Most of the time operational amplifiers are considered an off the shelf product, which simply does its job in an electronic circuit. But quite often developers are surprised about unexpected phenomenons caused by the operational amplifier. Therefore it is very helpful to measure some basic parameters of the Op-Amp before it is used for a specific application.
One important parameter of every operational amplifier is its open loop gain. In the following application note, a simple method to measure the open loop gain of an Op-Amp, starting from 1 Hz, is described: