Do I need to add pull-up or pull-down resistors to my Sealevel inputs?
No. Sealevel optically isolated and dry contact inputs are current-mode inputs, which do not require external pull-up (or pull-down) resistors to be added for most applications.1
External pull-up (or pull-down) resistors are generally required on voltage-mode inputs found on cheaper, non-isolated input devices. Voltage mode inputs require pull-up (or pull-down) resistors to hold the inputs to a known state when not driven by or connected to an output signal.
Sealevel optically isolated and dry contact inputs use an enhanced current-mode input design and are inherently EMI resistant. This means they are immune to false triggering caused by electrical noise that is commonly radiated into the field wiring by nearby motors and other industrial equipment.The superior circuit design of Sealevel inputs simplifies the process of field wiring the device, while improving signal integrity and reliability.
1Note: Open-collector or open-drain outputs connected directly to the inputs may leave the connection floating. Adding pull-up (or pull-down) resistors will maintain a known voltage on the connection when not driven.