On/Off Switch to turn on light

[DrNickburns 0]

I am new to PLCs, but my first project is a switch that is plugged into AD1V (analog) and it sends a command to close Y1. This is an automation direct CLICK PLC, and i'm using the Click software. The Y1 led indicator comes on, but I'm confused about where the light would get its voltage. I have a 24 VDC light that has two wires + and -. Where do they actually get wired to the PLC? And where does the 24 VDC come from to power the light? Confused!

[b_carlton 61]

The outputs do not 'create' the voltage that appears on their terminals, they just switch the power present at their 'common' terminal.. Notice the 'C2' terminal just above the set of outputs Y1 through Y4. Internal to the Click are four relay contacts (the outputs). Like any contact they connect power from one side to the other. All four of these contacts have one side connected to C2. The other side of the contacts go to Y1 through Y4 respectively. So you will need some source of power. For just one light the 24VDC power supply you are using to power the Click may be sufficient. In industrial usage though it is normal to have a totally separate power supply. (Especially if you are trying to duplicate the video you inquired about in the Allen Bradley section of the forum.) Your 24VDC power supply has +24 and 0 volt terminals. Besides powering the Click also connect the +24VDC to C2. Connect the +24VDC lead from the light to Y1. Connect the minus lead of the light to the 0 volts terminal of the power supply. Now run your program. Edited 13 Nov 2010 by b_carlton

[DrNickburns 0]

WORKED! Now that I understand the wiring, I took it a step further and connected a temperature transmitter and have it turning on a green light when the temp is below 75, and a red light when the temp is above 75. Piece of cake! I bought two of (these sensors and a water pump that runs on 24vdc to continue on that other project. I understand that the capacitive sensors are digital, and I'll need to learn how to work with digital inputs next!

[b_carlton 61]

The inputs, like the outputs, have a common terminal. One of the leads from your 24VDC power supply will go there. Because you have chosen NPN sensors the POSITIVE lead from the power supply will hook to the common of the inputs. This also means that any other inputs which use this same common will also have to be NPN. Your sensors have three leads. The Brown wire will connect to the +24VDC from your power supply. The Blue will connect to the OVDC side of your power supply. The Black lead will connect to the input terminal. The top diagram on page 3-27 of the Click manual illustrates this hookup, but don't get confused. It is not showing the third hookup (the Brown wire to +24VDC) required by your sensor to operate. The whole NPN/PNP discussion is a whole other topic.

[Leitmotif 0]

Now that you are progessing and getting into newer and bigger you have to watch out for current demand by load to avoid burning out you PLC power supply. The pump may do just that. It is time to learn about interposing relay where PLC output energizes a relay coil and the relay contracts energize the pump motor from a separate power supply. Also you may as well learn about the collapsing field of the relay and install MOV (metal oxide resistor) or a diode across relay coil that conducts to reduce collapsing field voltage. Dan Bentler

[DrNickburns 0]

Someone else mentioned that usually the PLC should be powered by its own power supply; and all other components, e.g. lights, pumps etc are powered by a separate supply. Makes sense.. by the way this is the pump I got. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290420390091&ssPageName=STRK:MEWNX:IT#ht_4714wt_1139

[DrNickburns 0]

Here's my first project! thanks for the help guys

[JRoss 84]

Looks good! Now you can install it on your pool to keep the level right!