Resolving Pcs7AnIn Process Value Scaling Shifts When NamurOff Is Enabled in PCS 7 V9.1

In SIMATIC PCS 7 V9.0 SP3 through V9.1 SP2 UC1, setting NamurOff = 1 on the APL analog channel driver block Pcs7AnIn causes the output PV_Out.Value to display the full scale range instead of the scaled process value when connected to non 4-20mA signals (such as thermocouples, RTDs, or voltage inputs). This functional change stems from updated standardization algorithms; resolution requires maintaining NamurOff = 0 for temperature inputs or configuring the hardware driver Mode parameter to 16#202.

Role of Pcs7AnIn and NAMUR NE43 Limit Monitoring

In SIMATIC PCS 7 Advanced Process Library (APL), the Pcs7AnIn block (FB1869) serves as the primary analog input channel driver:
* It reads raw 16-bit integer values from analog input modules (PIW), converts them to engineering units (REAL), applies quality code evaluation, and outputs the structured variable PV_Out.
* NAMUR NE43 Standard: Defines diagnostic failure levels for standard 4–20 mA current loops:
* Current between 3.8 mA and 20.5 mA is treated as valid measuring range.
* Current between 3.6 mA and 3.8 mA indicates measuring range undershoot.
* Current between 20.5 mA and 21.0 mA indicates measuring range overshoot.
* Current $< 3.6 ext{ mA}$ (wire break) or $> 21.0 ext{ mA}$ (short circuit) triggers bad signal status (ST = 16#00).
* The parameter NamurOff allows engineers to disable NAMUR evaluation for non-standard transmitters: setting NamurOff = 1 disables NE43 limits so signals across the entire raw converter range (0 to 27648) are scaled linearly.

Analysis of the Functional Change Between PCS 7 V9.0 SP2 and V9.1

In earlier library builds (PCS 7 V9.0 SP2 and prior):
* Setting NamurOff = 1 had no adverse effect on non 4–20 mA signals such as Resistance Temperature Detectors (RTD: Pt100/Ni1000) or Thermocouples (TC: Type J/K). The block correctly recognized temperature modes and scaled the reading according to the module's 0.1 °C resolution.
* Beginning in PCS 7 V9.0 SP3 and continuing into PCS 7 V9.1 SP2 UC1, Siemens corrected the standardization formula in Pcs7AnIn to address scaling inaccuracies when NamurOff = 1.
* The Side Effect: If NamurOff = 1 is inadvertently enabled on a thermocouple or RTD channel, the updated standardization algorithm bypasses temperature-specific scaling routines and applies the linear full-span formula:
$$ ext{PV_Out.Value} = ext{Scale.High} - ext{Scale.Low}$$
As a result, the faceplate and CFC output display a constant value representing the scale span (e.g., 100.0 or 500.0) rather than the live measured temperature.

Root Cause: Standardization Algorithm Response to NamurOff on Temperature Signals

The issue arises from how Pcs7AnIn interprets the combination of Mode and NamurOff:
* For RTD and Thermocouple modules, Siemens analog cards report temperature values directly in tenths of a degree (e.g., raw integer 250 corresponds to 25.0 °C).
* The driver determines signal processing using the Mode input parameter, typically populated automatically by the PCS 7 Driver Generator (Generate Module Drivers):
* Mode = 16#0201: 4–20 mA current with NAMUR NE43.
* Mode = 16#0202: Temperature measurement (RTD/TC standard).
* When NamurOff = 1 is forced, the internal logic treats the input as a generic unstandardized transmitter, ignoring the intrinsic 0.1 °C scaling and substituting the configured Scale difference.

