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The input signals share a single signal common return. For good noise immunity, establish system signal commons, power supply reference points, and grounds close to such single-ended points. Signal common (as defined by most Standards) for the input module is the negative side of the 24 volt supply. The module’s chassis ground goes to the I/O Terminal Block ground terminal. To improve noise immunity, connect this to the enclosure chassis with a short length of wire. Two wire loop powered transmitters (type 2) should have isolated or ungrounded sensor inputs. Loop powered devices should use the same power supply as the input module. If a different supply must be used, connect the signal common to the module common. Also, ground only one point on the signal common, preferrably at the input module. If the power supply is not grounded, the entire analog network is at a floating potential (except for the cable shields). Thus this circuit can be isolated if it has a separate isolated supply. If shielded wire is used to reduce noise pickup, the shield drain wires should have a separate path to ground from any loop power supply ground to avoid inducing noise due to drain current. Three wire transmitters require a third wire to provide power. The shield may be used as the power supply return. If the system is isolated, a third wire (triad cable) should be used instead of the shield for the power, and the shields grounded. A separate, remote power supply can also be used. A floating supply should be used for best results. Grounding both supplies creates a ground loop. The circuit may still work despite this, however achieving good results requires very good voltage compliance of the transmitter. Isolated 4 wire transmitters can avoid ground loop problems with remotely powered sensors. If the module is installed on an I/O Terminal Block with Box Terminals or an I/O Terminal Block with Barrier Terminals, an Auxiliary Terminal Block must be used to provide additional wiring terminals. For the I/O Terminal Block with Wire to Board Connectors, external connection points are usually preferred, although an Auxiliary Terminal Block can be used. Auxiliary Terminal Blocks have all terminals connected together internally. The Auxiliary Terminal Block with box terminals has 13 terminals, each of which accommodates one AWG # 14 (avg 2.1mm2 cross section) to AWG #22 (avg 0.36mm2 cross section) wire, or two wires up to AWG #18 (avg. 0.86mm2 cross section). The Auxiliary Terminal Block with barrier terminals has nine terminals, each of which can accommodate one or two wires up to AWG #14 (avg 2.1mm2 cross section). For 3-wire and 4-wire transmitters, an I/O Terminal Block with box terminals and Auxiliary I/O Terminal Block can be used without any additional terminal strip. An additional terminal strip is needed for an I/O Terminal Block with barrier terminals and an Auxiliary Terminal Block. The +24V Out terminals are a common fused output from DC+ to drive loop–powered 2 wire sensors. For anything other than 2-wire transmitters, jumper the Auxiliary Terminal Block to DC–.