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    To amplify 0-30mV with gain 100

    I am using a pressure sensor(2smpp-02) whose output voltage range from 0-30mV ,wanted to amplify the it so that i can process it with micro-controller,
    can i avoid using instrumentation amplifier ?? as for it costing reason.

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    Re: To amplify 0-30mV with gain 100

    Hi,

    Without requirements/ specification regarding precision, frequency response, noise, impedance....and others:
    Yes.

    Klaus
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    Re: To amplify 0-30mV with gain 100

    You can build a discrete instrumentation amplifier. 2 or 3 OP circuit to get away with affordable resistor accuracy. 3 OP circuit is sketched in the sensor datasheet.



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    Re: To amplify 0-30mV with gain 100

    I think you want an instrumentation amplifier and I find it unlikely that building your own from 2 or 3 discrete opamps is going to have any cost benefit compared to buying the same thing in an IC. And it's almost certainly cheaper if you need well matched resistors in the discrete solution.

    On a super quick look this is the cheapest inst. amp on digikey and looks plausible for your application:
    https://www.digikey.com/product-deta...7TR-ND/1938193



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    Re: To amplify 0-30mV with gain 100

    If you can mount the amp close to the sensor, and don't need common-mode noise rejection, than you can use a standard op amp amplifier circuit.
    If the sensor is a long way from the circuit then you may need a differential instrumentation amp.
    Zapper
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    Re: To amplify 0-30mV with gain 100

    Using an instrumentation amplifier circuit with bridge sensors is a matter of accuracy, not only noise suppression. Single OP differential amplifier can work for low performance applications but sensitivity to resistor mismatching is a serious drawback.

    I agree with the comments that integrated instrumentation amplifier is the preferred solution, of course it depends on availability in your country.



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    Re: To amplify 0-30mV with gain 100

    (1) The pressure sensor is designed to convert a voltage by means of constant current drive

    Use the recommended CC source and INA amp configuration with any parts that satisfy your specs.!!
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

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    Re: To amplify 0-30mV with gain 100

    Yes, I didn't realize the sensor is a bridge, so you need an instrumentation amp for that.
    Zapper
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    Re: To amplify 0-30mV with gain 100

    Consider amplifying your signal by means of a transistor in common-base operation. It provides high gain.
    This simulation shows the concept.

    Click image for larger version. 

Name:	amplify 0-30mV signal commonn-base NPN output 0 to 3V.png 
Views:	9 
Size:	24.9 KB 
ID:	153223

    The aim is to get readings which are proportional to your sensor's signal. (In other words, linear performance.) To get linear performance requires careful adjustment of bias. It's typical to use a potentiometer to adjust bias voltage and resistance.

    Another factor is transistor temperature. Merely a few degrees variation changes the conductivity in the transistor. The result is to make readings a bit high or low. Therefore you need to watch your zero line, and adjust as necessary.

    - - - Updated - - -

    Your sensor needs to be able to sink a few mA.



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    Re: To amplify 0-30mV with gain 100

    Thank you for your response,
    this is the application note of the pressure sensor, I implement the same circuit which is shown on the page 10 , with little modification i.e
    1)giving GND to Reference input
    2) R6=10Kohms not 1Kohms which give me gain of 3

    https://www.components.omron.com/doc...7-bd406615a1b3

    sensor differential output is of 233mV,

    now the problem is when i switch the pump on same supply 5V and 290mA ,the sensor output voltage drop by 100mV



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    Re: To amplify 0-30mV with gain 100

    Hi,

    I wonder who designed the "Recommended Circuit Diagram" of the application note.

    In my eyes a "constant current circuit" should provide constant current regardless of supply voltage. But the given circuit does not. If the supply voltage changes by x%, then the (so called) constant current will change the same x%.
    --> Replacing R2 with ZXRE125FF (or similar shunt reference) will truly generate constant current of 122uA.

    Also the whole circuit does not include any noise suppressing low pass fiilters, nor any power supply stabilizing capacitors.
    (I´d never use this circuit "as is". It may work in laboratory environment, but may fail in the field.)

    1)giving GND to Reference input
    It should be the Reference_GND of the ADC. Wire this node directely to the ADC pin.

    2) R6=10Kohms not 1Kohms which give me gain of 3
    Makes no sense, since you worte you want gain of 100.

    I recommend to do the "high gain" with the left hand two OPAMPs, by reducing the value of R6.
    Let the right hand OPAMP have gain of 1. (unless you have frequency response problems)

    Klaus
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    Re: To amplify 0-30mV with gain 100

    I believe if what's labeled Vdd is also the ADC reference then there is an advantage to leaving the current source referenced to it.



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    Re: To amplify 0-30mV with gain 100

    The mysterious point is stated 233 mV sensor output voltage although the datasheet says it's only 30 mV at rated pressure.



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    Re: To amplify 0-30mV with gain 100

    If 290 mA was the rated current, then the surge was upwards to 3A which caused your 5V and pressure signal to drop. Replace 5V to 1V R divider with a stable reference voltage or regulator. There is a current sense of 10K below bridge. So 100uA = 1V/10k
    A best design is easily achieved with good test specs™
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    Re: To amplify 0-30mV with gain 100

    its working getting -2mV without any pressure and it increase gradually as pressure increases.
    I have change the pressure sensor , i think i have damage the first one.

    thank you everyone,

    i am still working on it as the output is too noisy,



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    Re: To amplify 0-30mV with gain 100

    Quote Originally Posted by nileshpassi View Post
    sensor differential output is of 233mV,

    ,the sensor output voltage drop by 100mV


    Serious insufficient overall design specs!!

    what medium air? fluid ?

    Max Pressure? only 37[kPa] ~ 6 psi

    233 mV is far too high for signal.

    Show all design details and measurements
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

    ... Tony Stewart EE since 1975
    - slightly north of Toronto



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