# Designing Sensor Interface Amplifier

Discussion in 'The Projects Forum' started by mikebro77, Nov 29, 2012.

1. ### mikebro77 Thread Starter New Member

Nov 29, 2012
3
0
Hi guys,

I have a assignment but I have no idea where to starts. so i thought if someone could give me a kick start.

Given that the precison temperature sensor produces an output voltage (VS: sensor Output Voltage) according to the equation Vs = (12mV) T°C + 1.8V
This equation can be expressed in terms of temperature (T) versus sensor Voltage (Vs).ie T=(Vs - 1.8) / (0.012)

You are to design the amplifier circuit for this sensor using any combination of inverting amplifiers, non-inverting amplifiers, summing amplifiers (No need to use all types of amplifier ) together with a 1V Reference voltage source.

The sensor voltage (Vs) and a 1V reference voltage (Vref) are the two input signal of your circuit. Your designed circuit should produce an output voltage (Vo) to indicate the temperature accordingly to the equation Vo = T/10. (°C/10)

ie. When T=0 °C, Vo= 0V and T=100 °C, Vo = 10V

I need to design a circuit using Op-amp.

I wonder if a differential Op-Amp is suitable for this as there is a 1V reference voltage .

Any suggestion would be appreciated ^^.

2. ### crutschow Expert

Mar 14, 2008
21,366
6,121
You need to design an op amp circuit with an offset voltage of -1.8V and gain sufficient to give the 0 to 10V output for the given sensor voltage variation over the given temperature change.

You can use a differential circuit, but that's not the only way. You can also use an inverting and a summing amp. As a design engineer it's up to you to not just find a solution but determine which is likely the best solution.

3. ### mikebro77 Thread Starter New Member

Nov 29, 2012
3
0
Hi Crutschow,

Attached PDF, I had design a Differential Op-Amp and a Non-Inverting + Summing Op-Amp circuit.

But I do not know if this work.

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4. ### crutschow Expert

Mar 14, 2008
21,366
6,121
The differential amp will provide 1V of offset but you need 1.8V. So you will need to scale the voltages to make that work. One way is to amplify the 1V.

The summing op amp circuit will provide an inversion of the signal which you do not want. You can make both op amps inverting types to solve that problem.

5. ### Dodgydave AAC Fanatic!

Jun 22, 2012
7,749
1,292
I dont understand your question, have you got a sensor that goes from 0C to 100C and gives out 0 to 10volts, and you want to amplify it??

6. ### tshuck Well-Known Member

Oct 18, 2012
3,527
679
Re-read the question... it states the design requirements so that the unit will output a voltage from 0V - 10V when temperature is 0°C to 100°C, given the sensor characteristics given by the OP....

With the sensor characteristics specified,
@T = 0, Vs = 1.8
@T = 100, Vs = 3V

OP needs:
@T = 0, Vs = 0
@T = 100, Vs = 10V

7. ### tshuck Well-Known Member

Oct 18, 2012
3,527
679
With the sensor characteristics specified,
@T = 0, Vs = 1.8
@T = 100, Vs = 3V

needs:
@T = 0, Vs = 0
@T = 100, Vs = 10V

This means you need to subtract 1.8V from your sensor output in order to get 0V @ 0°C.. then you must amplify this difference by 10 / (3V - 1.8V) in order to scale the output to the desired range...

8. ### mikebro77 Thread Starter New Member

Nov 29, 2012
3
0
Hi guys thanks for the input. Is there anyone could show me the design ?
like what I did on my attachment ? Thanks in Advance

9. ### ramancini8 Active Member

Jul 18, 2012
473
145
Go to the TI web and look up "Op Amps for Everyone". There is a chapter that tells how to use simultaneous equations to obtain your solution. The is a design chapter where a temp system is designed.