wxstevens
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- Cool Ridge, WV
Does anyone have an explanation of DC Sink? I have to deal with some 5/04's and most of the I/O's are printed with that on the front. Thanks.
Allan-Bradley PLC
- Thread starter wxstevens
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mcclary's electrical
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- VA
wxstevens
Member
- Location
- Cool Ridge, WV
Any idea what the "sink" means?
mcclary's electrical
Senior Member
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- VA
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- Wisconsin
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- PE (Retired) - Power Systems
Very basically, sink and source are terms used with solid state devices to describe whether they have a +DC or a -DC switch leg.
There has always been confusion with PLC cards. Some manufacturers tell you their card is a sink, in which case the common is negative and your I/O needs to be a positive. Other manufacturers tell you to wire their card to a sink in which case the common is positive and your I/O is a negative signal.
There has always been confusion with PLC cards. Some manufacturers tell you their card is a sink, in which case the common is negative and your I/O needs to be a positive. Other manufacturers tell you to wire their card to a sink in which case the common is positive and your I/O is a negative signal.
StephenSDH
Senior Member
- Location
- Allentown, PA
The terminology gets confusing. You probably have a 1746-IB card as opposed to the 1746-IV Sourcing Input Card. The sinking/sourcing terminology is used for the output cards also. It determines where the +DC voltage is supplied in the circuit. The American norm is Sinking Inputs and Sourcing Outputs. Crazy Europeans will commonly use Sourcing Outputs and Sinking Inputs.
Sinking Input: Sinking input requires Sourcing Field Device. +DC voltage is wired to the field device. When the switch is closed +DC is applied through the field device to the input point energizing the input. When the switch is open the input voltage returns to -DC turning off the input.
Sourcing Input: Sourcing Input requires Sinking Field Device. +DC voltage is supplied from the input point. The field device is wired to the input point and -dc. When the switch is closed the input point is pulled down to -DC by the field device and energizes the input. A resistor in the input card limits the current so the input point is easily pulled down to 0 VDC. When the field device turns opens the input returns back up the +DC and the input point is off.
In both cases there is current flow which lights up the led light on the input card. The current flows opposite directions for sinking inputs verse sourcing inputs.
Sinking Input: Sinking input requires Sourcing Field Device. +DC voltage is wired to the field device. When the switch is closed +DC is applied through the field device to the input point energizing the input. When the switch is open the input voltage returns to -DC turning off the input.
Sourcing Input: Sourcing Input requires Sinking Field Device. +DC voltage is supplied from the input point. The field device is wired to the input point and -dc. When the switch is closed the input point is pulled down to -DC by the field device and energizes the input. A resistor in the input card limits the current so the input point is easily pulled down to 0 VDC. When the field device turns opens the input returns back up the +DC and the input point is off.
In both cases there is current flow which lights up the led light on the input card. The current flows opposite directions for sinking inputs verse sourcing inputs.
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StephenSDH
Senior Member
- Location
- Allentown, PA
The ControlLogix DC Input Modules are duel Sink/Source so the same module can be configured for either. I don't know why they didn't do this years ago.
Strahan
Senior Member
- Location
- Watsontown, PA
AB cards for the 1747 SLC modules are referred to as sink or source (AB is referring to the card). Sinking card negative common needs a sourcing input (switch the positive). Sourcing card positive common needs a sinking input (switch the negative).
Sorry it appears both replies went through! Lost connection when replying the first time.
Sorry it appears both replies went through! Lost connection when replying the first time.
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Strahan
Senior Member
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- Watsontown, PA
AB refers to its 1747 I/O modules as either sink or source. If it is a DC sinking card then the common is connected to the negative and the inputs require a positive or sourcing input. When the card is referred to as sourcing the common is connected to the positive and the card requires a sinking input (inputs connected to the negative). The card will dictate what type of I/O devices will be used. We only use sinking cards therefore all our I/O is PNP or sourcing devices.
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
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- Retired
On OUTPUT modules, I describe it as whether the module switches the common (sink) or the hot (source).
If you are pretty good with electronics, a sink output is (was?) an "open collector NPN" connection, an efficient and low cost system. Sourcing usually involved more costly and SLIGHTLY less efficient (I don't know why) PNP devices ... often controlled by that NPN anyway.
You've some good answers on INPUT modules; I have to review documentation every time to be sure I misunderstand correctly <g>.
james_mcquade
Senior Member
A word of caution, as far as i know Allen Bradley is the only manufacturer that tells you what the input card does. For example, a 1746-ib16 is a sinking card meaning that is sinks the power to ground.
there are other plc's out there that gives you a card number and sinking. This means that the field device must sink power to ground.
i ran into that years ago.
you must always check before buying for the project.
regards,
james
there are other plc's out there that gives you a card number and sinking. This means that the field device must sink power to ground.
i ran into that years ago.
you must always check before buying for the project.
regards,
james
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