Reading free potential contact

[Jelf]

Hello,

I'd like to measure is a free potential contact on/off with a datalogger.

Can I do as described in an attached pdf-file?

Thanks for help!

 

[Amr Hassan]

i think u have to connect the common of supply and data logger

 

[JesperMP]

Hello Jelf.

Is the problem, that the datalogger has another input voltage than the 24V that you have available (10V for example) ?
If so, then yes you can connect it via a voltage splitter like you suggest.

And yes, you also have to connect the common.

 

[Jelf]

Thanks for answers.

I'm using this same +24 V DC as a power supply for datalogger, so I planned to use this to feed measuring circuit.

Is there normally some limits regarding maximum voltage and/or current that can be fed through potential free connection?

If needed I can reduce voltage to connection to PLC with for example voltage splitter. And same with current if there is maximum current through potential free connection.

Hello Jelf.

Is the problem, that the datalogger has another input voltage than the 24V that you have available (10V for example) ?
If so, then yes you can connect it via a voltage splitter like you suggest.

And yes, you also have to connect the common.

 

[Amr Hassan]

u have to check the rating of contact (see the data sheet of the plc) for siemens i guess it is 2A

Normally if u have input to a data logger , the current is usuualy very small

 

[JesperMP]

I'm using this same +24 V DC as a power supply for datalogger, so I planned to use this to feed measuring circuit.

That in it self does not mean that the input channel of the datalogger is tied in with the same common. As I dont know your datalogger, it may have an isolated input.

Is there normally some limits regarding maximum voltage and/or current that can be fed through potential free connection?

Of course. However, 24VDC and an input with high input impedance should be no problem.

If needed I can reduce voltage to connection to PLC with for example voltage splitter. And same with current if there is maximum current through potential free connection.

What exactly is it that you want to do ?
I sense some confusion here.

What voltage is the input on the datalogger ?

 

[Jelf]

Hello Jesper,

I know my datalogger, and that's the way it should be powered and measured. So no problem with the use of datalogger.

PLC's free potential contact closes, if motor's spesified RPM is achieved. I just want to record this information for couple of weeks with datalogger. To get this information I planned to feed circuit with voltage, reduce current to say 10 mA and measure voltage over resistor with datalogger.

I hope that answered to your question.

If I understood correctly, that shouldn't be problem?

That in it self does not mean that the input channel of the datalogger is tied in with the same common. As I dont know your datalogger, it may have an isolated input.

Of course. However, 24VDC and an input with high input impedance should be no problem.


What exactly is it that you want to do ?
I sense some confusion here.

What voltage is the input on the datalogger ?

 

[rPraveenkum]

so you want to log the Motor RPM once it reaches its full rpm thats your application & requirement?

 

[Jelf]

In prinpicle yes. I also have more sensors connected to datalogger, but that won't affect measuring free potential connection.

so you want to log the Motor RPM once it reaches its full rpm thats your application & requirement?

 

[rPraveenkum]

For that you have not shown any rpm transducer in your inital Post?

 

[JesperMP]

To get this information I planned to feed circuit with voltage, reduce current to say 10 mA and measure voltage over resistor with datalogger.

Unless you state some information that clarifies why you want to "reduce current" and "measure over resistor" then I cannot say if "that shouldn't be problem".

Like said before:

What voltage is the input on the datalogger ?

 

[rsdoran]

Hello Jesper,

I know my datalogger, and that's the way it should be powered and measured. So no problem with the use of datalogger.

PLC's free potential contact closes, if motor's spesified RPM is achieved. I just want to record this information for couple of weeks with datalogger. To get this information I planned to feed circuit with voltage, reduce current to say 10 mA and measure voltage over resistor with datalogger.

I hope that answered to your question.

If I understood correctly, that shouldn't be problem?

Undoubtedly you do not know something about the datalogger or you would not be asking this question.

The point,that is trying to be given, s that regardless of how you wire the voltage/current value through the relay contact if the datalogger is not wired with the source voltage common then it will not read it.

IF the datalogger is powered with the same 24vdc source then why do you need to limit voltage/current.

So far you are stating you know the equipment, you know the wiring is correct, but asking us if it will work. How would we know? You will not answer the questions asked.

 

[Jelf]

I think I have put set up my question badly and in a misleading way...

Regarding to wiring drawing of datalogger, I'm of course measuring voltage compared to common. Way I did draw it, was just different. As I have learned, empty circle when talking about voltage means "compared to common". I attached new file, with clarified wiring, so now there is two wires connected to datalogger...

Undoubtedly you do not know something about the datalogger or you would not be asking this question.

The point,that is trying to be given, s that regardless of how you wire the voltage/current value through the relay contact if the datalogger is not wired with the source voltage common then it will not read it.

IF the datalogger is powered with the same 24vdc source then why do you need to limit voltage/current.

So far you are stating you know the equipment, you know the wiring is correct, but asking us if it will work. How would we know? You will not answer the questions asked.

IF the datalogger is powered with the same 24vdc source then why do you need to limit voltage/current.

Reason for this can be found in my previous messages

Is there normally some limits regarding maximum voltage and/or current that can be fed through potential free connection?

 

[JesperMP]

I wonder how many posts this will take.

Like said before:

Like said before:

What voltage is the input on the datalogger ?

(This is my final attempt)

 

[Jelf]

I don't get your point. How does it affect to PLC what is the input voltage of datalogger?

But answer to your question. If I use for example 1000 ohm (first resistor) & 100 ohm (second resistor) resistor, Vin 24 V , so voltage to datalogger would be 2,18 volts when switch is closed.

Datalogger's range is 0-10 V.

Or did I misunderstood your question?

What voltage is the input on the datalogger ?

Like said before:
(This is my final attempt)