Hi, I'm using a sensor connected to a amplifier of gain 100... But the output gives me only about 20-50mV Vpeak... How can i make the output to have at least 1V Vpeak?

Do i have to add another amplifer?

 

Yes, or increase the gain of the existing one - assuming that's possible.

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Hi,
Whats the sensor type/specification, some sensors expect/require certain opa configurations?

Eric

 

Hi,

The sensor is NVE AAH002-02 magnetic sensor... Its a spintronics based sensor...

This is the datasheet for the sensor and the amplifier that i'm using,

Sensor: http://www.nve.com/Downloads/catalog.pdf

Amplifier: http://focus.ti.com/lit/ds/symlink/ina118.pdf

How do i check whether its possible to increase the gain of the existing one?

S.K

 

Using the gain formula from the IC data sheet, G = 1 + 50k/Rg, if you make Rg = 50 Ohm, the gain will be 1000.

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Len

 

I see... But how do i know whether the Vpeak will be at least 1V?

Isit if i get 20-50mV now using 100 gain, i multiply it by 10 to get the gain of 1000? Than i will know the value of Vpeak using the gain of 1000?

 

hi,
As Len says, use a 50R gain pot, this will give an overall gain of 1000.
If you got 50mV peak at *100, you should get 500mV at *1000.

What are you going to do with the 500mV signal?

If you must have a 1Vpk signal, then add another non inverting OPA to the output, a gain of *2 should give you 1Vpk.
Or use a 25R gain pot setting for a gain of 2000.
Check the datasheet for the Vout limits at a gain of 2000!!

What sensor bridge excitation voltage are you using?


Eric.

 

Hi,

Oh... Thats how i get the value at gain 2000.... But i cannot find the Vout limits in the datasheets for gain of 2000... Isit in the electrical specs?

I am not clear about what sensor bridge excitation voltage... Can you explain it to me?

S.K

 

hi,
Its a wheatstone bridge configuration according to the datasheet, the supply voltage is the bridge excitation voltage.

The output sensitivity of the sensor is rated as mV/Volt.

What is the supply voltage to the sensor and to the OPA?

Eric

 

Hi,

I see... The supply voltage to the sensor and OPA is 3V.

S.K

 

hi,
As the datasheet explains, the device is ratiometric and the mV output sensitivity is proportional to the supply voltage.

Using a low 3V supply, will give a low sensitivity. Is it possible that you can use say,+5V to the sensor and OPA in order to increase the sensitivity?

The sensor voltage max is +/-12V.

Eric

 

Hi,

So the higher the input voltage, the larger the ouput voltage peak?

S.K

 

The datasheet for the sensor states mV/Vsupply Oersteds [Gauss],,so the output signal is proportional to the supply, so yes.


Try it and see the effect.

 

hi,
Looking thru the datasheet for the sensor states minimum mV/V is 7.5mV/Oersted and maximum mV/V is 13mV/Oe.

So with your original Vsupply of 3V, you should get an output from the sensor of min=22.5mV and max= 39mV [for 1 Oe]

As your original Gain was 100, this should give an output from the OPA of 2.25V or 3.9V???? [for 1 Oe]

The linear range of the sensor is 0.6 to 3 Oe.

Your value of 20mV thru 50mVout would suggest that there is something wrong with the circuit, do you have a diagram?
and which magnetic field are you measuring?

Eric

 

Hi,

As this is a school project and the design of the circuit is not done by me (done by previous student) i do not have the circuit diagram. I was given the circuit.

I'm using the sensor together with a magnet to detect heart rate.

But when i use the sensor to detect magnetic field from a permerant magnet, the output is about 1+V to 2+V. It seems that detecting heart rate using the sensor would result in very weak output.

S.K