On the 4100/6100/8100 series controllers the 4-20mA input shuts off its output and displays "OPEN" on the display if the wires for the input are broken. The controller goes to this state when ever the input signal current falls below approximately 0.5 mA.
Between 0.5mA and 4mA underange is indicated on the display with the [LL] display. During underage condition outputs will continue to be active.
