The resistance temperature detector (RTD) forms one arm of the Wheatstone bridge as shown in the figure below the RTD has a resistance of

at temperature of

in formula

,

is the temperature coefficient of RTD in thermal equilibrium with the measuring temperature.

1. Determine the measuring temperature of RTD when the bridge is balanced.

2. Determine the output of voltage in the operational amplifier at temperature

.

 

its more clear on the screenshot i attached

 

hi mussa,
Welcome to AAC.
As this is homework, please post your attempt at answering, we can then guide you through the project.
E

 

hi mussa,
Your post does not answer questions #1 and #2 on the initial diagram.
Post your calculations.

E

 

hi mussa,
Your post does not answer questions #1 and #2 on the initial diagram.
Post your calculations.

E

im not really sure but check this out

 

hi,
Have you calculated the RTD resistance at 300C.?
Use the formula in the question notes.
E
Update:
Who drew the circuit diagram.?

 

hi,
Have you calculated the RTD resistance at 300C.?
Use the formula in the question notes.
E

RTD= 25(1+0.003925 x 300) = 54
how about question 1 R2 in my case and R1 in the question how to deal with that?

 

hi,
Have you calculated the RTD resistance at 300C.?
Use the formula in the question notes.
E
Update:
Who drew the circuit diagram.?

our teacher

 

hi,
Q1 does not make much sense.?
Consider if I chose 0C to be the balance temperature, I would adjust VR1 until the Vout =0V
If I said I chose 25C, I would adjust VR1 for Vout=0V.

Does the tutor realise that as the RTD resistance increases with temperature, the Vout is driven negatively.?
So the the OPA must have dual supply voltages.

If a single supply voltage is used the INV and Non INV inputs to the OPA should be changed over.

E

EDIT:
Added a LTSpice simulation to show the results.

 

my bad i missed this part (the value of the variable resistance R1 must be set to 41.485 ohm to balance the bridge circuit

 

from this i can say RTD is

hi,
Q1 does not make much sense.?
Consider if I chose 0C to be the balance temperature, I would adjust VR1 until the Vout =0V
If I said I chose 25C, I would adjust VR1 for Vout=0V.

Does the tutor realise that as the RTD resistance increases with temperature, the Vout is driven negatively.?
So the the OPA must have dual supply voltages.

If a single supply voltage is used the INV and Non INV inputs to the OPA should be changed over.

E

EDIT:
Added a LTSpice simulation to show the results.

View attachment 180196

the question gave or set R1 to be 41.485 ohm which doesn't matter as u say, bic no matter what the value of R1 be the the temperature of RTD for the balanced bridge will remain 0. In case we set R1 to be 41.485 oh, our RTD will also be 41.485 ohm. I'm i correct?

 

hi,
If VR1 was stated as set to 41.85R then for a Vout=0 the RTD would have to be 41.85R.
What do you calculate the Temperature to be when the RTD is 41.85R.??
E

 

hi,
If VR1 was stated as set to 41.85R then for a Vout=0 the RTD would have to be 41.85R.
What do you calculate the Temperature to be when the RTD is 41.85R.??
E

0c?

 

hi,
How can that be correct, when the question states RTD= 25R at 0C.??
It must be hotter than 0C.
45.85= 25(1+(0.003925*temp)).....
E

 

hi,
How can that be correct, when the question states RTD= 25R at 0C.??
It must be hotter than 0C.
45.85= 25(1+(0.003925*temp)).....
E

I see, RTD's temperature is 209C, then for question 2 at temperature of 300C RTD is 54 ohm to find the output voltage at that temperature what shall i do?

 

hi,
Sorry I made a typing error
45.85= 25(1+(0.003925*temp))..... that should be 41.85R, so recalculate the value.

To calculate Vout, calculate the Gain of the OPA amplifier, do you know how to do that.?
E

 

hi,
Sorry I made a typing error
45.85= 25(1+(0.003925*temp))..... that should be 41.85R, so recalculate the value.

To calculate Vout, calculate the Gain of the OPA amplifier, do you know how to do that.?
E

its 41.485 = 25(1+0.003925*t)) = 168C
i know gain is output/input voltage, but in this we are asked to find output voltage?

 

hi.
You can use this equation for bridge, see image.

The way the question is written does not make sense to me.

If the bridge is being use to measure temperature, the RTD would be 25R at 0C, the RV1 trimmer would be set to give 0V output from the bridge.

If you the heated the RTD to say 168C, the RTD would have a resistance of 41.485R.

You would then use the equation with those values to find the bridge Vout.

E

 

hi,
If you look at the plots in post #10, you will see that the OPA amp saturates at -12V at approx 140C.

It is also a negative going output, which means the OPA must have dual supplies.

My advice would be to go back to your tutor and ask for a better worded question and an OPA amplifier design that works for the questions.

E

 

hi,
If you look at the plots in post #10, you will see that the OPA amp saturates at -12V at approx 140C.

It is also a negative going output, which means the OPA must have dual supplies.

My advice would be to go back to your tutor and ask for a better worded question and an OPA amplifier design that works for the questions.

E

will do that thanks a lot