sensor problem

i'm used photo sensor in my project. i've check with multimeter, when it detect the object, the voltage at sensor output is 23.4V. Then when it's not detect, the voltage is 0V. Since PLC(omron) input is 24V. should i make another circuit at the sensor output to make it 24V if i want to connect to PLC unit??

Do you have the correct match for sinking and sourcing?

If not, you're better off getting the correct sensor for your input card then creating voltage driver circuits.

Double message. Sorry.

Looks like your PLC input module has 24VDC. Therefore, you need an interposing relay from your photo sensor to give a dry contact to the PLC input.

Normally, everything over about 17V is considred a "1"-level, everything below about 8V is considered "0"-level.

More important is to know what kind of sensor you use: PNP (sourcing) or NPN (sinking). Make sure the input card is the correct one for the sensor (or the sensor is the correct one for the input card). Check the chapter about DC inputs in the PLC course on this site (click the "Learn PLCs" link on top of this page).

Kind regards,

You do not mention which model PLC you are using. However, generally all Omron inputs are bi-directional with respect to sinking or sourcing - only the common changes.

It appears you have a PNP (+) output from the sensor. The inputs into the PLC will all have to be positive. This means that the common on the input block/card should be negative. The sensor then should work satisfactorily into the PLC. Also make sure the sensor power supply is fed from the same power supply you use for the common to the input block/card.

cikoi...??? Are you there??? Hello, cikoi... Where are you???

There might be a mis-understanding in concept... at least as described...

Input devices are connected to INPUT Terminals... NOT Output Terminals.

Additionally, as indicated previously, you need to know the difference between Sourcing and Sinking.

A "PNP" Sensor is a Sourcing device. The Input Terminal must be Sinking (NPN).

An "NPN" Sensor is a Sinking device. The Input Terminal must be Sourcing (PNP).

Hello... cikoi... are you there?

PLC.net calling cikoi.... are you there cikoi?

yeahh..i'm here..

Terry Woods said:

A "PNP" Sensor is a Sourcing device. The Input Terminal must be Sinking (NPN).

An "NPN" Sensor is a Sinking device. The Input Terminal must be Sourcing (PNP).

Click to expand...

I disagree. Granted, the Input card should be 'sink', but it will still be a PNP card?

Don't let this thread turn into one of those mammoth PNP/NPN Sinking/Sourcing debates.

As BobB says, Omron inputs can be wired either way.

@cikoi
If I understand your original question, 23.4v will be ok with a 24v input card.

Pp

no need u can use with 23.4 voltage. it will!

1) In Omron speak (and many other brands) a negative common on the input card means a positive input from a PNP output device will turn the input on - 23.4 VDC is well within the capabilities of the input card. A positive common on the input card means a near zero input from an NPN output device will turn the input on.

2) Alan Bradley appear to differ in the way they describe NPN and PNP. They totally confused me the first time I had to use an AB PLC - that was after using Omron, Mitsubishi, Hitachi, Siemens, Texas Instruments, GE-Fanuc and several others by the way. Had absolutely no problem with the way any of them described the function of their input cards.

3) A PNP input device (switches positive) feeds into an NPN input card (negative common) in Omron (and many others) speak. An NPN input device (switches to near zero) feeds into a PNP input card (positive common).

4) It does not really matter how the manufacturer describes the input card - the only thing that matters is that a device that switches high must feed to an input card with a negative common and a device that switches low must feed into an input card with a positive common. At the end of the day the only thing that really matters is that there is a voltage differential (within manufacturers prescribed bounds) that will turn the input on.

5) If one puts a postive switching input device into an input card with a positive common, there is no differential and the input will not turn on. The same holds for a negative switching device to a negative common - nothing happens.

6) I would suggest that anyone new to PLCs only looks at the inputs in this way and there should be absolutely no confusion at all. Forget about the manufacturers "blurb" and invariably unhelpfull manuals and just consider that there has to be a voltage differential to turn the input on.

Don't let this thread turn into one of those mammoth PNP/NPN Sinking/Sourcing debates.

Click to expand...

Absolutely agree!!! Keep it simple as per point 4). Cannot make it much more simple than that no matter how the manufacturers want to carry on with their own descriptions of NPN and PNP inputs and outputs!!!!

THE ONLY THING THAT MATTERS IS VOLTAGE DIFFERENTIAL!!!!!