The internal +24v power supply voltage range is 20v~28v, and the maximum
working current is 100mA. If an external 24V power supply is used, please connect
the external power supply +24v to DM and the external power supply 0V to 0V.
A power supply for DO output should be prepared by customers. The power
ranges 5V~24V. The maximum allowable voltage is DC30V and current is 50mA.