Hi,

We are trying to connect a 3-wire transducer (4-20mA) to the analog input of a CPU313C.
When we measure the output of the transducer, with a multimeter, we get 4mA as 0 value, which is good.
But once we connect the transducer to the analog input card, the value drops to 2.6mA.

We first thought it was a grounding error, but that doesn't seem to be the case.
We have put the transducer and and PLC on a common ground.
The hardware is configured as 4-20mA.
The transducers has a 1000Ohm max load @ 24VDC.

Can anyone help me figure this out?
We have a 2 other (2 and 4wire) transducers connected to this CPU without any problems, the only one giving us trouble is the 3-wired.

Thanks in advance.

Kind regards,
Jens

Good morning!)

Can you post a drawing of how conection been made?

hi Jens,

you should connect your transducer as a 4-wire-transducer. 4-wire-transducer are with a seperate power-supply, which you have with your pins "+" or "L" and "-" or "M". Where your analogue Output-Pin should connected depends on the measuring-device. Maybe you have to connect the M to the device too.   

SIMATIC S7-300 CPU 31xC and CPU 31x: Technical specifications

see the manual on page 279

hope this helps,

regards,

Dear All,

thanks for the replies, check wiring diagram in attachment.
(Sorry for duplicate posts, I have forum bugs using IE, now using firefox)

Kind regards,
Jens

hi Jens,

thats the way it should work.

regards,

mopS04

hi Jens,

thats the way it should work.

regards,

 Hi mopS04,

thanks for the replies. I thought so too, but for some reason whenever I connect the transmitter to the input card, it drops down from 4mA to 2.6mA. I've attached a drawing which shows, what works and what doesn't work. Any ideas what could be wrong?

Thanks in advance.

Kind regards,
Jens

hi Jens,

how are your settings? Is it parametrized as 4-wire-transducer?

reagards,

mopS04

hi Jens,

how are your settings? Is it parametrized as 4-wire-transducer?

reagards,

Hi mopS04,  Yes it is

sory for late answer.

please see attachment