| ??? 12/05/06 15:45 Read: times |
#129008 - Offset voltage too high Responding to: ???'s previous message |
Dear Oliver,
The INA116 worst case offset voltage is 2mV, or 5mV for the lower grade part. This is an enormous error source on a 5mV signal, so I would definitely use a bigger resistor, even if it's only 10Mohm. Yes, you're right. I didn't pay attention to this problem. Datasheet stated that at room temperature offset error typically 0.5mV/G. For instance, if I set gain of IA to 10 then the offset will be: +/-0.5 * 10 = 5mV. So I have 2 choices here. 1/Increase resistance of the shunt resistor as you suggested. 2/Stick with 10Mohm and increase gain by 10 which will give me the result with +/-5mV offset. Your schem seems to be more accurate because the error is less due to gain is 10 times smaller. Oliver, can you tell me how to form such as large resistance with minimal components? The reason is the more components the more traces and chances of leakage current, and impedance to work with. In addition to that guarding circuit will grow as the size of the circuit grows. I have thought of using some transistor of some sort of devices such MOSFET in offstate whose resistance will be very high up to 10^6 or even higher as shunt resistor. Is it possilbe to do that? It may cause problem due to temperature coefficient of the device huh? It ia all very well that "My test will be done in the place ambien tempurature will not change a lot" is that true for the units where the "tested" diodes are used too? have you considered that????
ever so often someone get excellent results in the lab and then post "my tested units fail in the field" BALONEY, if they fail in the field, once more the faulty concept of "testing" as "proof" is shown. Erik, Yes, the "tested" diodes will be in the field where temperature always around 70 deg Fahrenheit or a bit lower. Best regards, T.L |
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