The AV550 automatically turns off the power to the channel card when it is removed. You have to either cycle power to the whole unit, or use the channel card power.
To get to the channel card power menu hit the Setup Key (wrench). See below:
Select Channel card power
Select the desired channel and enable.
The AV550G Multi Channel Oxygen Analyzer System allows for measurements on up to eight ZR22 probes simultaneously. The ZR probe's in-situ measurement method does not require any process conditioning or extractive sampling, reducing maintenance costs and resulting in faster measurement response to changes in the process.