Honeywell 621-9938R Serial I/O Module High Quality

Product Description

The Honeywell 621-9938R Serial Input/Output Module (SIOM) supports high-reliability serial communication within Honeywell TDC 3000 control architectures. This module manages the complete Serial I/O card file and communicates directly with the 621-9939 Serial Link Module (SLM) in the processor card file. Every design detail reflects Honeywell’s long field experience in mission-critical industrial automation. Moreover, users gain stable performance in both redundant and nonredundant configurations. The 621-9938R suits demanding plants that require dependable serial integration with flexible I/O expansion.

Furthermore, the module supports dual redundant communication paths, ensuring uninterrupted system behavior even during link failures. Its robust electrical design and predictable response times help engineers maintain precise control in complex distributed environments. Therefore, the 621-9938R remains a preferred choice for upgrades, lifecycle extensions, and system expansions in legacy TDC installations.

​Functional Highlights

• Controls the complete Serial I/O card file with deterministic behavior
• Interfaces directly with the 621-9939 SLM, ensuring accurate processor communication
• Supports redundant communication lines for improved system availability
• Handles 8, 16, or 32-point serial I/O layouts, enabling scalable configurations
• Ensures stable communication with proper terminating resistors installed
• Integrates smoothly with Honeywell ISSC 600 and TDC 3000 systems

Technical Specifications

General

• Module Type: Serial Input/Output Module (SIOM)
• System Compatibility: Honeywell ISSC 600 and TDC 3000
• Function: Serial I/O control and redundant communication interface
• Installation Position: Slot N in remote Serial I/O card file
• Weight: 1.85 lbs

Communication

• Communication Ports: Dual redundant serial ports
• Supported I/O Points: 8 / 16 / 32 serial I/O configurations
• Required Termination: 200 or 300-ohm resistors at both link ends
• Interface Module: 621-9939 Serial Link Module (SLM)
• Optional Accessory: 621-9928R Serial Link Selector (SLS)

Electrical / I/O Compatibility

• Analog Input Ranges: 4–20 mA DC, 1–5 V DC, 0–10 V DC
• Digital Input Types: 24 V DC, 120 V AC, contact closure
• Resolution: 12-bit or 16-bit (analog modules)
• Accuracy: ±0.1% of full scale or better
• Isolation: Channel-to-channel and field-to-system

Environmental

• Operating Temperature: 0°C to 60°C (32°F to 140°F)
• Mounting: Rack or chassis mounted

Typical Applications

The 621-9938R fits reliably within distributed control environments where long-term availability and deterministic serial links are essential. Engineers typically deploy this module in:

• Advanced process control systems using Honeywell TDC 3000
• Redundant communication architectures requiring continuous uptime
• Serial I/O expansions in energy, refining, petrochemical, and utility plants
• Modernizations of legacy serial networks that demand high stability

For instance, many operators apply the module to preserve system integrity during staged modernization projects, ensuring smooth communication with existing card files.

Support & Maintenance

Honeywell designed the 621-9938R for long operational life with predictable performance. In addition, its modular installation allows quick replacement during scheduled maintenance. Field engineers appreciate its clear diagnostic behavior and stable communication characteristics, which simplify fault isolation and long-term support planning.

FAQ

Q1: Can the 621-9938R operate without redundancy? Yes. It supports both redundant and nonredundant serial configurations.

Q2: Do I need the 621-9928R Serial Link Selector? Not always. However, the SLS helps manage communication path switching in redundant architectures.

Q3: Which module does the SIOM communicate with in the processor card file? It interfaces directly with the Honeywell 621-9939 SLM.

Q4: What I/O ranges are supported through connected modules? It supports standard analog ranges (4–20 mA, 1–5 V, 0–10 V) and digital voltages (24 VDC, 120 VAC).

Q5: Where is the module normally installed? It installs in Slot N of the remote Serial I/O card file.