The Allen-Bradley 1756-IF16H is an analog input module from the 1756 ControlLogix Programmable Logic Controller Automation (PAC). It supports integration of 0-20 mA or 4-20 mA input signal through hardwiring and Highway Addressable Remote Transducer (HART) communication protocol. This module provides Sixteen (16) differential current signals and One (1) HART modem per channel.

The 1756-IF16H has an integrated Analog to Digital Converter (ADC) using successive approximation method. Analog conversion resolution range is 16-21 bits, allowing more measuring points to be displayed. Converted signal is saved in Integer mode (left justified, 2 s complement) IEEE 32-bit floating point number.

Allen-Bradley recommends use of Single wire connection when terminating signals to the 1756-IF16H. Wire diameter is 0.33…2.1 mm2 (22…14 AWG) solid or stranded shielded copper wire with insulation rating of 105 °C (221 °F) or higher and maximum insulation thickness of 1.2 mm (3/64 in.). Compatible Removable Terminal Block (RTB) for use with the 1756-IF16H are 1756-TBCH and 1756-TBS6H.

The 1756-IF16H has a calibrated accuracy which is better than 0.13% of range on all filters while the module error is 0.3% of range. The module’s input scan time is 11…328 ms that is filter dependent while the module HART scan time is estimated at 1 s if all channels are HART enabled.

The 1756-IF16H allows you to choose which among the three data formats to use: analog only, analog and HART PV, and analog and HART by channel. It is important to select the right data format to use, as it determines which values are included in the Input tag of the module and the features that are available to your application. The Analog Only format only has the analog signal values and the analog status. The Analog and HART PV is recommended when you want the members of your tag to be arranged like the non-HART analog input modules. When you choose this data format, the analog values for all channels are grouped near the end of the tag, making it easy to see all the 16 analog values at once. Two input ranges are available for each channel in the module and these are either from 0 to 20 milliAmps and 4 to 20 milliAmps, with the latter being used by the HART instruments. These ranges designate the minimum and maximum signals that the module can detect. The module also has a module filter that attenuates the input signal beginning at the specified frequency. This is applied on a module-wide basis, affecting all channels. Note that HART instruments should not use the 1000 Hertz module filter. Real-time Sampling (RTS) is also another feature of this module. Applied module-wide, this parameter instructs the module of the frequency of scanning its input channels and obtain all available data. After scanning, the module will then multicast the data. But prior to the module configuration, you need to set the real-time sampling (RTS) period and the requested packet interval (RPI) period. It also has an under-range and over-range detection feature, which allows the module to detect when it is operating beyond the limits of the input range. This is a status indication that will tell you that the input signal is being measured inaccurately, as the signal is beyond the measuring capability of the module. Applied on a per channel basis, the module has a digital filter that smoothens out input data noise transients. Also, the module has a wire-off detection feature, which informs you when a signal wire has been disconnected from one of the channels or if configured for a 4 to 20 milliAmps range, when an RTB is removed from the module.

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