General Information

Core Description

Engineered for reliable industrial loop execution, the 1794-OF4I is an Allen-Bradley FLEX I/O isolated analog output module featuring 4 independently isolated channels with a high-precision 15 bits plus sign resolution. Operating on a nominal 24V DC field supply with a 19.2 to 31.2V DC range, this open-style module converts digital commands using an internal digital-to-analog converter with a rapid step response of under 25 µs. Each channel is fully opto-electrically separated to prevent hazardous ground loop feedback, ensuring continuous signal accuracy drift stays within 0.0012% per °C for voltage and 0.0025% per °C for current loops across dense industrial automation grids.

Specific Application

• Isolated Multi-Range Actuator Control: Driving mixed field-level proportional control valves, dampers, and speed drives across varying voltage or current loops without external signal splitters.
• Hazardous Area Signal Isolation: Deploying isolated analog loops inside classified Zone 2 / Class I Division 2 industrial environments requiring strict T4A temperature code ratings.

Ordering Information

System Compatibility

• System Compatibility: The 1794-OF4I module mounts exclusively onto 1794 terminal base units, requiring its physical keyswitch to be rotated strictly clockwise to Position 4 before insertion. It draws a backplane bus current of 55 mA at 5V DC and demands a maximum external DC supply current of 210 mA at 24V DC. The module fully interfaces with FLEX I/O backplanes via standard communication adapters, supporting 2's complement, 2's complement %, binary, and offset binary data formats.
• Direct Application Alternates: 1794-OF4D (FLEX I/O Diagnostics Analog Output Module) and 1794-OF8IH (FLEX I/O XT High-Density Isolated HART Analog Output Module).
• Key Differences from Alternates (1794-OF4I vs. OF4D / OF8IH):
• Galvanic Isolation vs. Diagnostics: While the 1794-OF4D features electron-switch diagnostics to monitor active line faults across non-isolated paths, it lacks point-to-point protection. The 1794-OF4I provides heavy galvanic isolation certified at 120V continuous basic insulation for standard bases and up to 250V continuous basic insulation when paired with a NEMA-style base, allowing channels to cross completely independent power references.
• HART Protocol & Environmental Resiliency: The next-generation 1794-OF8IH introduces onboard HART digital communication pass-through and doubling the channel density. Additionally, as part of the FLEX I/O-XT line, it handles wider temperature extremes than the 1794-OF4I's standard operating envelope of -20 to +55 °C, though the 1794-OF4I remains highly cost-effective for pure analog loops that do not require digital instrumentation diagnostics.

Installation & Troubleshooting FAQ

Q1: Why will my new 1794-OF4I module not physically seat or lock down into the terminal base unit?

A: This indicates a mechanical alignment or configuration error during mounting. First, verify that the mechanical Keyswitch on your 1794 terminal base is set precisely to Position 4; the module will physically bind if the keyswitch is rotated to any other number. Second, ensure that the slideable Flexbus connector is pushed entirely to the left to link with the neighboring base, as the module chassis features an physical interlock that blocks insertion unless the bus connector is fully extended. Finally, check that the alignment bar on the bottom of the module slots cleanly into the base groove before pressing firmly to engage the latching mechanism.

Q2: The front-panel OK status indicator is flashing green on my 1794-OF4I. What does this flash sequence mean?

A: A bi-colored bi-flashing green indicator points to one of three technical conditions rather than a hardware failure: 1) The module configuration word is currently set to zero (typical during a power-up reset sequence before the PLC downloads parameters), 2) The 24V DC external user power supply is turned off or disconnected, or 3) The module is currently locked in configuration mode. If the indicator transitions to solid or flashing red, it means the unit failed its internal hardware boot test and you must cycle power to attempt a proper interface reset.

Q3: What critical wiring constraint must be followed regarding multiple loops on a single 1794-OF4I channel?

A: You must connect only one current or one voltage signal per channel. The terminal base architecture shares internal conditioning components per channel path; attempting to land both a current feedback loop and a voltage command line on the exact same channel will corrupt the digital-to-analog converter metrics, skew the absolute accuracy beyond its 0.1% full-scale specification, and potentially trip a bad calibration (BD) error flag in your software input map.

Q4: How do I select and wire the right terminal base to achieve a higher 250V continuous isolation rating for the 1794-OF4I?

A: Your isolation threshold depends strictly on the model of terminal base unit deployed in the cabinet. If you mount the 1794-OF4I onto standard 1794-TB2, 1794-TB3, 1794-TB3S, 1794-TB3T, or 1794-TB3TS bases, the continuous isolation is limited to 120V. To achieve the maximum certified 250V continuous isolation rating across channel-to-channel, channel-to-user, and channel-to-system loops, you must install the module exclusively onto a NEMA-style 1794-TBN terminal base, routing your signal lines using shielded Belden 8761 cables.

Q5: What are the electrical arc risks and structural rules when adjusting the 1794-OF4I in explosive atmospheres?

A: The 1794-OF4I features an open-style enclosure rating certified for UKEX/ATEX/IECEx Zone 2 (Ex ec IIC T4 Gc) locations. Because removing or inserting the module or adjusting field wiring while power is applied can trigger an electric arc, you must ensure that all power has been completely isolated or the area is verified as nonhazardous before hot-swapping or disconnecting lines to avoid explosion hazards. Additionally, the unit must sit inside a tool-accessible cabinet rated to at least IP54 with a nonmetallic flame spread rating of 5VA, grounded through a passivated steel DIN rail secured every 200 mm.

Certification

• Australian RCM
• China CCC
• Registro Italiano Navale
• American Bureau of Shippin
• CE
• CSA Listed
• ATEX
• CSA Listed Hazardous
• Korean KC
• IECEx Scheme
• Eurasion Economic Community
• Safety
• UL Listed Hazardous
• UL Listed
• UKCA DOC
• UNITED KINGDOM SAFETY CERTIFICATE
• MOROCCO DOC
• UK EX CERTIFICATE

This product was certified with the above certifications as of {}. Products sold before or after this date might carry different certifications. Please review the product label to check for the certifications your specific product carries.