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Thermocouple output voltage isolation in temparature transmitter (4-20mA)

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Manu M S

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Hi...
I need to provide isolation for thermocouple for temparature transmission (4-20mA). Means i have to provide separate ground for thermocouple.. I selected analog devices ADum1100 digital isolator.
The only source is +24V which i am giving for XTR116 which outputs 4-20mA.
Problem is Isolation means i need to separate ground of thermocouple (-ve) from remaining grounds. If i use a digital isolator for isolation where +5V required for its operation is supplied by XTR116, isolation between thermocouple ground and other grounds wont happen? Please suggest me some ideas ....

If still information is required ask me i will post....


Thanks in advance...
 

The thermocouple is an analog device (not to be confused with Analog Devices), a DIGITAL isolator will do you absolutely no good. Also, you don't need to ground the thermocouple, you need to actually use a differential input device. There are LOTS of solutions, here's one: AD8494.
 

barry said:
The thermocouple is an analog device (not to be confused with Analog Devices), a DIGITAL isolator will do you absolutely no good. Also, you don't need to ground the thermocouple, you need to actually use a differential input device. There are LOTS of solutions, here's one: AD8494.
Click to expand...


Dear sir if i am using digital isolator i can interface this between my pic microcontroller (ADC) and DAC..

Direct thermocouple interface ICs are available but which are costly.....

Do AD8494 provides ground isolation? I studied its datasheet, they provide input filtering and amplification.. but not ground isolation...

or
Do common-mode rejection feature of ad8494 is same as ground isolation? i think not...
 

I don't understand. What are you isolating from what? Is the thermocouple grounded? What do you mean by "if i am using digital isolator i can interface this between my pic microcontroller (ADC) and DAC"? Your OP said nothing about a PIC. Where is the PIC in your signal chain? Do you want to isolate your PIC from ground?

Please clarify. A schematic or block diagram would help a lot.
 

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