Help Please, Circuit understanding (basic)

[NotReliable]

Hi all,

Just wondering if I could grab a hand understanding this circuit, or more specifically what each individual part is/what it does?

Thanks for the help

 

[Spoon]

Hi mate.
Please can you be a bit more informative.
Is this a home work question? How much info do you need? Where did you get the circuit from?
The circuit could be explained in a few sentences or in hundreds of sentences.
Sorry if this comes across like I'm being a knob. Its not meant to be..

 

[DPG]

The circuit has two stages, both of which are inverting amplifiers with feedback. The RTD is a temperature sensor. I'm guessing the output feeds a meter or datalogger, etc. As Spoon says, give us more info

 

[NotReliable]

Hi,

It is a circuit for testing voltage and resistance, from an RTD, but im not sure what each part of the circuit does,

The question is asking me to explain the operation of the circuit

Not much info is needed maybe a paragraph per section of circuit?

Thanks for the hand

 

[DPG]

Hi,

It is a circuit for testing voltage and resistance, from an RTD, but im not sure what each part of the circuit does,

The question is asking me to explain the operation of the circuit

Not much info is needed maybe a paragraph per section of circuit?

Thanks for the hand

I don't want to provide a full written answer to this question you have been set - it would be counter-productive. I have given you a significant clue in telling you what the configuration of the circuit is - if you do a little research around this you will find out the exact operation. Do a Google search on op-amp theory (virtual earths, impedances, ideal op-amps, inverting amplifiers). Another bit of help: the circuit is conditioning (affecting) the signal input (the RTD in this case) into a suitable format to suit whatever the circuit drives.

 

[NotReliable]

Ah okay,

Just read up on that and it helps quite a lot so cheers,

It's just trying to get my head round electronics, doing a mechanical engineering course and never touched electronics except a long time ago in secondary.

Thanks

 

[DPG]

Ah okay,

Just read up on that and it helps quite a lot so cheers,

It's just trying to get my head round electronics, doing a mechanical engineering course and never touched electronics except a long time ago in secondary.

Thanks

Nice one
Daz

 

[NotReliable]

Okay I'v gotten to the point where I understand how most of it works, such as the op-amps inverting the signal so there are 2 of them to keep it positive and how they use the supply voltage to boast the signal of the input signal. But what I dont quite get is how the RTD itself gives an initial signal. The RTD changes resistance which would affect voltage but the circuit goes from the supply into the circuit before going into the RTD. The only thing I can visualize is that maybe the three lines symbol (the bottom left symbol of the circuit) is connected to the other 2 three lines symbols at the top?

Or is that completely off?

Thanks

 

[DPG]

Okay I'v gotten to the point where I understand how most of it works, such as the op-amps inverting the signal so there are 2 of them to keep it positive and how they use the supply voltage to boast the signal of the input signal. But what I dont quite get is how the RTD itself gives an initial signal. The RTD changes resistance which would affect voltage but the circuit goes from the supply into the circuit before going into the RTD. The only thing I can visualize is that maybe the three lines symbol (the bottom left symbol of the circuit) is connected to the other 2 three lines symbols at the top?

Or is that completely off?

Thanks

The RTD doesn't 'give a signal', rather it changes resistance dependent on temperature. The RTD and R1 form a potential divider (have a quick Google - not difficult to get this bit).

Work out what happens to the voltage (relative to 0v) at the juction of R1/R2/RTD when the resistance of the RTD varies.

The 'three lines' symbol always indicates ground, ie. 0V. Well, 99.9% of the time anyway - before anybody steps in and says ground can be different to 0V !

 

[NotReliable]

Thank you, I think I have everything now to finish it

 

[DPG]

Thank you, I think I have everything now to finish it

Excellent - give us a shout if you have any other questions.