Description
The 1797-IE8 is an eight-channel, 16-bit intrinsically safe analog input module from the Allen-Bradley FLEX Ex family. It reads standard 4–20 mA and 0–20 mA two-wire or three-wire transmitter loops and presents them to the controller as engineered units, percent of span or raw integer data — without an external zener barrier or galvanic isolator in the loop.
What sets the 1797-IE8 apart from a plain analog card is the certified energy-limiting front end. The hazardous-area wiring, the transmitter and the field cable all live on the IS side of the module; the backplane, the Flexbus and the cabinet-side logic are safely separated by galvanic isolation. You get eight loops into a single 46 mm wide slot, each with its own fault LED and alarm bit, in a form factor that was designed to be pulled and reseated while the system stays live.
Application Scenarios
A sour-gas compressor station needed eight loops — suction and discharge pressure, seal-gas differential pressure, three temperature transmitters on the casing, a fuel-gas flow meter and a scrubber level. Every transmitter sat in a Class I, Division 1 location, and the existing marshalling cabinet was already full of DIN-rail barriers eating up real estate. Running a 1797-IE8 on a 1797-TB3S base changed the equation. The IS loops landed directly on the terminal base, the module’s own entity parameters did the energy limiting, and the ControlNet Ex drop carried the data back to the ControlLogix scanner. When the level-transmitter cable developed a pinched shield, the channel 4 red LED started flashing and the Local Fault bit flipped in the I/O tree before the level controller ever saw a stale value. Operations isolated the loop at the next safe window; the other seven loops, including the discharge-pressure protection, never left their scans.
Parameter
| Main Parameters | Value / Description |
|---|---|
| Product Model | 1797-IE8 (keyswitch position 3 on the 1797-TB3 / TB3S base) |
| Manufacturer | Allen-Bradley / Rockwell Automation, FLEX Ex I/O family |
| Product Category | Intrinsically Safe Analog Input Module, 8 channels, field-terminated |
| Input Channels | 8 single-ended, non-isolated from each other; galvanically isolated from Flexbus and from the field-side supply |
| Input Signal | 4–20 mA or 0–20 mA, software-selectable; functional range to 0–22 mA for clean overrange/underrange detection |
| Resolution | 16 bit — 65,536 counts across the span, so 4–20 mA resolves to roughly 0.00024 mA per count |
| Accuracy | ±0.1 % of output signal range at 20 °C; temperature drift 0.05 %/°C of span |
| Step Response | 4 ms to 99 % of full scale — the fast member of the 1797 analog trio, suited to rotating machinery and fast loops |
| Update Time | Module-to-adapter: 200 ms best case, 1.6 ms worst case, depending on scheduled connection size and adapter load |
| Loop Powering | Module-supplied 2-wire loop power; U₀ ≤ 23.7 V, I₀ ≤ 93.5 mA, P₀ ≤ 555 mW — the numbers the examiner checks against your IS appraisal |
| Field-Side Supply | Intrinsically safe +V / −V at terminals 34/50 and 35/51; Uᵢ ≤ 9.5 V DC, Iᵢ ≤ 1 A, Lᵢ / Cᵢ negligible |
| Power / Dissipation | 7.5 W field-side consumption, 5.2 W dissipation ≈ 17.75 BTU/hr — size the 1797-PS supply and the cabinet convection accordingly |
| Diagnostics | Per-channel Overrange, Underrange, Local Fault (open/short) and Remote Transmitter Fault; 8 red LEDs + 1 green power LED |
| Filtering | Fixed hardware filter plus selectable firmware digital filter; tune the cutoff for noisy VFD environments or leave it fast for dynamic loops |
| Data Format | Configurable — raw integer, percent of span or engineering units; sign representation set in the module config, not by jumpers |
| Intrinsic Safety | Ex ia IIB/IIC T4A and Ex ib IIC T4; Class I, II, III Division 1 Groups A–D T4; ATEX II (1) 2G Ex ib[ia] IIC T4, c-UL listed |
| Isolation | Galvanic per DIN EN 60079-11: input ↔ Flexbus, input ↔ field supply, supply ↔ Flexbus; no isolation channel-to-channel |
| Environment | −20 to +70 °C operating, −40 to +85 °C storage, 5–95 % RH non-condensing; 15 g shock, 2 g vibration 10–500 Hz |
| Physical | 46 × 94 × 75 mm (1.8 × 3.7 × 2.95 in), ≈200 g; 1797-TB3 (screw) or 1797-TB3S (spring-clamp) base, conductor to 4 mm² / 12 AWG |
| Network | ControlNet Ex native (1797-ACN15 / 1797-ACNR15 adapter); config and diagnostics travel over the scheduled connection — no onboard Ethernet port |
| Lifecycle | Mature / legacy FLEX Ex platform; supplied as new-surplus, refurbished or repair grade, revision-matched |
