I learned a lot in the past few weeks regarding basic circuit design but still have some problems understanding the following simple issue:
How do I provide a return current path for my instrumentation amplifier circuit?
I have passive sensors (pyranometers that consist of thermopiles and measure sun irradiation, sensor specs are attached at the bottom of this post) that output a low voltage signal so I need to amplify it using an instrumentation amplifier.
The output of the sensor (depending on the current irradiation) changes very very slowly.
My passive sensor has only two wires, one named HI and one named LO. I'm attaching the sensor differentially to the instrumentation amplifier.
I have chosen the instrumentation amplifier AD8237 for this task: Datasheet
The datasheet of this In-Amp says:
"When the source, such as a thermocouple, cannot provide a return current path, create one, as shown in the following figure."
This is how I currently plan to hook up the sensor to my instrumentation amplifier:
Question:
From what I have read so far I need to provide a return current path in my case. Can I just do it like shown in the circuit above (using the 10M Ohm resistors)?
I'm concerned about the impedance here as my sensors have very low impedance (10-100 Ohm, as you can see in the specs below) and the INA-Inputs are high impedance (100 MOhm as you can see in the datasheet posted above).
Will I get problems here if I use the 10 MOhm resistors on the INA-Inputs?
Would I need to add series resistors in order to increase the impedance here?
(because the current will return through the path of least impedance so do I need series resistance here in order to prevent that)?
Or am I mistaken?
How would you create the return path in this case?
Sensor specs:
Thank you very much for your help!
How do I provide a return current path for my instrumentation amplifier circuit?
I have passive sensors (pyranometers that consist of thermopiles and measure sun irradiation, sensor specs are attached at the bottom of this post) that output a low voltage signal so I need to amplify it using an instrumentation amplifier.
The output of the sensor (depending on the current irradiation) changes very very slowly.
My passive sensor has only two wires, one named HI and one named LO. I'm attaching the sensor differentially to the instrumentation amplifier.
I have chosen the instrumentation amplifier AD8237 for this task: Datasheet
The datasheet of this In-Amp says:
"When the source, such as a thermocouple, cannot provide a return current path, create one, as shown in the following figure."
This is how I currently plan to hook up the sensor to my instrumentation amplifier:
Question:
From what I have read so far I need to provide a return current path in my case. Can I just do it like shown in the circuit above (using the 10M Ohm resistors)?
I'm concerned about the impedance here as my sensors have very low impedance (10-100 Ohm, as you can see in the specs below) and the INA-Inputs are high impedance (100 MOhm as you can see in the datasheet posted above).
Will I get problems here if I use the 10 MOhm resistors on the INA-Inputs?
Would I need to add series resistors in order to increase the impedance here?
(because the current will return through the path of least impedance so do I need series resistance here in order to prevent that)?
Or am I mistaken?
How would you create the return path in this case?
Sensor specs:
Thank you very much for your help!