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### Topic: Using an opamp to measure the voltage accross a RTD (SOLVED) (Read 2322 times)previous topic - next topic

#### Voidugu

##### May 11, 2013, 10:00 amLast Edit: May 11, 2013, 01:45 pm by Voidugu Reason: 1
I am trying to measure the voltage drop across an RTD. Its resistance will vary from 50 to 100 ohms. A resistor of 75 ohms connected in series with the RTD, creating a voltage divider,connected to 5V DC gives a voltage range from 2V (R RTD = 50 ohms) to 2.857V (R RTD = 100 ohms) across the RTD. If this was fed directly to the ADC of the atmega328 then the resolution would be extremely poor.

My idea is that with a suitable amplifier circuit, this voltage range can be amplified around 5.83 times (5 /(2.857 - 2)= 5.83)to allow me to utilize the full potential of the atmega's ADC. The problem is that i am a complete novice with opamps since this is the first time using them.

Could you please help me by providing a suitable circuit or by providing me with some information on how to implement this?

Regards Voidugu

#### pito

#1
##### May 11, 2013, 10:32 am
Just an idea: you may use Wheatstone bridge (see below). Wit R1/R2 you may zero the bridge (you get zero at the opamp output), the op-amp amplification (you need a proper op-amp circuit there) gives you the range (ie. 0V-5V).
Google "wheatstone bridge op amp circuit" to get some details on it..

#### Nick_Pyner

#2
##### May 11, 2013, 10:40 am
You want something like this?

http://openenergymonitor.org/emon/node/75

#### Voidugu

#3
##### May 11, 2013, 01:44 pm
Thank you very much for the help people

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