AD8628 PDF

V Input offset drift: 0. Operation is fully specified from 2. No external capacitor is required. V, drift of less than 0. Position and pressure sensors, medical equipment, and strain gage amplifiers benefit greatly from nearly zero drift over their operating temperature range. C Information furnished by Analog Devices is believed to be accurate and reliable.

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This amplifier was recommended by Dexter Research, a thermopile manufacturer. One thermopile is equipped with broad-band optical window which admits a lot of light, and the others have narrow-band windows.

Our stronger signals are showing oscillating behavior with a long time constant, around 2 seconds. I set up an experiment in which I exposed our sensor to ambient conditions, then placed it in front of a blackbody radiator, and finally returned it to its original position.

This is what I consider a good result. It comes from one of our weak, narrow-band detectors. The gain is very high, X in a single stage, but it appears to be clean.

The horizontal time scale in all graphs is 2. Our broadband detector admits more light. The gain is X but the raw signal is stronger. When I repeated the experiment above, I obtained this. Notice the strong peaks on the leading edge of the pulse, and the long settling times on both the rising and falling edge.

I was concerned that my movement of the sensor was not very exact, so I repeated the experiment with the sensor fixed in place. I blocked the black body with an insulating Styrofoam sheet, and raised and lowered the sheet to record the response and the recovery. This setup improved the large-signal response, but there is still ringing on the rising and falling edges, and ripple on the top. Surprisingly, a decoupling capacitor is shown connected to the 5V supply.

This is not something I normally expect to see in a linear circuit, but after seeing it I realized that the switching circuitry in the zero-drift circuitry may demand variable amounts of current.

My circuit does not have a decoupling capacitor. Adding one will be a chore, but I will figure something out if it will help. Could the absence of a decoupling capacitor be compromising my signals? It is not described anywhere in the data sheet. Thanks for your assistance.


AD8628/29/30, thermopile application, power supply decoupling?




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