Resolving HW Config Error 'Max. light test time (ms) 0: Value 0.1 is not within the range [0.6 ... 5.0]' During PCS 7 Migration

During SIMATIC PCS 7 project migration from V7.1 to V8.2 or V9.x, compiling HW Config fails with error '[1(4),-,7,-] Max. light test time (ms) 0: Value 0.1 is not within the range [0.6 ... 5.0]' because updated fail-safe hardware catalog profiles enforce a stricter minimum light test time (0.6 ms) on fail-safe digital output (F-DO) modules (such as ET 200M or ET 200S F-DO cards). In PCS 7 V7.1, earlier firmware profiles permitted values down to 0.1 ms. To resolve this error, open the properties of the faulted F-DO module in HW Config, navigate to the F-Parameters tab, provide the authorized Safety Program Password, and increase the 'Max. light test time' parameter to >= 0.6 ms (typically 1.0 ms or 2.0 ms) before recompiling.

Executive Summary

Migrating legacy SIMATIC PCS 7 projects (such as V7.1 SP4) to modern releases (such as V8.2 or V9.1) requires upgrading hardware catalog descriptions and fail-safe profile definitions. During HW Config compilation of migrated S7-400H or F-Systems stations, engineers frequently encounter compilation aborts stating that the system data could not be reached because the hardware configuration is inconsistent, specifically pointing to an F-DO module whose light test time (e.g., 0.1 ms) violates new range limits [0.6 ... 5.0]. Because fail-safe parameters are cryptographically protected, modifying this setting requires the safety program password. This guide details the root cause, parameter adjustment procedure, and safety verification requirements.

Architecture and Fundamental Mechanics

The light test mechanism on Siemens fail-safe digital output modules performs dark and light tests to verify circuit integrity:
1. Light Test Mechanics (1-Test):
To detect short-circuits to P-potential (cross-faults) and verify internal MOSFET switchability, the F-DO module periodically turns off a de-energized output for a microsecond duration, or turns ON an OFF-state channel briefly (the light test). If the light test pulse is too short (e.g., 0.1 ms), parasitic circuit capacitance and line impedance can prevent accurate internal diagnostic feedback.
2. Catalog Rule Evolution Between V7.1 and V8.2+:
In S7 F-Systems and PCS 7 V7.1, older module catalog profiles allowed light test times as low as 0.1 ms. To improve diagnostic reliability and comply with updated IEC 61508 / EN ISO 13849 safety certifications, Siemens revised the hardware profile rules in newer STEP 7 hardware updates (HSP), raising the minimum allowable parameter boundary to 0.6 ms.
3. Safety Program Password Protection:
Fail-safe parameters are part of the safety configuration. HW Config locks F-parameters to prevent unauthorized tampering. Altering any F-parameter (such as light test time, F-monitoring time, or discrepancy time) invalidates the safety signature and strictly mandates safety password authentication.

Step-by-Step Implementation Procedure

Identify the Faulted Module in HW Config:
a. Read the compilation error log: [1(4),-,7,-] identifies Rack 1, Submodule 4, Slot 7.
b. Open STEP 7 HW Config and navigate to the specified slot containing the fail-safe digital output module (e.g., SM 326 F-DO 10xDC 24V/2A).
Authenticate Safety Access:
a. Double-click the F-DO module to open its Object Properties.
b. Navigate to the 'Parameters' or 'F-Parameters' tab.
c. HW Config prompts for the 'Safety Program Password'.
d. Enter the authorized password for the safety program to unlock editing.
Adjust the Maximum Light Test Time:
a. In the module parameters list, locate the channel group setting 'Max. light test time (ms)'.
b. Notice the highlighted red or yellow field showing 0.1.
c. Change the value from 0.1 to a valid value within [0.6 ... 5.0] ms (the Siemens recommended default is 1.0 ms or 0.8 ms depending on field actuator load capacitance).
d. Verify that all channel groups on the module meet or exceed the 0.6 ms threshold.
e. Click OK to accept the parameters.
Save, Compile, and Validate Safety Signature:
a. In HW Config, execute Station -> Save and Compile.
b. Confirm that the configuration compiles cleanly without error.
c. Open the Safety Program dialog (Options -> Safety Program) in SIMATIC Manager.
d. Verify the new Safety Program collective signature and compare against plant safety change records.
e. Compile CFC charts and perform a controlled download to the fail-safe controller.

Verification

In HW Config, execute Station -> Consistency Check: verify 0 errors and 0 warnings.
In HW Config Test Mode (online), monitor the F-DO module: confirm all channels report healthy status without light test fault diagnostic messages.
Verify field actuator behavior: confirm that mechanical relays or solenoid valves connected to the F-DO module do not glitch or chatter during the 0.6 ms to 1.0 ms light test pulse.
Check the CPU Diagnostic Buffer: confirm no F-periphery passivations or communication faults are logged.

Limitations and Operational Precautions

Adjusting F-parameters alters the safety collective signature of the safety program. Under IEC 61508 and functional safety regulations, this modification represents a safety-related change that must be documented, reviewed, and re-validated by a qualified functional safety engineer.

Engineer FAQ

Why did this error only appear after migrating to PCS 7 V8.2?

Newer versions of STEP 7 and S7 F-Systems incorporate updated hardware descriptions (HSPs) that enforce updated international safety standards, which restrict light test times to >= 0.6 ms.

Can solenoid valves or relays trip due to an increased light test time?

Standard industrial solenoids and relays have mechanical response times of 10 to 30 ms and will not react to a 1.0 ms test pulse. If high-speed electronic inputs are connected, consult manufacturer datasheets.

What if I don't know the Safety Program Password?

The safety password is required by safety standards to modify F-parameters. Without it, safety parameters cannot be altered in HW Config. You must retrieve the authorized password from plant safety documentation.

Can the light test be disabled completely?

On certain F-DO modules, dark test / light test can be deactivated by selecting 'Deactivate' if the connected actuator does not tolerate test pulses, but this may derate the attainable SIL rating.

Does changing the light test time require an AS STOP?

Downloading modified hardware configurations to safety I/O modules generally requires an AS STOP or CIR (Configuration in RUN) procedure if supported by the CPU 410-5H / 400H release.