I know if you reverse + and - on a voltage supply you can measure a negative voltage using a multimeter, but for an op amp they only have one negative pin so I don’t think reversing + and - would work because you would be connecting the - voltage terminal to ground, I’m a little bit confused about how to achieve this, could you please explain how to get a - supply rail Thanks, Be
Use a DC-DC converter, a charge pump capacitive inverter or an inverting buck converter. Some type of switching supply is the easiest approach if you only have a positive rail available and actually require a negative rail.
There are easily available DC-DC converters that will accept a single DC voltage input and produce (say) +/-15V rails that are galvanically isolated from the input.
It's easier for your meter because it has an inherently isolated supply in the form of the battery.
You may find this thread helpful.
I would suggest you to do it with two batteries as shown below. However, your question lacks detail, so I can't recommend what would be the best possible solution for you.