ABB DSSR122 (48990001-NK) | AC 800M Digital Output Module | Obsolete Relay Output Interface Risk Assessment
ABB DSSR122 (48990001-NK) | AC 800M Digital Output Module | Obsolete Relay Output Interface Risk Assessment - Image 2
ABB DSSR122 (48990001-NK) | AC 800M Digital Output Module | Obsolete Relay Output Interface Risk Assessment - Image 3
ABB DSSR122 (48990001-NK) | AC 800M Digital Output Module | Obsolete Relay Output Interface Risk Assessment - Image 4

ABB DSSR122 (48990001-NK) | AC 800M Digital Output Module | Obsolete Relay Output Interface Risk Assessment

  • Model: DSSR122
  • ABB Order Code: 48990001-NK
  • Brand: ABB
  • System Family: AC 800M (part of the 800xA Distributed Control System)
  • Module Type: Digital Output (DO) module with electromechanical relay contacts
  • Channels: 16 independent Form C (SPDT) relay outputs
  • Function: Provides isolated, high-voltage switching capability to control field devices such as motor starters, solenoid valves, alarms, and small contactors directly from the AC 800M controller
  • Lifecycle Status: Obsolete (no longer manufactured by ABB)
  • Procurement Risk: High — limited verified inventory; often paired with obsolete termination units (e.g., DSSR122 requires specific baseplate/termination like DSTC120 or DSTC160)
  • Critical Role: Enables direct actuation of critical plant equipment; failure can disable safety interlocks, shutdown sequences, or process control actions
Category: SKU: ABB DSSR122 48990001-NK

Description

Key Technical Specifications

Parameter Specification
Output Type Electromechanical relays (Form C: Normally Open + Normally Closed)
Contact Rating 250 V AC / 30 V DC, 2 A resistive per channel
Isolation Channel-to-channel and channel-to-backplane isolation via relay architecture
Backplane Interface Connects to AC 800M I/O baseplates (e.g., TB840A, TB850)
Termination Requirement Requires compatible termination unit (e.g., DSTC120 for screw terminals or DSTC160 for spring-clamp)
Diagnostic Capability Basic module status via LED indicators (Power OK, Fault); no per-channel feedback
Redundancy Support Not inherently redundant; redundancy must be implemented at system level (e.g., dual modules controlling same device via logic)
Mounting Standard AC 800M rack with baseplate
Certifications CE, UL, CSA, IEC 61131-2 compliant

 

System Role and Operational Impact

The DSSR122 is commonly deployed in applications requiring direct, high-voltage switching without external relays—such as:

  • Emergency vent valve actuation
  • Firewater pump start commands
  • Alarm horn/strobe activation
  • Local panel indicator control
  • Small motor or heater control in auxiliary systems

Because it uses physical relays, it can switch both AC and DC loads up to its rating, offering flexibility unmatched by solid-state DO modules. However, this also introduces mechanical wear: each relay has a finite life (typically 100,000–500,000 operations), and frequent cycling accelerates contact erosion or welding.

In a failure scenario:

  • A stuck-open relay prevents command execution (e.g., valve won’t open during ESD)
  • A welded-closed relay may cause unintended actuation (e.g., pump starts unexpectedly)
  • No per-channel diagnostics mean faults are often only detected during functional testing or process deviation

Since the DSSR122 is passively monitored, a failed relay may go unnoticed until needed—posing latent risk in safety-critical loops.

 

Reliability & Common Failure Modes

Despite robust design, the DSSR122 exhibits predictable aging issues after 10–15 years:

  1. Relay Contact Degradation
    • Arcing during load switching erodes contacts, increasing resistance or causing intermittent connection
    • Inductive loads (e.g., solenoids) accelerate wear if not properly suppressed
  2. Coil Driver Failure
    • Internal transistor or driver IC fails due to thermal stress, preventing relay energization
  3. Mechanical Fatigue
    • Repeated operation leads to spring weakening or armature misalignment
  4. Termination/Baseplate Issues
    • Corrosion or loose connections in the DSTC120/160 termination block mimic DO failures
  5. LED or Status Circuit Faults
    • False “OK” indication masks internal failure

Recommended Maintenance:

  • Perform annual functional tests using 800xA or manual forcing
  • Use snubber circuits or flyback diodes on inductive loads to extend relay life
  • Monitor operation counters (if logged in application logic)
  • Replace units showing excessive click delay or inconsistent response

ABB DSSR122 48990001-NK

ABB DSSR122 48990001-NK

 

Lifecycle Status & Migration Strategy

ABB has discontinued the DSSR122 (48990001-NK) with no direct replacement in current AC 800M portfolios. Newer systems favor solid-state digital outputs (e.g., DSQCxxxx series) or remote I/O with Ethernet for reduced maintenance.

However, solid-state modules cannot directly switch AC loads or provide true galvanic isolation per channel, making migration non-trivial.

Short-Term Mitigation:

  • Maintain tested spares with matching firmware/baseplate compatibility
  • Archive termination block layouts and wiring diagrams
  • Avoid mixing DSSR122 batches—relay characteristics may vary slightly

Long-Term Migration Options:

  1. Replace with Solid-State DO + External Relays
    • Use modern DO modules (e.g., DSAI146) to drive panel-mounted industrial relays (e.g., Phoenix Contact, Omron)
    • Preserves AC switching capability while leveraging newer I/O architecture
  2. Upgrade to S800 I/O Platform
    • Transition to S800 I/O with DO810/DO811 modules and external relay packs
    • Enables remote I/O, better diagnostics, and PROFINET/Ethernet integration
  3. Hybrid Approach for Safety Loops
    • For SIL-rated functions, consider dedicated safety relays or Triconex/SIS solutions instead of general-purpose DO

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