Honeywell 621-9928 (6219928) Product Description

621-9928 (6219928) is a serial link selector module of the Honeywell 621 series (IPC 620/621, TPS, TDC 3000), used to achieve automatic/manual switching, redundancy management and signal routing of multiple serial communication links in traditional DCS systems, ensuring high availability of critical communication links.

I. Basic Information

Brand: Honeywell (Honeywell / Measurex)

Full Model: 621-9928 (6219928)

Series: 621 Series Communication Module (IPC 620/621, TPS, TDC 3000)

Type: Serial Link Selector / Communication Redundancy Switching Module

Production Status: Obsolete (Out of Production)

Weight: Approximately 0.46 kg

Size: Approximately 11.4 × 3.8 × 25.4 cm

Installation: Installed in the 621 series I/O rack

Power Supply: 5V DC (Backplane Bus Power Supply, typical 250 mA)

Common Suffix:

621-9928R: ** Hot Swap ** Version

621-9928R-RP: Refurbished / Repaired Version

II. Core Functions

Multi-Serial Link Switching: Supports 2~4 serial communication links for automatic/manual selection

Communication Redundancy Management: Automatically switches to the backup link within milliseconds when the main link fails

Signal Routing and Distribution: Routes the controller's serial data to different slave stations / devices

Link Status Monitoring: Monitors link quality, disconnections, and fault alarms in real time

Manual/Automatic Modes: Supports local manual switching and system automatic redundancy control

Electrical Isolation: High voltage electrical isolation between channels and system side

System Compatibility: Compatible with IPC 620/621, TPS, TDC 3000, PlantScape systems

III. Communication Specifications

Supported Interfaces: RS-232 / RS-485 / Current Loop Serial Links

Link Quantity: Up to 4 input / 2 output links

Switching Modes: Automatic Redundancy (Auto Failover), Manual Selection

Switching Time: < 10 ms (Automatic Fault Switching)

Communication Rate: 1.2 kbps ~ 115.2 kbps (Fully Compatible)

Isolation Voltage: 2500V AC RMS (Channel - System Side)

Connector: 50-pin D-Sub Interface

Protection: ESD, Overcurrent, Reverse Polarity, Surge Protection

IV. Environmental Parameters

Operating Temperature: 0°C ~ +60°C

Storage Temperature: -40°C ~ +85°C

Humidity: 5–95% RH (No Condensation)

Vibration Resistance: 10–55 Hz, 0.7 mm Double Amplitude

Protection: IP20 (Installed in Cabinet)

Certifications: CE, UL, CSA, 94V-0 Flame Retardant

V. Interface and Status Indicators

Field Interface: 50-pin D-Sub (Multi-Serial Link Access)

LED Status:

PWR: Green (Power Supply Normal)

ACT: Yellow (Data Transmission In Progress)

LINK 1~4: Green (Link Normal) / Red (Fault)

ACTIVE: Green (Current Selected Output Link)

MANU: Yellow (Manual Mode) / AUTO: Green (Automatic Mode)

Bus Interface: 621 Rack-Specific Parallel Bus

VI. Typical Applications DCS Serial Communication Redundancy: Controller ↔ Remote I/O Master-Slave Link Redundancy

Multi-device Communication Switching: One controller switches connections to multiple slave devices

Critical Link High Availability: Safety Communication System for Chemical, Power, and Metallurgical Facilities

Upgrade of Old Systems: Add communication redundancy to 620/621, TPS systems

Data Acquisition and Monitoring: Multi-link Data Acquisition in SCADA System

VII. Model Comparison (621 Series Communication Modules) Table

Parameters 621-9928 621-9927 621-9940

Type Serial Link Selector Serial Interface Module Serial Communication Module

Main Function Link Redundancy / Switching Point-to-Point Serial Communication RS-232/485 Protocol Conversion

Number of Links 4 Inputs / 2 Outputs 1 Path 2 Paths

Switching Function Automatic / Manual Redundancy No No

Isolation 2500V AC 1500V AC 2000V AC

Hot Swap 621-9928R 621-9927R 621-9940R

VIII. Common Faults and Troubleshooting

Link does not switch (AUTO ineffective)

Reason: Main link is not faulty, threshold not triggered, module configuration error

Troubleshooting: Check link signal quality, reconfigure switching parameters, restart module

Communication interruption (after switching)

Reason: Backup link is faulty, wiring error, rate mismatch

Troubleshooting: Test backup link, verify wiring, confirm communication parameters are consistent

Status light abnormal (LINK red light)

Reason: Link disconnected, equipment failure, interface damaged

Troubleshooting: Check cables, replace test equipment, replace module interface

IX. Associated Models

Hot Swap Version: 621-9928R

Serial Interface Module: 621-9927 / 621-9927R

Serial Communication Module: 621-9940 / 621-9940R

I/O Expansion Module: 621-9000 / 621-9001

Digital Output: 621-6700 / 621-6701

Digital Input: 621-4500 / 621-4550