CNC controller no analog voltage output

Before the CNC controller connect to the spindle inverter, there was 0~10V analog voltage output, but after connected to the inverter, the analog voltage getting very small, input spindle speed command to the highest on the CNC controller, but there was output less than 10HZ, obviously it is abnormal.

It might be the inverter not compatible with the CNC controller, for example, the voltage, current, or resistance value, they were not match to each other. (From http://www.CNCmakers.com)

In this case adding a 100K Ohm resistance between CNC controller and spindle inverter in series connection, the spindle inverter works fine.