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I am not sure to undenstand correctly: do you mean pin 4 of JP3 to GND?But i did connect the 4 pin (Channel 2 with amp, IN -) to GND of the microcontroller [...] Can i connect one pin of the sensor to IN+ and the other pin to GND?
The best cable for this connection is a twisted shielded pair, but given the short distance it really doesn't matter that much; if you want to improve in this area just twist yourself your wires.About the cable to connect the sensor, its a simple 15cm jumper cable not shielded..but i isolated it with isolator tape (worse wont do..).
I am not sure to undenstand correctly: do you mean pin 4 of JP3 to GND?
In this case the opamp is saturated near VCC, and what you are measuring is just the ADC+circuit noise.
By the way: I found (here) that reducing the damping resistor enables you to trade-off sensitivity vs corner frequency.
So, in the end, your original circuit with 0 ohm input impedance (I/V converter) is quite smart ;-)
The best cable for this connection is a twisted shielded pair, but given the short distance it really doesn't matter that much; if you want to improve in this area just twist yourself your wires.
I only have this specifications:Several people have asked this question, but I haven't seen it get a response: what is the output impedance of the sensor? Are you connecting directly to the coils in the geophone, or is there some kind of internal conditioning circuitry?
If you're feeding directly to a transimpedance amp, that may be good for gain and bandwidth, but depending on the output characteristics it may be terrible from a noise perspective.
The preamp part of the schematic doesn't really make sense. R1 does absolutely nothing in this circuit. The coil is virtually shorted, so it will be very overdamped.The original schematic:
http://www.infiltec.com/seismo/inf-qmsd.gif
That link doesn't work, I assume you're referring to this page: **broken link removed**I only have this specifications:
**broken link removed**.
I assume you're referring to this page: L15B Geophone
I measured the resistance on the geophone, from my cheap/non precision multimeter it gave me 374ohm..which is close to the 380ohm from the specifications. About the calculations..i will take some time to do thatThat's a start anyways... it lists several possible values for the coil resistance; you should measure the resistance of the coil to see what it is. Once you know that you should do some noise calculations to determine whether the noise on the ADC you're seeing can be explained by the thermal noise of the coil, and by preamp noise. You'll should take your noisy ADC data and do a DFT of it and figure out what the spectral noise density is (in V/sqrt(Hz)).
It's not so complicated. Are you able to at least able to find out the DFT of the ADC data?Thanks for fixing the link mtwieg.
I measured the resistance on the geophone, from my cheap/non precision multimeter it gave me 374ohm..which is close to the 380ohm from the specifications. About the calculations..i will take some time to do that
Both of these circuits use a noninverting amplifier as a first stage as I suggested, so I bet they'll work better. But still the most important part of the circuit will likely be the very first amplifier stage. The amplifier should have very low noise in your band of interest; the op amp you have might be fine, but I'm not really experienced in very low frequency amplifiers.So while this circuit works, the choice of components and the circuit design is no suitable for the sensor specifications. Will it be possible to achieve good results with this circuit replacing some components or should i start looking a new one? Available schematics to these applications are so rare and i dont know how to design one..
Some available schematics (usually for ~9k ohm coil):
**broken link removed**
**broken link removed**
When you put JP3 pin 4 to GND you create a DC voltage between the inputs of U$4.if i put the pin 4 of JP3 to GND..the results start at 8million and i have much lower noise
Changing the dumping resistor from 2.7K to 3K will make no difference.do you think replacing the 2.7k ohm resistor for the original 3k resistor will do any difference?
don't worry: everybody does mistakes, but are the professionals those who make the most expensive ones ;-)Sorry for asking for confirmation, but i had bad examples in the past involving electronic experiences
Yes, the modification is exactly as you draw it .
As for the resistor: unconnect the wire from JP3 pin 4 and solder the resistor there (between the wire and JP3 pin 4).
P.S. don't worry: everybody does mistakes, but are the professionals those who make the most expensive ones ;-)
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