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Input SIPs on Centroid PLC Boards

Most of Centroid's PLC I/O boards introduced since 2002 have configurable inputs. Each bank of inputs (usually four per bank) can be configured for either current-sourcing or current-sinking operation, at 5VDC, 12VDC or 24VDC.

This includes the Auxiliary inputs on the DC3IO and DC3IOB, and all inputs on the PLCIO2, All-In-One DC, GPIO4D and PLCADD1616.

The operating voltage for each bank of inputs is externally supplied, usually from a separate DC power supply.

The DC3IO and DC3IOB have provision for using the internal 5VDC supply (in a current-sourcing configuration) via jumpers.

In All-In-One DC installations, the "external DC supply" is often 12VDC from the logic power supply built onto the back of the All-in-one DC unit.

In all cases, SIP ("single in-line package") resistors must be installed on the PLC board to match the operating voltage of each bank of inputs.

The SIP resistors which Centroid uses are the same on all PLC boards. They are 8-pin single-row modules, each containing four isolated resistors. They are sized to allow approximately 10mA current through a closed input point.
Input VoltageResistancePart Code
5VDC470Ω-471
12VDC1KΩ-102
24VDC2.2KΩ-222

The resistance of a SIP is coded in the part number, with "-471", "-102", or "-222". The 470Ω SIPs have a two-line part number with the rating on the first line, and a rounded "dipped" appearance. The 1K and 2.2K SIPs have a three-line part number with the rating on the second line, and a rectangular shape. Note that the first line of the part number on both 1K and 2.2K SIPs contains "-102". That is not the resistance rating. The resistance rating is on the second line.


The orientation of the SIPs in their sockets is not important. They are internally symmetrical.

SIP locations on some sample boards are shown here:


It is important to have the correct SIPs installed for the input voltage you are using.

It is particularly critical not to have lower-resistance SIPs installed, as that can allow enough current through the input to damage the opto-coupler.

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Copyright © 2012 Marc Leonard
Last updated 01-May-2012 MBL