Honeywell KCD2 Series Modules: KCD2-SCD-EX1 & KCD2-STC-EX1

Technical Dossier

Product Details And Specifications

Honeywell KCD2 Series: Comprehensive Module Range and Technical Overview

The Honeywell KCD2 series is a family of DIN-rail-mounted signal conditioners and isolators engineered for hazardous-area process automation. Deployed extensively in chemical plants, oil refineries, nuclear facilities, and offshore platforms, KCD2 modules serve as the interface layer between field instruments in Zone 0/1/2 hazardous areas and safe-area control systems including DCS, PLC, and SCADA platforms. The series is manufactured to ATEX, IECEx, and FM certification standards, making it a globally accepted solution for intrinsic safety (Ex i) and non-incendive applications. Its compact 12.5 mm or 17.5 mm housing width enables high-density marshalling cabinet installations, a critical requirement in brownfield plant expansions where rack space is constrained.

The Evolution of KCD2 Architecture

The KCD2 platform succeeded Honeywell's earlier KFD and KFA series isolator families, introducing a standardized 24 VDC bus-powered architecture that eliminated the need for individual module power wiring. Early KCD2 variants (circa late 1990s–2000s) focused on passive isolation for 4–20 mA HART loops. Subsequent generations added active signal conditioning, short-circuit protection, and HART transparency — allowing HART-capable field devices to communicate through the isolator to the host system without signal degradation. The SCD (Signal Conditioner with HART) and STC (Smart Transmitter Conditioner) sub-families represent the mature phase of this architecture, optimized for two-wire transmitter loops in Ex ia IIC environments. As the KCD2 series has entered its mature/end-of-active-production lifecycle for several variants, long-term maintenance support — including tested surplus and refurbished stock — has become the primary sourcing channel for installed-base operators.

KCD2 Full Catalog & Functionalities (SKU List)

The following SKUs represent the verified KCD2 series module range, classified by function:

Smart Transmitter Power Supply / Signal Conditioners (Ex i, HART-Transparent)

• KCD2-SCD-EX1: 1-channel, 4–20 mA HART signal conditioner, Ex ia IIC, 24 VDC bus-powered, DIN rail mount, 12.5 mm width.
• KCD2-STC-EX1: 1-channel smart transmitter power supply with HART pass-through, Ex ia IIC, loop-powered field side, 24 VDC supply side.
• KCD2-SCD-EX1.SP: Variant of KCD2-SCD-EX1 with enhanced short-circuit protection for aggressive field wiring environments.
• KCD2-STC-EX1.SP: Variant of KCD2-STC-EX1 with integrated short-circuit protection and reverse polarity guard.
• KCD2-SCD-EX2: 2-channel version of the SCD-EX1, dual isolated 4–20 mA outputs, suitable for redundant DCS input cards.
• KCD2-STC-EX2: 2-channel smart transmitter conditioner, dual loop supply, HART transparent on both channels.

Switch Amplifiers / Discrete Input Modules (Ex i)

• KCD2-SR-EX1: 1-channel switch amplifier for NAMUR proximity sensors and mechanical contacts in Ex ia zones.
• KCD2-SR-EX2: 2-channel switch amplifier, dual NAMUR input, relay output, 24 VDC bus-powered.
• KCD2-SR-EX2.LB: 2-channel switch amplifier with line break and short-circuit detection on sensor lines.
• KCD2-SOT-EX1: 1-channel solenoid driver for Ex ia solenoid valves, 24 VDC, with output monitoring.

Temperature / Thermocouple / RTD Input Modules

• KCD2-UT-EX1: Universal temperature input module, supports TC (Type J/K/T/E/R/S/B) and RTD (Pt100/Pt1000), 4–20 mA output.
• KCD2-UT-EX1.2O: Dual analog output variant of KCD2-UT-EX1, for split-range or redundant temperature monitoring loops.

Frequency / Pulse Input Modules

• KCD2-FI-EX1: Frequency input module for Ex ia turbine flow meters and pulse-output sensors, 0–10 kHz input range.
• KCD2-FI-EX1.2O: Frequency input with dual 4–20 mA analog outputs for flow rate and totalizer signals.

Power Supply / Bus Modules

• KCD2-PW-EX1: 24 VDC segment power supply module for KCD2 bus rail, 500 mA output, redundancy-capable.
• KCD2-PW-EX2: High-current bus power supply, 1 A output, for high-density KCD2 marshalling racks.

Sourcing Hard-to-Find & Obsolete KCD2 Parts

Several KCD2 variants — including the KCD2-SCD-EX1 and KCD2-STC-EX1 — are no longer in active production by Honeywell. Plants operating legacy DCS architectures (Honeywell TDC 3000, Experion PKS early generations, or third-party DCS with KCD2 marshalling) face a sourcing gap when modules fail or require expansion. DriveKNMS maintains a dedicated inventory of tested surplus KCD2 modules sourced from decommissioned plant assets, authorized distributors, and controlled warehouse stock. Each unit undergoes functional verification before dispatch. For operators requiring long-term maintenance agreements or bulk procurement for planned turnarounds, DriveKNMS provides multi-year supply contracts with guaranteed lead times. Obsolete part numbers are cross-referenced against current Honeywell equivalents (e.g., KFD2 series replacements) where applicable, and migration guidance is available on request.

Quality Control for the KCD2 Range

KCD2 modules incorporate a passive backplane bus and precision analog signal paths that require specialized test procedures beyond standard continuity checks. DriveKNMS applies the following protocol to all KCD2 units: (1) Visual inspection of terminal blocks, conformal coating integrity, and housing for mechanical damage. (2) Bus power injection at 24 VDC nominal with current draw verification against datasheet specifications. (3) Loop simulation using a calibrated 4–20 mA source/sink to verify signal accuracy across the full range (0%, 25%, 50%, 75%, 100% of span). (4) HART communication test using a HART modem to confirm transparent pass-through on SCD and STC variants. (5) Isolation resistance test between field-side and supply-side circuits (minimum 500 VDC, ≥10 MΩ). (6) Burn-in at rated load for 24 hours prior to shipment for refurbished units. All test records are retained and available to customers upon request.