automatic Wheatstone bridge ?

[nitad54448]

 Hi

I need to measure an AC signal at a given frequency and I need to remove one of its harmonics (which I do now manually by using a Wheatstone bridge). Is there an option of making an automatic (unattended) Wheatstone bridge ?

Thanks for tips

[YannC]

Hi nitad,

Without knowing more about your problem it's hard to help you.

Can you explain a little bit more about what you want to do and which hardware and software do you use.

Regards

[nitad54448]

Hi

I am trying to measure 2nd and third harmonic of an AC signal generated by Keithley 6221 (sinus, 50 mA or so) with a lock in amplifier... I need to remove the principal component before acquisition of the signal with the lock in

thanks for help

[YannC]

Hi,

Sorry but according to me, it's not possible to make an automatic Wheastone bridge easily.

Regards

[Broken_Arrow]

---

YannC wrote:

Hi,

Sorry but according to me...

---

That's funny!

"Automatic" bridge completion would take one to three EEPROM potentiometers and a balancing circuit, with feedback.  Certainly not off-the-shelf.

[nitad54448]

hi

thanks for the answer. do you have any suggestions as were to dig for the potentiometers and such ?

the frequency range should be small (1Hz to 1 kHz)

thanks again

[AnalogKid2DigitalMan]

I'm curious- how are you using the Wheatstone bridge to remove harmonics? Typically a Wheatstone bridge is used to measure an unknown resistance or impedance.

Just curious.

-AK2DM

[nitad54448]

i am not very sure how to do it (that's why I am asking questions here), some ideas are in this paper

N.O. Birge and S.R Nagel, Rev. Sci. Instrum., 58 (1987), 1465

regards

[Henrik_Volkers]

You can get PXI cards with variable resistors.... not from NI but I saw a link somewhere at the NI PXI section....

Steam punk solution : take a 10 (20) turn potentiometer with a small dc motor or an ALPS motor pot to build your bridge 

[Broken_Arrow]

---

Henrik Volkers wrote:

Steam punk solution : take a 10 (20) turn potentiometer with a small dc motor or an ALPS motor pot to build your bridge 

---

Well that would be fun to look at anyway. My idea was to use EEPROM pots, i.e. pots that are set digitally, such as those availabe from Dallas and i think Maxim, Analog Devices, etc. Build a PIC or Atmel controller to control the pots based on feedback. Use analog switches or relays (again, controlled by the PIC) to take the pots completely out of circuit or short them out, when they are not needed.