![]() Many students seem to find these terms helpful in first mastering the distinction between sourcing and sinking despite (or perhaps because of!) their informal nature. A device that sources current to another “blows” current toward the other device.Ī device that sinks current “sucks” current from the other device. In every circuit formed by the output channel of a PLC driving a discrete control device, or by a discrete sensing device driving an input channel on a PLC, one element in the circuit must be sourcing current while the other is sinking current.Īn engineering colleague of mine has a charming way to describe sourcing and sinking: blowing and sucking. These terms really only make sense when electric current is viewed from the perspective of conventional flow, where the positive terminal of the DC power supply is envisioned to be the “source” of the current, with current finding its way “down” to ground (the negative terminal of the DC power supply). If you focus your attention on this one wire, noting the direction of conventional-flow current through it, the task of determining whether a device is sourcing or sinking current becomes much simpler. Note 2 : By “control wire,” I mean the single conductor connecting the I/O card channel to the field device, as opposed to conductors directly common with either the positive or negative lead of the voltage source. ![]() The terms “sourcing” and “sinking” refer to the direction of current (as denoted by conventional flow notation) into or out of a device’s control wire (Note2).Ī device sending (conventional flow) current out of its control terminal to some other device(s) is said to be sourcing current, while a device accepting (conventional flow) current into its control terminal is said to be sinking current. Discrete output cards for PLCs also typically have 4, 8, 16, or 32 channels.Īn important concept to master when working with DC discrete I/O is the distinction between current-sourcing and current-sinking devices. As with the schematic diagram for a discrete input module shown previously, the schematic diagram shown here for a discrete output module reveals the componentry typical for a single channel on that card.Įach output channel has its own optocoupler, driven by its own unique memory register bit inside the PLC’s memory. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |