Hi all

to identify wire break & short circuit we need serial & shunt circuit resistance for contact inputs.

but I would like is it mandatory that these resistances at field side only??

My instruments does not have them, can I place these resistances at Cabinet side. and monitor LB/SC error.

please share your view.

SUN

 

Hi Sun

>to identify wire break & short circuit we need serial & shunt circuit resistance for contact inputs.

OK you will have a monitored input to detect OC (open circuit) SC (short circuit) and open/closed state of your switch.

If you place the resistors (Rp and Rs) near or inside your cabinet: the purpose of these resistors is to detect OC and OP; if your resistors are connected inside the junction block of the cabinet of your technical room, the system will not be able to detect a difference between OC and open position (the same with SC and closed position) between the device and the cabinet. In this case, please just imagine that you will receive 2 wires in the cabinet (without resistors on field) from your switch so how to detect several level of voltage (you need 4 levels of voltage for open/close/OC/SC state)?

When we specify that we need monitored input (for manual call point in F&G for example), we ask to add these resistors inside the device (and sometimes, it is a vendor option, we just have to define the values of the resistors Rp and Rs according to the PLC).
Note that it is not easy to connect the serial resistor inside your device if you don't have spare/free connections...no problem for the parallel resistor!

regards

 

Hi Sun

If you want, give me your email address and I can send you a drawing to clarify my explanation.

regards
Bruno

 

please send me drawing as well on [email protected]...thanks in advance

Regards
Gurpreet

 

> please send me drawing as well on [email protected]...thanks in advance

See links below for good info on this. (Called resistive coupling.)
http://www.bartec.de/ProdCatalogue/Assets/Datasheets/lng_0/C281178_E.pdf

http://www.wago.com/wagoweb/documentation/288/eng_dat/d893600e.pdf

Carl D