Noise hardening transmission

In summary, the analog device instrumentation amplifier has been designed to amplify low-level signals and provide noise rejection. The amplifier has a non-inverting voltage amplification stage and can be used with a variety of cables.
  • #1
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I have a very small signal coming from a thermocouple [tex]\mu V \mathrm{to}\, nV[/tex] range, which gets drowned in noise when I transmit it via a 2m BNC cable, even the lock in runs into problems.

I am about to amplify it at the source, and while I am at it, I will try to do a few more tricks. Electronics always contained a fair amount of voodoo to me, so maybe someone here with some ee intuition can tell me what works.

Some info about the signal.
1) Anything above 500Hz is noise
2) A crappy passive R-C lowpass did not do enough to clean the signal
3) Voltage levels are ok up to 1V at the receiver.
4) The signal must go into a very high impedance, since it cannot provide any appreciable power.
5) We are working in fairly high magnetic fields

So the maximal setup I came up with is this (in order how the signals passes it):

1) active 500Hz lowpass
2) Amplifier 1000x ?
3) split the signal and invert it
4) three pin lemo plug for ground and +/- Signal
5) Cat 6 STP cable put +/- on one pair ground on another one
6) two active 500Hz Low passes
7) then into the differential input of the Lock in

But since I don't understand much about the tricks of the trade I don't know where the problems would be.

So my thoughts about the different components so far:
1) The initial low pass is just there because I see no point in amplifying something that I know is noise. I was told this could lead to a DC drift, which should not cause a problems if we are talking less then 1[tex]\mu V/\mathrm{day}[/tex]. I hope this element does not produce noise, distort, or draw current.

2) This sounds like a job for an op amp with a non inverting voltage amplification set up. Is there a reason to limit oneself to some amplification. Can I just do 10^6 or so.

3) Here I am really confused. I didn't see any setups for this. I would expect this to be a common task for differential signal transmission. But somehow they always seem to use two wires against ground, not caring about the symmetry. (So we know the difference between the wires, but we leave the voltage to ground floating) Voltage inversion seems to require some finite impedance at least with the inverting amplifiers that I saw.

4) Lemo is niiiice, I like, expensive though

5) I have little clue about cables. Is it better not to ground one side of the signal, and not use the shield as the return path. What are good cables? I was also thinking about triax, but there the wires are not balanced, so I don't think that they are suitable for differential transmission. Is that correct?

6) DC drift again, I hope I can get rid of it by pushing the "relative" button of the meters in the morning...


Questions:
1) Do you see problems with the above set up?
2) Do you have recommendation for parts?
3) Do you know a box that I can buy that does what I want?
4) What Do you think will give the greatest noise reduction? Early amplification, differential transmission, good cable, frequency filters, avoiding shield as return path?
5) If it's all build in house, how much work and time do I have to expect, for placing magical capacitors and tuning the resistances...

Any help appreciated
 
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  • #2
Both signals should be in the same coax. I have used RG-108 twinax with success. Be very careful of multiple grounds, including building grounds and ac power grounds.. Use a good grounding strap to connect various chassis together. I have used low-noise opamps (< 5 nV per root Hz), or about 50 nV for 100 Hz BW. I favor a inverting amplifier configuration, but be sure to use 4 resistors for common-mode noise rejection.

Analog Devices has a full selection of instrumentation amplifiers and isolation amplifiers. Here is one common instrumentation amplifier.
http://www.analog.com/en/amplifiers...tation-amplifiers/ad622/products/product.html
 
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  • #3
You can also incorporate gain and filtering in a fully differential MFB stage such as described in the following link

"focus.ti.com/lit/an/sloa064/sloa064.pdf"[/URL]
 
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1. What is noise hardening transmission?

Noise hardening transmission is a method used in electronic systems to increase the durability and reliability of signal transmission by reducing the effects of external noise interference.

2. How does noise hardening transmission work?

Noise hardening transmission works by introducing techniques such as shielding, filtering, and error correction coding to mitigate the impact of noise on signal transmission. These methods help to increase the signal-to-noise ratio, making the transmission more resistant to external noise interference.

3. What are the benefits of noise hardening transmission?

The main benefit of noise hardening transmission is improved reliability and robustness of electronic systems. By reducing the impact of external noise interference, it helps to ensure that signals are transmitted accurately and without errors. This is especially important in critical systems such as communication and defense systems.

4. When is noise hardening transmission necessary?

Noise hardening transmission is necessary in any electronic system that is susceptible to external noise interference. This is particularly important in systems that require high levels of accuracy and reliability, such as medical equipment, aerospace systems, and industrial control systems.

5. What are some common techniques used in noise hardening transmission?

Some common techniques used in noise hardening transmission include shielding, filtering, and error correction coding. Other methods such as frequency hopping and spread spectrum techniques may also be used to reduce the impact of external noise interference on signal transmission.

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