741 0pamp ic amplification problem

[shibas]

Iam using a vibration analyzer or sensor.I need to amplify the above sensor's output signal.For this purpose i used opamp ic 741 in the non inverting configuration.But when i gave the input to the amplifier from a function generator the amplifier gave a gain of about 50 and 68 initially.When i changed the input frequency from the function generation to 1 khz amplifier gave a gain of 100 even though the amplifier circuit was originally designed to give a gain of about 101.

But for my application,when i give the input to the amplifier from the output of the vibration analyzer the gain of the amplifier circuit changes to a huge value of about 450.

What may be the reason for this?

At first i used AD620 ic for the amplification instead of the op-amp ic 741.The behaviour of the gain at that time was also similar to now.

Somebody please help and reply fast.