Issue measuiring differential voltage accurately.

Hi RedshiftBioEE 

Thank you for reaching out and sharing your inquiries with the team.

 Apologies for the late response, as we had a long holiday last week.

 Regarding your inquiry, I tried the AD8227 in Simulation with your design requirements for >1ksec, and the part is working fine. The output is within 2.49 for -10mV diff input.

 I would like to ask several questions regarding your application schematic and design requirements to better understand if there are any problems (if any).

1. What components and circuits are connected to TEC_CS+ and TEC_CS-?
2. The information being shared that the AD8227 was used for current sensing, is the current being forced or monitored constant throughout for a period of 1000 sec?

My next task: I’m trying to replicate your schematic and try to check in sims.

Regards,

Hi,

Thank you for looking into this. 

1. Connected to the inputs of the op amp is a .002 ohm shunt resistor tha is in series with a Thermoelectric cooler / H-Bridge driver. The tec typically runs up to +/- 12V, at 5A. (I think I must be hitting the max common mode voltage of the op amp, but I dont see this anywhere in the datasheet).

2. The amount of current isn't alway constant. In the 100- second graph, the current "turns on" at about 910s and turns off at about 990seconds. The current is constant for these 80 seconds while it is ramping down. 

Thanks.

Hello Aaron,

RedshiftBioEE said:

(I think I must be hitting the max common mode voltage of the op amp, but I dont see this anywhere in the datasheet

this online tool will help you to check the allowed signal ranges for your amplifier:

https://tools.analog.com/en/diamond/#difL=-0.01&difR=0.01&difSl=-0.01&gain=85&l=0&pr=AD8227&r=12&sl=12&tab=1&ty=1&vn=0&vp=12&vr=1.65

best regards

Achim