Description

1797-PS2N2 — FLEX Ex Intrinsic Safety Power Supply

Product Overview

The 1797-PS2N2 is an intrinsic safety power supply from Rockwell Automation, built for the Allen-Bradley FLEX Ex I/O system — the distributed architecture that places control I/O directly inside hazardous areas instead of forcing every signal back to a safe-area marshalling cabinet. The module accepts a 24V DC source from the nonhazardous zone and converts it into four independently energy-limited outputs of 8.5 W each, delivering that power through an explosion-proof enclosure with 1-inch NPT conduit entries to the FLEX Ex modules, valves, actuators, and transmitters installed in the classified location.

Its fundamental job is stated plainly in the official installation instructions: the power supply must isolate the unsafe incoming power from the control system and limit the available energy to IS-safe levels. Every output is galvanically isolated from the source and each channel is independently current-and-voltage limited, so a fault on one field loop cannot propagate back toward the controller or raise the energy available at another loop beyond its certified entity parameters.

For plants operating Division 1 or Zone 1 instrumentation, the practical payoff is a simpler, cheaper architecture. Distributed FLEX Ex I/O eliminates long individual cable runs to safe-area barriers, reduces marshalling, and lets instrument power be sourced exactly where it is used. With dual input feeds for redundancy and a fully sealed, outdoor-rated housing, the 1797-PS2N2 addresses the two problems that dominate hazardous-area power design: energy containment and continuity of supply.

Technical Specifications

参数名称	参数值
Product Model	1797-PS2N2
Manufacturer	Rockwell Automation / Allen-Bradley
Product Type	FLEX Ex intrinsic safety power supply, 24V DC in / quad-Ex DC out
Input Voltage Range	19–32V DC
Input Current	3.1 A, ripple 5% AC
Output Channels	4 channels × 8.5 W, independently IS-limited
Output Voltage / Current	Uo < 9.5V DC; Io < 1 A
IS Entity Parameters	Co (IIC) < 500 nF; Lo (IIC) < 8 μH; max output cable resistance < 0.1 Ω
Isolation	IS outputs galvanically isolated from input (UL 913 / CSA 157)
Enclosure	Explosion-proof, 1 in. NPT conduit entries; IP66 / NEMA 7B
Operating Temperature	-20…+70 °C (storage -40…+85 °C)
Dimensions / Weight	approx. 140 × 174 × 174 mm; 7.3 kg (16 lb)
Certifications	UL/cUL File E197983; FM Certificate 3009806; Class I Div 1 Groups A–D; Zone 1 AEx ib IIC T4

1797-PS2N2

Key Features and Advantages

Quad-channel energy limiting: Each of the four 8.5 W outputs is limited independently, so a short circuit or overload on one channel is contained at that channel without raising energy on the others. This per-channel discipline is what allows multiple field devices to share one supply while each loop still meets its entity-parameter budget.

Galvanic IS isolation: The output stage is galvanically isolated from the 24V input to UL 913 and CSA 157 requirements. Fault energy, transients, and ground anomalies on the input side physically cannot reach the hazardous-area circuits, which is the difference between a certified loop and a compromised one.

Dual-feed redundancy: Two input power feeds are provided for source redundancy, so losing one upstream 24V source does not drop the entire hazardous-area I/O network. For continuous processes this removes a single point of failure that a conventional single-fed barrier rack would carry.

Explosion-proof hardware, not just a barrier: The housing is rated IP66 / NEMA 7B with 1-inch NPT conduit entries, meaning the supply can be mounted outdoors, washdown areas, or directly in the classified zone without a separate protective enclosure — something a standard DIN-rail power supply can never offer.

Rugged environmental ratings: The module operates across -20…+70 °C, survives 15 g shock and 2 g vibration per IEC 60068, and is rated for 5–95% noncondensing humidity, matching the reality of wellheads, compressor decks, and outdoor process skids.

Architecture simplification: By powering FLEX Ex modules at the point of use, the 1797-PS2N2 removes dozens of individual safety barriers and long instrument runs from a typical project, cutting both installed cost and the engineering effort spent on loop energy calculations.

Documented certification path: Entity parameters, wiring methods, and installation rules are published in the official control drawing, giving engineers a traceable basis for hazardous-area approval and inspectors a clear standard to verify against.

Application Areas

In oil and gas production, the 1797-PS2N2 powers FLEX Ex I/O at wellheads, separator skids, and tank farms, where transmitters, valves, and actuators sit in Class I Division 1 or Zone 1 areas and a power failure directly halts production. The same supply serves refinery and petrochemical units, where ControlNet-connected I/O racks must run continuously in classified zones without the cost of conventional barrier marshalling.

Chemical plants use it to energize HART analog and NAMUR digital modules inside process buildings, where solvent atmospheres demand certified energy limits on every conductor. Power generation and utilities deploy it in fuel-handling and hydrogen or gas processing areas, where an arc inside an enclosure is not an acceptable risk. Offshore platforms and marine installations rely on the sealed IP66 housing and vibration tolerance when the supply is mounted on process modules exposed to weather and mechanical stress.

In every configuration the 1797-PS2N2 performs the same role: it is the certified boundary where safe-area energy becomes intrinsically safe energy, and the continuity of that boundary determines whether the hazardous-area network runs for years or fails on the first fault. Typical companion modules it feeds include ControlNet adapters and bus interface units, analog input modules, and NAMUR input modules within the same FLEX Ex system.

Installation and Maintenance

Installation preparation: Before mounting the 1797-PS2N2, verify the entity parameters for the specific revision against the Allen-Bradley control drawing, because the output characteristics changed between the PS2N and PS2N2 generations. Use the pre-tapped 1-inch NPT entries for both hazardous input and IS output conduit; install poured seals at the enclosure entry for FM installations or within 150 mm (6 in.) of the enclosure for UL, and keep hazardous and intrinsically safe wiring physically separated inside the housing. Scrape paint from the back panel at grounding points and use star washers for a solid electrical bond. After de-energizing, wait 15 minutes before opening the cover, and connect IS outputs only to FLEX Ex modules or adapters so the intrinsically safe backplane integrity is maintained.

Maintenance advice: This module is not field-repairable — any attempt to open it voids the warranty and the IS certification, so failed units must be returned to the factory. Build the inspection routine around the things that can legitimately be checked in the field: conduit seal integrity, lid set-screw tightness, and output cable resistance, which must stay below 0.1 Ω per the specifications. Observe electrostatic precautions around the unit and keep a spare 1797-PS2N2 at the site so a failed supply can be replaced in minutes rather than shutting down the hazardous-area network for the duration of a factory turnaround.

Product Warranty

The 1797-PS2N2 is covered by the standard Rockwell Automation one-year warranty, and every unit ships with the certification documentation trail that hazardous-area inspectors require — UL File E197983 and FM Certificate 3009806, together with the entity-parameter data for the installed revision. Suppliers serving the installed FLEX Ex base offer both new and tested surplus stock, pre-shipment verification of input/output characteristics, and application support for sizing and replacement decisions. Because the IS certification is tied to the exact module revision, the supply chain can match the delivered unit to the plant’s control drawing, ensuring that replacements keep the same energy limits the original approval was based on, with support available for as long as the classified-area installation remains in service.