What are the pull up resistors on the universal inputs used for?
Information on the pull up resistors selection switch.
The pull up resistors on the inputs are used to configure the input impedance, for example on the 810 series i2/b3 field controllers the input impedance can be 30.1K ohms referenced to 10.000 V or 10 M ohms referenced to ground with the input reference resistor switch set to OUT
Pull up resistors are configured via the DIP switch located in the general area of the inputs, each small switch corresponds to the input with the same number.
If an input is either a thermistor or a digital input, switch its input reference resistor switch to IN. (switch ON) If you require that the input be high impedance (10 M ohms), set its input reference resistor switch to OUT. (switch OFF)