Noise Spikes in my analog signal conditioner

Thread Starter

fieryfire

Joined Feb 14, 2017
150
Hello

I am observing noise spikes in my signal data every 2 seconds (as shown in image below)

My signal conditioning setup is as follows -
Strain gauge - Quarter Bridged - 350Ohm sensor
Instrumentation amplifier - AD8428
Voltage reference of 2.5 to power the bridge - ISL21090
Bipolar power supply of +-12V (Output voltage swing between -10V to +10V) via TRACO POWER - TEN HS1
filter at 300Hz using OPA4197
Analog to digital conversion using Labjack T7 at 16 bit with measurement range -10V to +10V

I have attached the schematics of the electronic design below. Could some one please mention what i am doing wrong


upload_2019-7-4_15-11-5.png
 

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danadak

Joined Mar 10, 2018
4,057
Have you gone thru signal chain origin to output looking for these pulses.
2 sec sound like a thermostat or such low period lab instrument doing
something. Or maybe lighting generated emi.

If you have a scope, DSO, trigger off rep rate or pulse width to capture
it point for point in signal; chain. Tedious but thats one way.

Is it possible USB link is doing this......not sure.....


Regards, Dana.
 

AlbertHall

Joined Jun 4, 2014
12,384
Replace the sensor with fixed resistors and see if the stray signal is still there.
Assuming no change, go through the rest of the signal path to see where the interference is coming from.
 

Thread Starter

fieryfire

Joined Feb 14, 2017
150
Have you gone thru signal chain origin to output looking for these pulses.
2 sec sound like a thermostat or such low period lab instrument doing
something. Or maybe lighting generated emi.

If you have a scope, DSO, trigger off rep rate or pulse width to capture
it point for point in signal; chain. Tedious but thats one way.

Is it possible USB link is doing this......not sure.....

Hello Danadak, I have not gone throught the signal chain, as i am unsure how to do so. The components are all tiny SMD components and i wouldnt be able to place a scope over the terminals.

Can it be that some IC maybe malfunctioning?

Also could you please explain how to do the following you mentioned. Im not sure i follow.

"If you have a scope, DSO, trigger off rep rate or pulse width to capture
it point for point in signal; chain. Tedious but thats one way."


Regards, Dana.
 

Thread Starter

fieryfire

Joined Feb 14, 2017
150
Replace the sensor with fixed resistors and see if the stray signal is still there.
Assuming no change, go through the rest of the signal path to see where the interference is coming from.
This is a good idea that i must try to build a resistor input to bridge with my system to find out where the interference comes from
 
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