A
Anonymous
Guest
The digital PI tests I reported on earlier were done with an amplifier gain of 450. But the amplifier was followed by a voltage divider to match the output of the amplifier to the input of the ADC. The total gain from the coil to the input of the ADC was about 140. I wanted to know what the effect of a different amount of gain would be, so I ran a few more tests.
I used an input signal that is about 2.2 uV at the coil. At a gain of 140 this gives about 300 uV at the ADC. The least significant bit is about 600 uV so the signal level is about 0.5 LSB. The table below shows some different amounts of gain, the signal size relative to the LSB, and the signal to noise results I saw at the output of the integrator.
I could not easily increase the gain beyond 200 so I do not know if more gain would have continued to give improvement. I plan to aim for a gain of 200 to 300 in the next phase of the project.
Robert
<PRE>
Gain Signal/LSB Result
200 .7 a little better
140 .5 reference
68 .25 a little worse
30 .1 much worse
</PRE>
I used an input signal that is about 2.2 uV at the coil. At a gain of 140 this gives about 300 uV at the ADC. The least significant bit is about 600 uV so the signal level is about 0.5 LSB. The table below shows some different amounts of gain, the signal size relative to the LSB, and the signal to noise results I saw at the output of the integrator.
I could not easily increase the gain beyond 200 so I do not know if more gain would have continued to give improvement. I plan to aim for a gain of 200 to 300 in the next phase of the project.
Robert
<PRE>
Gain Signal/LSB Result
200 .7 a little better
140 .5 reference
68 .25 a little worse
30 .1 much worse
</PRE>