What is Loop Checking?

The Loop checking is defined as pre-Commissioning activity which is initiated after installation of instruments at x location to y location instruments or systems.

Loop checking is basically done to ensure the instruments installed at x and y location has continuity signal with each other potential’s.

Loop Checking

If we want to loop check the continuity from instrument to junction box this is achieved by laying a cable between instrument and junction box.

Normally after installation and cable laying during construction activity is to be ensured that instrument and cable and junction terminals and cable which is layed underground or above ground & is not damaged to confirm this damage it is mandatory to carry out loop checking between instruments-junction box- DCS that is from field to control room.

Simple Process:- is short the two cores of cable at one end and check with digital multi-meter at other end if the circuit resistance is ok then the same cores have the cont unity which means that the cable cores are’nt damaged. above procedure also helps to identify the particular cable cores for specific system function

Above process is called as Cold Loop Checking loop checking without any external source simulation.hence called as cold loop check


Loop check activity is checking entire loop functionality, from field to DCS or ESD or PLC or any logical system. It is necesary to check not only continuity of signal, but also range of calibration, alarms, set points and any signal included in the loop folder.

For DCS will be tested with hart comunicator or temperature generator, 4-20mA, depends of witch instrument is involved.

For ESD (emergency shut down system) loop check will be done with proper instrumentation tools to produce the specific presure or requaired level…

For valves you must check all signals as open, close, hi and low limit switch, reset buttons, hand switches , feedback must be check and a lot of other things must be checked .

Loops are direct, revers, split range … it is not easy and it is not only the continuity check to do.