. This will further elevate the interior temp and possibly rise to >25°C. Hence, it can suffice to reference junction temp requirement.

    Hope this information helps you.

    Regards

Children
  • Hi Arsol,

    Thank you for your prompt reply.

    • What application is the part being used?

    For the thermocouple, a range from -30 to 400 C is fine.

    • Example: Is this to measure a temperature inside an oven, instrument, etc..  and where is our ADI part located (based on the first example, is this inside the oven or outside)?

    However, the ADI part will be located in a environment where the temperature should change between -30C and +45C.

    • What temperature value is being measured? And can you validate the temperature in the reference Junction ( this is the area in the PCB where the thermocouples wires are connected)

    It was expected the ADI part to do the compensation for the reference/cold junction internally. But adding a temperature sensor closer to the that point is also possible. 

    • Need to confirm your preferences; J or K-type thermocouple?

    K-type thermocouple should be the preferable one.

    • What are your desired values of the supplies? +Vs (Pin7), -Vs (pin3), REF (pin2)

    Single supply +Vs = 2.7V and a reference point with some offset to allow the measurement of a negative temperatures.

    Thank you for your attention.

    Regards