Originally posted by WM6
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moodz.
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I had a look at the input to the diff amp post the clamping diodes and I cannot see the "bump" however there is a fast transitiion "spike" at this point where the clamping diodes stop conducting. One of the reasons the diff amp is DC connected to the coil is because it needs reference bias on its inputs ( see data sheet ) in order to operate. Because the coil centre tap is connected to analogue ground ( VPP ) this provides the bias to the amp. It is possible that the amp only starts working properly after the diodes stop conducting ... not sure. I think I will leave it till I get to a more advance input scheme like active clamping as Carl had suggested.
moodz. -
Not bad really.
Interesting to know if ideal balanced (without bump) can give better or worst deflection rate.Leave a comment:
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sample target info
I am using a coil with 32 turns / 22 cm dia. It appears to have a 20 usec decay.
The amp gain in this case is set to 100 not 1000 as there is too much gain at this setting.
The trace below shows a plot for target / no target. The purple trace is the no-target reference trace. The target is an australian $1 coin ( .... this is not a gold coin BTW ) and was placed in the centre of the coil.
There is about 200mV of deflection caused by placing the target coin. IMHO this is quite good.
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The little bump you see is a result of slight imbalance. There is no target in this shot. The bump comes from slight underdamping on input ... it can be tuned by playing with damping resistor value and balancing capacitance on differential coil A / B leads however it will still work fine for sample and hold purposes.Originally posted by WM6 View PostLeave a comment:
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Waveforms + Measurements
Representative waveforms at the output of the diff amp.
The pulse repetition frequency is quite high at 5.3 kHz however in this application the DSP code needs the high rate for adequate sensitivity.
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