I would like to ask; is it necessary to connect the external battery when checking the "test communications"?
I tried to directly connect several times by using RS-232, but it kept failing.
Would you give me the possible solutions?
RS-232 does not provide any power to the data logger. For such a connection, you need external power connected to the data logger.
Data logger models with a USB port can operate in a limited mode with power from the USB connection.