Resolving Inverted or Permanent Green Color on Standard Library Valve Block FB73

When the faceplate and block icon for the classic PCS 7 Standard Library valve block FB73 (VALVE) remain permanently green even when the physical or commanded valve is off/closed, the condition is typically caused by feedback signal misconfigurations in CFC (such as limit switch input V_OPEN stuck TRUE, V_CLOSE missing, or NO_FKB configured incorrectly), or an international color philosophy mismatch. In European/German NAMUR standards, Green indicates the valve is Open/Operating and Grey indicates Closed, whereas American ISA-88 conventions frequently treat Green as De-energized/Safe. Verifying feedback wiring in CFC, inspecting the QOPEN/QCLOSE outputs, and adjusting dynamic color properties in @PG_VALVE.pdl resolves the issue.

Operating State Evaluation in Standard Library Valve FB73

The function block VALVE (FB73) from the classic SIMATIC PCS 7 Standard Library (V6.x / V7.x) controls two-way process valves using single or double solenoid actuators. In the controller program, FB73 calculates the technological state of the valve by evaluating the control output QSTART against two binary feedback inputs: V_OPEN (limit switch open feedback) and V_CLOSE (limit switch closed feedback).

The calculated state is encoded into the technological status word QSTATUS and transmitted to WinCC via Operator Control and Monitoring (OCM). In WinCC, the block icon and the master faceplate (@PG_VALVE.pdl) dynamically animate background colors, status symbols, and text based on the bit combination in QSTATUS.

Root Causes of Permanent Green Indication in WinCC

When a valve faceplate remains stubbornly green despite being closed or de-energized, the failure stems from:

Feedback Signal Inversion or Stuck Limit Switch: If the physical limit switch wired to V_OPEN is an inverted contact (Normally Closed instead of Normally Open), or if the I/O channel is forced HIGH in the hardware image, FB73 evaluates V_OPEN = 1. The block concludes the valve is physically open and sets status bit QOPEN = 1, commanding WinCC to render the green operating color.
No-Feedback Mode Configuration (NO_FKB = 1): If the valve lacks physical limit switches, the parameter NO_FKB must be set to 1. In this mode, the block assumes the valve achieves the commanded state after the configured transit time (MON_TI). If NO_FKB is misconfigured or if output commands remain active, the block remains locked in the Open state.
Color Philosophy Discrepancy (NAMUR vs American Standards):
- NAMUR / DIN Standard (Siemens Default): Green = Valve Open (Flow active / Operating); Grey = Valve Closed (Safe / Resting); Red = Fault (Discrepancy).
- American / Power Utility Standard: Red = Valve Open (Energized / Flow active); Green = Valve Closed (De-energized / Safe).
- If plant operators expect green to signify closed/safe, the default European Siemens animation appears inverted.

Valve Status Bits, Feedback Modes, and Color Mapping Matrix

The following table details feedback input combinations, block status outputs, and WinCC faceplate colors:

Physical Valve ConditionV_OPEN PinV_CLOSE PinFB73 Status OutputDefault WinCC Color (NAMUR)American Standard ColorValve Fully Open1 (High)0 (Low)QOPEN = 1; QCLOSE = 0Solid GreenSolid RedValve Fully Closed0 (Low)1 (High)QOPEN = 0; QCLOSE = 1Solid Grey / WhiteSolid GreenIn Transit (Moving)0 (Low)0 (Low)QTRANS = 1Flashing Blue / YellowFlashing YellowDiscrepancy / Fault1 (High)1 (High)QFAULT = 1Flashing RedFlashing RedNo Feedback ModeIgnoredIgnoredTracks QSTART outputGreen when Open; Grey ClosedInverted if modified

Step-by-Step Diagnostic and Color Correction Procedure

To diagnose and correct the permanent green valve indication:

Audit Online Controller Signals in CFC:
- Open the CFC chart containing the FB73 instance.
- Switch to Online Mode (glasses icon) and add the following pins to dynamic monitoring:
- V_OPEN and V_CLOSE (Feedback inputs)
- QSTART (Actuator command output)
- QOPEN and QCLOSE (Internal status flags)
- NO_FKB (No-feedback mode configuration)
- When the valve is commanded off (QSTART = 0):
- If V_OPEN = 1, the physical switch is stuck or inverted; correct the input wiring or invert the pin logic with a NOT gate.
- If V_CLOSE = 0 on a valve with closed limit switches, transit monitoring times out, but if V_OPEN remains 1, the block retains the Open state.
Check No-Feedback Operation:
- If the valve has no limit switches, verify NO_FKB = 1. Invert or reset the command input SP_OP to confirm QSTART drops to 0.
Adjust Color Animation in Graphics Designer (If Regional Philosophy Required):
- Open @PG_VALVE.pdl (and @PCS7Typicals.pdl) in Graphics Designer.
- Select the valve body graphical symbol and open Object Properties -> Colors -> Background Color.
- Inspect the Dynamic Dialog attached to the color.
- If corporate standards require Green for Closed and Red for Open, adjust the color mapping indices corresponding to QOPEN and QCLOSE.
- Save the picture and reload WinCC Runtime.

Verification

Verify valve state and color transitions:
1. Command the valve to OPEN from the WinCC faceplate. Confirm that QSTART = 1, the valve transitions, and the icon turns Solid Green.
2. Command the valve to CLOSE from the faceplate. Confirm that QSTART = 0.
3. Observe feedback signals in CFC: V_OPEN drops to 0 and V_CLOSE rises to 1.
4. Verify on the WinCC screen that the valve symbol changes cleanly from green to Solid Grey (or configured closed color).
5. Disconnect feedback to simulate transit timeout; verify that the symbol flashes red, confirming active diagnostic alarming.

Limitations and Operational Precautions

Plant-Wide Color Consistency: Never alter the color scheme of a single valve block icon in isolation; changing color conventions must be applied plant-wide to avoid operator confusion.
Template Overwrite Risk: If modifying @PCS7Typicals.pdl, protect the template from being overwritten by OS Project Editor updates.
Safe State Identification: In chemical processes, grey represents an inactive, unpowered resting state. Modifying closed valves to green can obscure active pipeline flow paths.

Engineer FAQ

Why does Siemens use Grey for closed valves instead of Green?

Siemens PCS 7 adheres to German NAMUR and international ISO 9241 ergonomic standards: Green indicates active energy, flow, and operation; Grey/White indicates an unpowered, quiescent, safe resting state.

Can I invert the V_OPEN feedback directly inside FB73?

No, FB73 expects positive logic (1 = Closed, 1 = Open). Inversion must be performed on the digital channel driver (Pcs7DiIn with InvIn = 1) or via an external inverter gate in CFC.

What happens if both V_OPEN and V_CLOSE are 1 at the same time?

This indicates a mechanical or electrical sensor failure (limit switches cannot be simultaneously active). FB73 detects this fault, sets QFAULT = 1, and flashes the faceplate red.