9215 wire connection for single ended voltage signal

[KT123]

From the NI9215 operating instruction and specification file, I have learnt about the following:

Connecting Single-Ended Voltage Signals to the

NI 9215

To connect single-ended voltage signals to the NI 9215 with screw

terminal, you must also connect the ground signal to the COM

terminal to keep the common-mode voltage in the specified range

I am doing a swept sine measurement and the terminal that I am going to connect to the NI 9215 is single ended. May I know if it is compulsory to make the connection from ground signal to the COM terminal? how will it affect my swept sine measurement?

Thank you. 

[AdnanZ]

You should read this article and have a look at Table 1:

Field Wiring and Noise Considerations for Analog Signals