Instrument Wiring Confusion with PLC IO Card

[obi1987]

I always have confusion about Instrument wiring. I have to clear my concepts about so I am confident at site.
What things I should know or I considered before wiring.
For Example start with PT,TT.
There are two types as I know 2 Wire and Three Wire.
2 Wire Which are not required Power and Just wire the positive(signal) to the Analog Input Point.
3 Wire which are required power so I wire the Positive to the Analog input bit and Negative with the + of 24v DC?

Detail I mentioned above is my understanding.Some Detail Information and discussion is appreciated.

Thanks

 

[Bit_Bucket_07]

I always have confusion about Instrument wiring. I have to clear my concepts about so I am confident at site.
What things I should know or I considered before wiring.
For Example start with PT,TT.
There are two types as I know 2 Wire and Three Wire.
2 Wire Which are not required Power and Just wire the positive(signal) to the Analog Input Point.
3 Wire which are required power so I wire the Positive to the Analog input bit and Negative with the + of 24v DC?

Detail I mentioned above is my understanding.Some Detail Information and discussion is appreciated.

Thanks

You are incorrect in your assumptions.

A "two wire" instrument does not provide the excitation power for it's output, regardless of whether the instrument requires an outside power source in order to operate. A "three wire" or "four wire" instrument does provide excitation power for it's output from the same source that powers the instrument.

For a two-wire, 4-20mA instrument you would connect PS+ to the + terminal of the instrument, connect the - terminal of the instrument to the + terminal of the Analog Input, and connect the - terminal of the Analog Input to the PS-. You are simply wiring a basic series circuit.

For a three wire instrument, you would connect the + terminal of the instrument to the + terminal of the Analog Input, and connect the - terminal of the instrument to the - terminal of the Analog Input.

 

[Mickey]

Does this help?

 

[obi1987]

Thanks both of you.Both things are helpful for me.