Allen Bradley 1756-IF8 ControlLogix Analog Input Module

The Allen Bradley 1756-IF8 is an analog input module from the ControlLogix Programmable Automation Controller (PAC) family. This analog input module features Eight (8) input channels that are configurable for a variety of input signals such as +/-10VDC, 0-10VDC and 0-5VDC Voltage signals and 0-20 mA Current signals.

This module is typically used to interface analog signal generating instruments and devices such as transmitters, transducers, signal splitters, signal isolators, panel meters and other similarly capable devices.

The 1756-IF8 is a single slot module with a high-resolution of conversion. It has varying resolution, from 15-bit to 16-bit. Specific module resolution is ±10.25V: 320 µV/count (15 bits plus sign bipolar) for +/-10VDC, 160 µV/count (16 bits); for 0-10VDC, 80 µ/V count (16 bits); for 0-5VDC and 0…20.5mA: 0.32 µA/count (16 bits) for 0-20 mA signals.

There is virtually no limit to the number of installation instances of this module. Most ControlLogix controllers are capable of up to 4000 analog I/O signals. The 1756-IF8 may be installed in the local chassis along the controller or within distributed I/O racks.

The 1756-IF8 used the Sigma-Delta conversion method and saves received signal in Integer mode (left justified, 2 s complement) IEEE 32-bit floating point register. It uses 1756-TBCH and 1756-TBSH removable terminal block (RTB) with user defined, mechanical keying.

The module scan time also varies depending on the wiring configuration. For single eneded wiring, scan time is 16-488 ms, for 4 point differential, scan time is 8-244 ms while 5-122 ms for 2 point differential inputs.

The 1756-IF8 can be wired in three different ways: single-ended wiring, differential wiring, and high-speed mode differential wiring. In single-ended wiring, all the input devices are tied to a common ground and it allows the comparison of one side of the signal input to the signal ground. The difference is then used by the module in generating digital data for the controller. Using the single-ended wiring method maximizes the number of the module’s usable channels. You should use differential wiring when your applications can have separate signal pairs or common ground is unavailable and when you need improved noise immunity in your environment. Channels in this wiring method are not totally isolated from each other. But when you need the fastest data updates possible, you should use the high-speed mode differential wiring method. Note that this mode only allows the use of one out of every four channels on the module. Specific features of the 1756-IF8 include the module filter, under-range/over-range detection, process alarms, wire off detection, multiple input ranges, real-time sampling, digital filter, and rate alarms. Its backplane voltage and current ratings are 5.1 Volts DC, 150 milliamps maximum, 24 Volts DC, and 40 milliamps maximum. It has an input current range of 4 to 20 milliamps and an input voltage range of -10 to 10 Volts. Power consumption is 1.73 Watts and the maximum overvoltage protection is 30 Volts DC (voltage) and 8 Volts DC (current).

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Specification Sheet .pdf