Introduction to the SLC-500 Digital Input Module
The SLC-500 Digital Input module detects the status of field devices which are either on or off. This is any type of switch. For example: float switches, pressure switches, push buttons, and selector switches are digital input devices. The auxiliary contacts of a motor starter is another example, however, the coil of a motor starter would be an output.
Think of inputs as “Status”. When an output module calls for a motor starter to engage, the auxiliary contacts will energize an input terminal. The processor has feedback to verify that the motor starter actually did engage.
Types of Digital Input Modules
There are several types of input modules: AC, DC (sinking or sourcing), etc. The most common modules are 16 point modules, however, 8 point, and 32 point modules are also available.
The image above is a 1746-IB16 module. You can think of this module as 16 voltage testers. If you have a 24 volt DC point supply, just attach the common to one of the bottom two terminals. When the + voltage is seen on any of the other terminals, a status light will energize. When the status light energizes, the value of a 1 should be placed into the Input data table in the processor. Then, the program will look at this value to determine any actions that need to be taken. If you have a different type of module, be sure to consult the installation guide for that module.
Replacing the Module
Be sure the battery is not low or missing before you power down the chassis. The SLC-500 does not support removal and insertion under power. Also, for your protection, be sure to shut off field device power. This will be a separate power source. Loosen the two screws on the terminal block. Next, remove the terminal block from the module. On the top and bottom of the module, press in the locking tabs. Be sure you replace the module with the same catalog number. Finally, re-mount the terminal block and power up the chassis.
— Ricky Bryce