Executive Summary

A production shutdown was triggered by an unexpected early activation of a timed safety output controlled by the Black Horse F2103a Timer Module (Planar F System).

Configured delay: 3 seconds
Actual measured delay: < 200 ms

This resulted in premature activation of a downstream safety interlock, halting the process sequence.

Root cause was traced to internal timing counter corruption caused by unstable supply filtering.

System Context

Application:

• Controlled restart sequence after safety reset

• Time delay required before enabling motion drives

• Module installed in cabinet operating 24/7

No recent firmware updates.
No mechanical intervention performed prior to incident.

Initial Observations

At 09:42 AM:

• Operator pressed reset

• Motion drives enabled almost instantly

• Safety PLC recorded “Sequence Violation”

• Timer module output LED activated immediately

No error LED present on F2103a.

Hypothesis Development

Because output triggered too early, possible causes included:

1. Parameter corruption

2. External wiring short

3. Internal counter failure

4. Power instability affecting timing logic

Diagnostic Workflow

1️⃣ Configuration Verification

Result: Preset value confirmed at 3.000 seconds.

No configuration drift.

2️⃣ Output Signal Isolation

Output still triggered immediately.

External wiring eliminated as cause.

3️⃣ Supply Stability Check

Measured:

• Nominal: 24.1V

• Under heavy load: 18.7V transient drop (15–20 ms)

Significant voltage dip detected.

Internal Failure Mechanism

The F2103a timer logic depends on:

• Stable regulated supply

• Counter register integrity

• Comparator threshold accuracy

Voltage sag below logic threshold likely caused:

• Counter register reset

• Premature compare event

• Immediate output trigger

Effectively, timer skipped counting phase.

Oscilloscope Capture Findings

Test sequence repeated while monitoring internal logic rail:

• Logic rail dipped below 4.5V threshold

• Timer reset mid-cycle

• Comparator interpreted reset value as “elapsed”

This explains near-instant activation.

Root Cause

Unstable cabinet power supply caused transient undervoltage, corrupting internal timing counter state and resulting in premature output activation.

Corrective Actions

1. Replaced aging 24V power supply

2. Added additional DIN-rail buffer capacitor module

3. Verified voltage dip < 0.8V under full load

4. Performed 50-cycle timing validation test

After correction:

Measured delay: 3.01–3.04 seconds
No further abnormal triggering.

Preventive Engineering Controls

• Maintain ≥30% PSU load margin

• Avoid sharing timer supply with high-current solenoids

• Install voltage monitoring relay

• Log transient events during commissioning

Risk Assessment Note

Unlike delayed trip faults, early-trigger faults can:

• Cause unexpected motion

• Disrupt safe startup sequences

• Bypass intended interlock delay

Therefore, timing integrity must be validated after any power system modification.

Technical Conclusion

When a Black Horse F2103a Timer Module activates outputs prematurely without configuration errors, investigate transient power instability affecting internal timing logic. Stable supply conditions are essential for reliable delay accuracy in Planar F safety systems.