The Allen-Bradley 1756-OB8 is a ControlLogix discrete output module. This module delivers an ouput voltage range of 10-30 VDC with nominal value of 24VDC. It is used to energize electrical loads that operate in DC voltages as well as AC loads, used with an interposing circuitry.

The 1756-OB8 is a single slot module that occupies any available slot of the chassis except the left-most slot which is intended for the ControlLogix processor or ControlLogix communication adapter / scanner module. It is compatible acting as a local I/O component or as part of a distributed I/O system. It may be installed to any available 1756- ControlLogix chassis and operate along standard or power supply modules.

The 1756-OB8 has a backplane current draw of 165 mA at 5.1 VDC and 2 mA at 24VDC while the total backplane power is 0.89 W and power dissipation of 2.5 W @ 60 °C (140 °F) and thermal dissipation of 8.53 BTU/hr. Each channel of this output module can deliver up to 2 Amperes @ 60 °C (140 °F) and 8 Amperes @ 60 °C (140 °F) per module.

This module uses a Removable Terminal Block (RTB) for connecting each channel of the module to the electrical loads. Compatible RTBs are 1756-TBNH and 1756-TBSH while appropriate RTB keying is user-defined, mechanical keying.

It is entered in the hardware configuration where module parameters and properties can be further modified/ Some of these parameters are Request Packet Interval (RPI), filter time, module inhibition and many others.

This module uses a Removable Terminal Block (RTB) which can either be the 1756-TBNH or the 1756-TBSH (20 pins RTB). This module has the following communication formats available: rack optimization, listen-only - rack optimization, output data, listen-only output data, and scheduled output data. Pilot duty is also available for the 1756-OB8 module.

The 1756-OB8 module has a voltage category of 12/24 volts DC source and an operating range of 10 to 30 volts DC. Its current draw is 165 mA at 5.1V and 2 mA at 24V. It has a backplane power of 0.89 W, with a maximum dissipation of 2.5 W at 60 Degrees Celsius (140 degrees Fahrenheit), and a thermal dissipation of 8.53 BTU/hr. The maximum off-state leakage current of this module is 1 mA per point and during an on-state, it has a maximum voltage drop of 1.2V DC at 2 A. It also has a maximum current of 2 A per point at 60 Degrees Celsius and a maximum current of 8 A at 60 Degrees Celsius per module. Its surge current per point is 4 A for 10 ms each that is repeatable every 1 s at 60 Degrees Celsius and its minimum load current is 2 mA per point. The module's isolation voltage is continuous at 250V. This module also allows you to modify states in Fault Mode per point and states in Program Mode per point. The choices for both are Hold Last State, On, or Off, with 'Off' set as default. Temperature ranges for the 1756-OB8 module are 0 to 60 Degrees Celsius when in operation and -40 to 85 Degrees Celsius when not in operation. It also has a maximum surrounding air temperature of 60 Degrees Celsius and a non-condensing relative humidity of 5% to 95%.