How to Increase Vibration Sensor Output Using Op-Amp or Signal Amplifier?

How to increase sensor output?

As for the 741 op-amp, you need to look at the frequency aspects - roll off rates. Go look at the spec ( frequency plot ) and you will see as the frequency goes up the gain goes down. If I recall correctly somewhere around 100KHZ the gain drops to one. So you telling me that the gain was correct around 1 KHz does not surprise me. You need to determine the highest frequency you expect and then find a device that will work at that frequency. The 741 op-amp is not a high frequency device.

Yes, it's a little thing called Gain Bandwidth Product:

http://en.wikipedia.org/wiki/Gain–bandwidth_product

BW = A*GBW where _BW_ is the bandwidth, _A_ is the gain, and _GBW_ is the Gain Bandwidth Product.

In your example (which, strangely, is not showing above, yet is present in the email I received), when the input signal freq was 9.7KHz you measured a gain of ~50 for a GBW of 9.7K * 50 = 485KHz, which conforms with the low end of the spec for a 741. So, if the GBW of your 741 is 485KHz then at 1KHz, you can expect a maximum gain of 485KHz/1KHz = 485, thus your measurement of a gain of 100. I would chalk the variance from 101 to experimental error (i.e. resistor tolerances, measurement error, etc.)

The max frequency or bandwidth spec of an opamp is usually the _Unity Gain_, i.e. the gain at 0Hz or DC.

If i insert a low pass RC filter in between the vibration sensor output and the 741 op amp input will the gain become alright?I think some times the vibration sensor output will be at very high frequencies.So a low pass RC filter may remove these high frequency components.

It all depends on how responsive you want your sensor to be.