Pages: [1]   Go Down
Author Topic: Using an opamp to measure the voltage accross a RTD (SOLVED)  (Read 724 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Jr. Member
**
Karma: 0
Posts: 88
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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?  

Thank you in advance.
Regards Voidugu
« Last Edit: May 11, 2013, 06:45:35 am by Voidugu » Logged

Rapa Nui
Offline Offline
Edison Member
*
Karma: 60
Posts: 2073
Pukao hats cleaning services
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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..


* wh.jpg (10.46 KB, 365x323 - viewed 87 times.)
Logged

Dee Why NSW
Offline Offline
Edison Member
*
Karma: 47
Posts: 2268
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You want something like this?

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

Offline Offline
Jr. Member
**
Karma: 0
Posts: 88
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Thank you very much for the help people smiley
Logged

Pages: [1]   Go Up
Jump to: