In an ion sensor head (300-I) and a smart handheld meter (WQ-300) with the following firmware versions, there is no option to select an ion sensor cartridge. Then, it is necessary to update the firmware of the ion sensor head or the smart handheld to the latest version. Make sure to check before using an ion sensor cartridge.
Ion sensor head: 1.0.0
Smart handheld meter: 1.0.0, 1.0.1, 1.1.0
Refer to the instruction manual for smart handheld meter on how to check the firmware. It is possible that these firmwares will be updated from time to time as new functions and improvements are made. Check the following links for how to obtain the latest firmware and how to update the firmware.