Sensor Wiring question

Join Date
Aug 2010
Location
Missouri
Posts
16
I'm sure this is a common sense question but I have to ask since I've never wired a PLC.

I have a sensor with two wires. My PLC terminal has one wire. Am I correct in assuming that the + wire from the sensor goes to the PLC terminal and the - wire is connected to the common from the power supply to the PLC?

Thanks in advance.
 
If we only knew what sort of sensor you're talking about and what sort of input card you want to connect it to...

Without this info you might be given totally opposite answers.
 
suppose its a 24vdc sensor and you have a 24vdc input card then you should wire + to the sensor then the other sensor part to the input. It should say in the manual wich part is wich
 
ok since I'm not the expert i asked my client what they have. Here is what I know.

1. Panasonic FP-X PLC.
2. 24vdc relay which has a positive and negative wire running to the PLC.


The PLC has one screw for the relay wire. If I put the positive wire from the relay to this terminal then the question is where do I put the negative?
 
OK, have you ever heard the saying 'A little knowledge is a dangerous thing'. That is where you are now. You need to get help from someone at your firm to guide you. The reason I say this is that a sensor is an input device, a relay is not a sensor, a relay can be either an input or an output device. You need to learn the basics and you need to have someone at your firm who can help you, otherwise any project you do will go wrong and will cost a lot to put right. Please, please, find a college course on basic electrics.

Bryan
 
LOL ok.

OK, have you ever heard the saying 'A little knowledge is a dangerous thing'. That is where you are now. You need to get help from someone at your firm to guide you. The reason I say this is that a sensor is an input device, a relay is not a sensor, a relay can be either an input or an output device. You need to learn the basics and you need to have someone at your firm who can help you, otherwise any project you do will go wrong and will cost a lot to put right. Please, please, find a college course on basic electrics.

Bryan
 
Section 5 of the FPX manual has the wiring examples. I would grab the manual and give it a thorough read.
That way if you still have questions you can be more specific!
 
Ok I haven't been able to get a perfect answer from anyone so here it goes.


This first photo shows the panel that contains the wires (this is the hardware we are phasing out). On line 17 there is a white wire and a blue wire. I've put voltage meter on the wires and I see the cycles:

22 Second of appx 20vdc
6 Secons of 0 volts.

This is what I expect coming from the machinery.
979919762_Da6mx-M.jpg




Here is the Panasonic PLC I have. We have terminals X0-X6 and one port that says COM.
979919863_8dhMY-M.jpg


I'm unsure if I need to place the white or the blue wire to the COM. I'm sure this is a common sense question to many of you. I'm just new to this whole PLC thing.


Any Ideas?
 
Typically COM stands for Common. I would check the electrical diagrams of the existing system to clarify which wire is which and then check
Section 5-17 of the manual(ARCT1F409E-3.pdf). It has the diagrams of the wiring examples along w/ the specific instructions this PLC requires/recommends.
 
I would not go by color as different companies have different color representations. Com is your common port which can also be electrically defined as a ground port. your negative of the sensor will go here. I see there are 8 inputs X0-X8. The positive of the sensor goes here. If your sensor will receive any data from the PLC such as programmable sensors, then it will go to Output side of the PLC. Usually a connection to COM completes the circuit.

Since its only a 24 VDC source, I wont be too worried of blowing up the circuit and try this out !
 
Well, how sure are you of the input (or I guess, the output from the machine) type? Draw us a diagram showing how the existing setup operates including the 24VDC power supply.

I ran into a sinking output once.. ding it.
 
I'm suspicious of the wiring at the second picture. It shows a power cord connected to the power terminals (Line and Neutral) of the power supply. The brown wire which is on the N (neutral) terminal is usually connected to the hot blade on the plug and the blue wire which is on the L (line) of the power supply is usually connected to the neutral blade. So I think your power supply is wired backwards. In other words, the neutral terminal is probobly hot. Watch out!
 
Here's the thing. You haven't provided enough information to answer your question. In DC controls there are two types of wiring. You can use the 0VDC side as the common and then all the control signals are 24VDC or you can use the 24VDC side as common and use the 0VDC for the control signals.

The 0 Common is more prevalent in the western hemisphere and the 24V common is popular in Asia. (There are entire threads on which is better but that is besides the point for you). Generally you have only one of these methods on a machine. Now, with the double terminals on your original system, there may have been the possibility to mix and match since each input seems to have two connections. But we don't know that and apparently neither do you? You can read about these two methods of wiring inputs here: http://www.patchn.com/index.php?option=com_content&task=view&id=57&Itemid=36

We tend not to like people getting shocked or hurting themselves or others and the lack of information here doesn't help with that.

Your best bet for specific help is to provide a diagram of how things are wired now including part numbers and manufacturers of items and if possible links to the manufacturers data sheets.
 
I was very concerned (over-statement, really!) when I saw you were an integrator, assuming systems integrator, asking this question... until I found you work as an LED Sign Integrator.

What info have you got on the component board where terminal bank 17 is?

With respect to the relevant 0v common reference what voltage do you measure on the blue and white wires you question?

Is the power cord to the Panasonic PLC of correct polarity?

At the bottom rail of the PLC is there a 24vdc source-out?

Until I have downloaded the manual I don't know. http://panasonic-denko.co.jp/ac/e/fasys/plc/plc/fp-x/manual/index.jsp

Help us help u

.
 
Last edited:

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