Remediation Workflow: Parameterizing NamurOff and Mode for Non 4-20mA Channels

To restore correct temperature scaling on Pcs7AnIn instances in PCS 7 V9.1:
1. Reset NamurOff to Default (Recommended):
* In the CFC chart, locate all Pcs7AnIn blocks connected to RTD, Thermocouple, or direct voltage inputs.
* Verify the input parameter NamurOff.
* Set NamurOff = 0 (or FALSE).
* Because NAMUR NE43 applies exclusively to 4–20 mA current loops, setting NamurOff = 0 does not cause premature failure on temperature channels; the module's native wire-break diagnostics handle sensor faults.
2. Verify Module Driver Mode Interconnection:
* Ensure the Mode input pin of Pcs7AnIn is interconnected to the corresponding OMODE_xx output of the diagnostic driver block (MOD_D1, MOD_HA, or MOD_PA).
* In SIMATIC Manager, execute CFC -> Compile -> Changes Only with the checkbox Generate module drivers enabled.
* Confirm that the driver generator sets Mode = 16#0202 for temperature cards.
3. Download Changes to AS: Perform a delta download in RUN mode. The output PV_Out.Value immediately returns to the live temperature measurement.

Verification

In CFC dynamic test mode, inspect Pcs7AnIn.PV_Out.Value: verify that it displays the correct live temperature (e.g., 24.6 °C).
In WinCC OS runtime, open the analog monitoring faceplate (MonAnL): verify that the bar graph and digital readout match field calibration calibrators.
Disconnect the thermocouple lead in the field: verify that Pcs7AnIn.Bad asserts (Bad = 1), PV_Out.ST drops to 16#00, and the WinCC faceplate indicates a wire break.

Limitations and Operational Precautions

Never set NamurOff = 1 globally across all analog input blocks in a master data library; only apply NamurOff = 1 to specific 0–20 mA or non-NAMUR current loops.
If migrating a project from PCS 7 V9.0 to V9.1, review all analog input block parameters before commissioning to prevent undetected scale range freezes.
Disconnecting the Mode pin from the module driver generator prevents automatic detection of hardware card parameter changes.

Engineer FAQ

What is the primary purpose of the NamurOff parameter on Pcs7AnIn?
It disables NAMUR NE43 limit monitoring (3.6 mA to 21 mA) for non-standard current loops, allowing full 0 to 27648 raw scaling.
Why did NamurOff = 1 work on thermocouples in PCS 7 V9.0 SP2?
In V9.0 SP2, the standardization logic ignored the NamurOff setting when temperature mode was detected; V9.0 SP3 corrected the standardization algorithm, exposing this behavior.
What value should NamurOff have for RTD and Thermocouple sensors?
It should always be set to 0 (default).
What raw integer value does an S7-400 RTD card output for 150.5 °C?
The card outputs raw integer 1505 (representing temperature in tenths of a degree Celsius).
How does Pcs7AnIn know what type of hardware card is connected?
Via the Mode parameter, which is automatically parameterized by the PCS 7 Driver Generator during compilation.
What does Mode = 16#0202 signify on Pcs7AnIn?
It signifies a temperature measurement channel with standard RTD or Thermocouple linearization.
What happens to PV_Out if a thermocouple experiences a wire break?
The analog card transmits raw value 16#7FFF, causing Pcs7AnIn to set Bad = 1 and PV_Out.ST = 16#00.
Can NamurOff be modified online in RUN mode?
Yes, NamurOff is a dynamic block parameter that can be modified online without stopping the CPU.
Does Pcs7AnIn support custom thermocouple linearization curves?
Linearization is handled in the hardware module; Pcs7AnIn scales the linearized values delivered by the card.
Where is the documentation for the V9.0 SP3 NamurOff correction published?
In the official Siemens Readme for SIMATIC PCS 7 Advanced Process Library V9.0 SP3 under block improvements.

Technical References

SIMATIC PCS 7 Advanced Process Library (APL) Function Manual (V9.0 SP3 / V9.1)
Siemens Industry Online Support Entry: Pcs7AnIn Standardization and NamurOff (Entry ID 298924)
NAMUR NE43: Standardization of the Signal Level for the Failure Information of Digital Transmitters
SIMATIC S7-400 Automation System Module Data Manual

Related Tags

PCS 7, APL, Pcs7AnIn, NamurOff, Scaling, Thermocouple, RTD, Temperature, Driver Generator, Standardization

Resolving Pcs7AnIn Process Value Scaling Shifts When NamurOff Is Enabled in PCS 7 V9.1