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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, PLCADD1616 and OAK.

The RedOak, PLCEXP1616, Ether1616 and AcornSix boards use a slightly different design, described below.

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 or 24VDC from the logic power supply that runs 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

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.

AcornSix, RedOak and PLCEXP1616

The AcornSix, RedOak, PLCEXP1616 and Ether1616 boards are designed for higher current through the opto-couplers; and they have ca. 1K resistors built in, parallel to the SIP sockets.

With this design, no SIPs should be installed for 24VDC operation; and the SIPs shown below should be installed for lower-voltage operation.
Input VoltageResistancePart Code

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Copyright © 2023 Marc Leonard
Last updated 06-Apr-2023 MBL