Evaluating SIMATIC PDM Requirements for HART Field Devices in SIMATIC PCS 7

In SIMATIC PCS 7 systems, SIMATIC PDM (Process Device Manager) is not mandatory simply to read primary 4–20 mA process variables from HART field transmitters or execute basic closed-loop control. Standard analog HART input modules (such as ET 200M 6ES7331-7TF01-0AB0) digitize the primary current loop value directly into standard S7 process images using APL channel blocks. However, SIMATIC PDM is mandatory if the plant requires acyclic parameterization, remote device calibration, access to auxiliary digital HART variables (SV, TV, QV), or integration with the PCS 7 Maintenance Station.

HART Communication Architecture in SIMATIC PCS 7

HART (Highway Addressable Remote Transducer) technology superimposes high-frequency digital frequency-shift keying (FSK) signals on top of standard 4–20 mA analog current loops. In SIMATIC PCS 7, distributed I/O stations (such as ET 200M, ET 200iSP, and ET 200SP HA) utilize dedicated HART-enabled analog input and output modules.

Communication with HART field instruments operates on two functional levels:
1. Cyclic Analog Signal Exchange: The physical 4–20 mA current signal is sampled by the module's analog-to-digital converter and placed into the cyclic controller process image partition (PIW).
2. Acyclic Digital Data Records: Digital HART commands and diagnostic records (such as device manufacturer IDs, serial numbers, sensor calibration ranges, and auxiliary process variables) are transferred acyclically across the fieldbus using data record routing (SFC58/59 or RDREC / WRREC).

Operating HART I-O Without SIMATIC PDM

If an engineering facility chooses not to procure or install SIMATIC PDM:

Primary Process Control: The controller reads the 4–20 mA primary variable (PV) identically to standard non-HART analog instruments. In CFC, standard APL channel blocks (FbAnIn or PCS7AnIn) process the signal, perform limit checking, and update operator faceplates without software errors.
Hardware Configuration: In STEP 7 HW Config, the engineer inserts the HART module (e.g. 6ES7331-7TF01-0AB0) and parameterizes measuring ranges (e.g., 4–20 mA HART) directly in the module properties dialog.
Physical Handheld Communicators: Field technicians configure zero, span, and damping parameters locally at the transmitter terminals using handheld field communicators (e.g., Emerson 475 or AMS Trex), bypassing the engineering station completely.

Capabilities Requiring SIMATIC PDM and Maintenance Station

Procuring and integrating SIMATIC PDM becomes mandatory when the project specification dictates advanced asset management:

Access to Auxiliary Digital Variables: HART devices provide secondary (SV), tertiary (TV), and quaternary (QV) digital measurements (e.g. sensor temperature or totalized flow alongside primary mass flow). In older PCS 7 releases, PDM or HART auxiliary channel drivers (FbHaIn) are required to unpack these variables.
Centralized Remote Parameterization: Technicians can configure, re-range, and zero transmitters directly from the central Engineering Station without visiting hazardous field areas.
PCS 7 Maintenance Station Integration: Automatic generation of diagnostic screens, asset health dashboards, and electronic device descriptions (EDD) for plant maintenance requires PDM.
Audit Trail and Calibration Tracking: PDM stores calibration logs, parameter comparison archives, and historical device health records required for regulated pharmaceutical or chemical auditing.

Functional Comparison: Basic HART vs PDM Integration

The following table compares system capabilities with and without SIMATIC PDM in SIMATIC PCS 7:

System CapabilityWithout SIMATIC PDMWith SIMATIC PDM InstalledRequired Software / LicensesRead Primary 4–20 mA VariableSupported (Standard PIW)Supported (Standard PIW)Standard PCS 7 Engineering & APLClosed-Loop Control (PIDConL)Fully OperationalFully OperationalStandard PCS 7 AS Runtime POsRead Auxiliary Digital Variables (SV, TV, QV)Unsupported or requires manual SFC readingFully Supported via PDM & HART driversSIMATIC PDM Basic + HART OptionRemote Transmitter CalibrationUnsupported (Requires Field Handheld)Supported from Central ESSIMATIC PDM Single Point or ServerMaintenance Station Asset HealthBasic I/O channel error onlyComplete Instrument Diagnostics & EDDPCS 7 Maintenance Station + PDMDevice Parameter Backup / RestoreManual paper records / HandheldAutomated Electronic Database ExportSIMATIC PDM System License

Note: For greenfield installations requiring NAMUR NE 107 intelligent diagnostics, SIMATIC PDM is strongly recommended.

Verification

Verify basic HART functionality without PDM:
1. In HW Config, configure an ET 200M HART module (6ES7331-7TF01-0AB0) and set channel measuring type to '4..20 mA HART'.
2. Download hardware configuration to the AS.
3. Connect a physical HART pressure transmitter; verify the green channel LED illuminates.
4. In CFC test mode, verify that FbAnIn reads the calibrated 4–20 mA engineering value accurately.
5. In WinCC Runtime, open the analog monitoring faceplate (MonAnL); confirm dynamic updating without communications errors.

Limitations and Operational Precautions

Key operational considerations for HART implementations:
- If SIMATIC PDM is omitted, diagnostic buffer alarms will indicate basic wire break (W#16#0006) or overrange, but will not provide detailed transducer error codes.
- Ensure field cable capacitance does not exceed HART physical layer limits (maximum loop resistance between 230 and 1100 ohms is mandatory for digital FSK transmission).
- If PDM is added later, project hardware configurations must be re-compiled to bind Electronic Device Descriptions (EDDs) to existing instruments.

Engineer FAQ

Can I read HART secondary variables without buying PDM in newer PCS 7 versions?

Yes. Starting in PCS 7 V8.2 and V9.0, modern HART modules support cyclic HART variable mapping in HW Config, allowing up to 4 digital variables per channel to be mapped directly into controller memory without launching PDM.

Does SIMATIC PDM consume PCS 7 Process Objects (POs)?

No. SIMATIC PDM uses its own device-count licensing structure (e.g. PDM 10, 100, or 1000 TAGs) based on the number of configured field devices, separate from AS/OS Process Objects.