The 2500-R4500 is designed to replace various older style of Texas Instruments Programmable Controllers (520/530/530C/530T) and/or Distributed Base Controllers. The 520/530/ DBC units are commonly referred to as “oil pan” or “sump” units due to their boxy shape with ribbed fins. The 520C/530C/530T programmable controllers (520C-1101/1102, 530C-1102/1104/1108/ 1112, 530T-1104/1112) attached to the I/O base through the 500-5840 adapter base.