The PLC-K522 Discrete Output Expansion Modules are offered in Transistor or Relay and 8 or 16 outputs. These modules are attached to the PLC-K5 CPUs to expand beyond the onboard outputs. The PLC-K5 CPUs can handle up to 136 I/O points with a maximum of 6 expansion modules. If a user were to select the PLC-K508-40AT along with 6 PLC-K522-16DT units, the user would achieve the maximum 136 I/O points within the constraint of 6 expansion modules. The PLC-K522-__DT modules come with transistor outputs with a sourcing configuration. A sourcing output is internally pulled down to ground; the current wants to flow into the output. The-PLC-K522-__XR modules come with relay outputs that can handle loads up to 30VDC and 250VAC. Relay outputs are great to drive AC or DC motors or turn any AC or DC device on. The transistor output modules are opto-isolated for unit protection.