The letter "U", often used to denote voltage supply, is said to be derived from the German word "Unterschied" which means "difference". This loosely implies "voltage difference" which may be used to help understand the meaning of the use of the letter "U" for the power supply to these types of electrical equipment.
For the IFM IO-Link Master devices, a distinction is made between two supply voltages:
– U
S to supply the communications power and the sensors (always required)
– U
A for supplying the actuators, only required for devices with fixed outputs or for additional devices
Power supply U
S is required to supply the communications power of the device electronics and to supply the sensors.
It must be connected to every device. If this supply voltage is disconnected, the device will not work.
This is the recommended installation wiring method:
- Install the power supply for the device electronics (U
S)
independently of the power supply for the actuators (U
A)
- Protect the power supplies
independently. This means that the bus can continue running even if some I/O devices are switched off.
The voltage supply U
A is only required for the supply of the IO-Link actuators. The IO-Link port, when in the operating mode "DO", is supplied via U
S. If an IO-Link device is not using any actuators then the supply U
A need not be connected.
As mentioned, it is good practice to separate these supplies so as to better protect the more sensitive device electronics and communications bus on U
S from the potentially higher current rated actuator devices on U
A.
However, I have seen quite a few of these installed with a single power supply connected to both U
S and U
A, especially when the power supply is local to the IO-Link device enclosure, where space is often at a premium.
alive15 said:
...I see why you would want to separate power between inputs and outputs; the UA is similar to having like a Master Control Relay or Control Power, correct? So when the UA or the Control Power is turned off, I would have no outputs on like in a PLC output card, but my input devices will still have power to them so I will still see the inputs on in the PLC input card. Correct??...
The manufacturer's advice to protect sensitive electronics, by use of independent powers supplies, is the primary reason for the option being available, more so than facilitating auxiliary functions, such as isolation of outputs while inputs remain on, or ad hoc safety isolation. I'm not saying you cannot use this option for such things, but just that it is not its primary reason for existing.
Regards,
George