The Voltcraft Plus 4080 LCR Meter Dual Display comes with an optically coupled serial interface.
You can access the device with, for example, CuteCom. The protocol is basically human readable.
The description of the commands you find at Conrad.
When the device does not respond it might be in setup mode. You can see that in the display. But the software can not. So it might be a good idea to do an initialization with [BXXXXXX] to stop the setup mode. This only works for a setup mode that was requested by an earlier remote session. You can not leave a manual setup mode this way.
Some findings not mentioned in the protocol definition above; without waranty:
and says RS232 in the display
Keys on device are disabled
Keys on device are enabled
The device complete with rubber bumper and optical/serial cable:
Screenshot of a short terminal session using CuteCom: