EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: spintinas on February 25, 2018, 03:59:16 pm
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Hello dear colleagues, i have some questions for you about signal filtering. I want to project daq for my pressure transducer. Firstly, I have a signal from transducer (voltage about 30-60mV), then i design differential amplifier with gain of 20, and the output voltages transducer now are 500mV-1,1V, but when get a signal in osciloscope, there are a lot of noise. So, the question is, what filter is best to use for this type of signal (pressure transducer), also I want to know when it is better to filter signal? Before amplification or after differential amplifier?. I read some information on the internet and I understood, that one of the option for this situation is passive low pass (RC) filter, but I didnt know what value of cutoff frequency should be, and also low pass filter will attenuate my useful signal. So, guys, I would be thankful if you suggest some solutions.
Transducer datasheet: http://technel.com/Files/AB-HP.pdf (http://technel.com/Files/AB-HP.pdf)
Differential amp schematics is attached, i use LM324, instead LMC6484.
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1) You have a differential amplifier whose performance is highly
dependent on resistor accuracy (ratio accuracy) to reject common
mode noise. I would advise you use an IA vs roll your own. This
is an excellent treatise on the use of IAs.
http://www.analog.com/en/education/education-library/dh-designers-guide-to-instrumentation-amps.html (http://www.analog.com/en/education/education-library/dh-designers-guide-to-instrumentation-amps.html)
2) Generally a low pass filer is desired, you trade off its BW versus settling time
when you design. Use TI filter designer, or Analog Devices, to do the design.
http://www.ti.com/tool/filterpro&DCMP=hpa_amp_general&HQS=NotApplicable+OT+filterpro (http://www.ti.com/tool/filterpro&DCMP=hpa_amp_general&HQS=NotApplicable+OT+filterpro)
http://www.analog.com/designtools/en/filterwizard/ (http://www.analog.com/designtools/en/filterwizard/)
What are you doing with the result ? Here is a digital filter and differential A/D approach to
a bridge sensor problem. Note its shown as single ended, differential is just a setting. A/D is
20 bits so can look at a bridge directly in most applications. Cypress PSOC 5LP family.
(https://hackster.imgix.net/uploads/cover_image/file/85732/Capture1.PNG?auto=compress%2Cformat&w=900&h=675&fit=min)
Here is the board you would use to proto -
(http://www.cypress.com/sites/default/files/inline/fckImages/myresources/CY8CKIT-059.jpg)
http://www.cypress.com/documentation/development-kitsboards/cy8ckit-059-psoc-5lp-prototyping-kit-onboard-programmer-and (http://www.cypress.com/documentation/development-kitsboards/cy8ckit-059-psoc-5lp-prototyping-kit-onboard-programmer-and)
Regards, Dana.