Siwarex CS ET200S First-Time Configuration: Resolving DP V1, HMI, and Calibration Issues

The Siwarex CS weighing module is a compact, low-cost signal conditioner designed to mount directly into a Siemens ET200S distributed I/O station. Despite its modest price point, the CS module supports full scale ranges up to 1000 kg and integrates a 16-bit sigma-delta ADC that delivers 1,000,000 internal divisions, more than sufficient for most process weighing applications. This technical reference is derived from a field commissioning sequence in which a sample WinCC Flexible / TIA Portal project produced dead HMI screens even though the S7 CPU and the ET200S station exchanged diagnostic data correctly. The two root causes discovered—DP V0 versus DP V1 mode on the IM151-1 interface module and a missing block consistency check—are not flagged prominently in the official device manual, and a third class of issues (data type selection in the calibration interface) is undocumented altogether. This article consolidates the official device manual with field-proven configuration practice.

1. System Architecture Overview

The Siwarex CS is mechanically identical to a standard ET200S electronic module. It clips onto the ET200S backplane bus and is addressed through the same I/O area as any digital or analog module in the station. The relevant hardware chain in a typical retrofit application looks as follows:

• CPU: S7-300 (e.g. 315-2PN/DP or 317-2PN/DP) or S7-1200/S7-1500 with PROFINET or PROFIBUS master capability.
• ET200S station: Power module (PM-E or PM-D) → Interface module (IM151-1) → Siwarex CS (1SI module) → terminal modules.
• Load cell: 4-wire or 6-wire strain-gauge type, excitation 4.85 V, sensitivity 1, 2 or 4 mV/V.
• Sense feedback: For long cable runs, 6-wire connection is mandatory so the CS can monitor actual excitation voltage at the load cell terminals via SEN+ and SEN-.

According to the Siwarex CS device manual, the module supports 4-wire and 6-wire load cell wiring. The 6-wire variant is the only one that compensates for voltage drop in the supply leads, which is critical when the load cell is mounted in a control panel location distant from the actual weighing vessel.

2. Prerequisites for First-Time Configuration

Before commissioning, gather the following:

1. Siemens SIMATIC S7 PLC with STEP 7 V5.x (or TIA Portal V13 or later) installed on the programming PC.
2. ET200S station with a DP V1 capable IM151-1 interface module (e.g. 6ES7151-1BA02-0AB0 or later). Standard IM151-1 in DP V0 mode is not sufficient for acyclic data exchange used by the sample project.
3. Siwarex CS (article number 7MH4910-0AA01 or 0AA11 depending on firmware generation) seated on the ET200S backplane.
4. Load cell with a calibration certificate stating its mV/V sensitivity and output at full scale.
5. STEP 7 sample project for the Siwarex CS, which contains the FB/FC block library and WinCC Flexible screens.
6. Engineering unit: kilograms, tonnes or newtons. Decide this before the calibration parameters are downloaded.

3. The Two Root Causes of a "Dead" HMI on First Commissioning

When the sample project is loaded into a real PLC and the HMI screens show no live data—even though the CPU and ET200S are visible on PROFIBUS and the SF/BF LEDs are off—two configuration defects are almost always responsible. They must both be corrected before the parameterisation dialogs in the HMI will work.

3.1 IM151-1 must be set to DP V1, not DP V0

The default PROFIBUS profile for an ET200S IM151-1 is DP V0. This is true even on hardware revisions that physically support DP V1. The Siwarex CS uses acyclic record read/write services (DS_READ / DS_WRITE) which are only available on a V1-class master-slave relationship. In DP V0 mode the cyclic I/O transfer works, the module appears online, and there is no diagnostic alarm—yet no parameter data can be read or written, and the HMI screen values stay frozen at zero.

To enable DP V1:

1. Open HW Config in STEP 7.
2. Right-click the IM151-1 in the station.
3. Select Object Properties → PROFIBUS interface → Operating Mode.
4. Tick DP V1 mode (the option is disabled by default in the standard catalog profile).
5. Save and recompile (Station → Save and Compile).
6. Download the hardware configuration to the CPU.

The Siwarex manual states that the module "supports DP V1" but does not clearly explain that the IM151-1's operating mode must be manually switched from V0 to V1 by the user. This is the single most common stumbling block on first commissioning.

3.2 Block consistency check after any FB/FC modification

The Siwarex sample project ships with pre-compiled FBs (FB 1 SIWAREX, FC 1 NDB, FC 2 DPC and the like) that call each other through symbolic names. If the user opens any of these blocks, edits an I/O pin, or replaces a call, the cross-block interface must be re-validated. Failing to do so leaves the HMI screens referencing stale or broken instances. In one real case the engineer moved a single input pin assignment on the instance DB and only realised the inconsistency when HMI tags continued to display the previously compiled value.

Procedure to force a full check:

1. Select the S7 program in the project tree.
2. Right-click → Check Block Consistency.
3. Wait for the compiler to walk every block in the S7 program tree.
4. Re-download all blocks (not just the changed one) to the CPU.
5. Perform a warm restart or cold restart of the CPU.

This must be repeated every time the parameter interface on FB 1 is changed. The default action (the right-click "Save" alone) is not equivalent to a consistency check.

4. Step-by-Step First-Time Configuration

Once DP V1 is enabled and the block consistency check is clean, the following sequence brings the CS into service. The station address used in the sample project is 256, which corresponds to the I/O area starting at PIW 256 / PQW 256 on the S7 CPU side.

4.1 Wire the load cell

For 6-wire load cells, wire the bridge excitation (EXC+, EXC-) and the sense lines (SEN+, SEN-) to the dedicated terminals on the Siwarex CS terminal module. The CS monitors the actual voltage at the cell through SEN+ / SEN-, which compensates for the voltage drop in long cable runs. The signal lines (SIG+, SIG-) close the measurement bridge.

For 4-wire load cells, the SEN+ and SEN- terminals are bridged to EXC+ and EXC- respectively at the terminal block. Accuracy degrades for cable lengths above approximately 10 m.

4.2 Set the load cell sensitivity

From the HMI, or from the parameter DB s_JUST_DAT.b_SENSITIVITY in the user program, set the load cell sensitivity to one of:

This setting must match the actual sensor certificate. A wrong setting silently halves or quarters the displayed weight with no error alarm.

4.3 Calibrate using the two-point method

The standard scaling procedure on the CS requires two calibration points. The first is the zero point (empty scale) and the second is a known calibration weight (e.g. 80% of full scale). For each point the integrator stores a pair of values:

• s_JUST_DAT.i_CALIB_WEIGHT1 / s_JUST_DAT.w_CALIB_DIGITS1 — the engineering value and the raw ADC count for the zero (or low) point.
• s_JUST_DAT.i_CALIB_WEIGHT2 / s_JUST_DAT.w_CALIB_DIGITS2 — the engineering value and the raw ADC count for the high point (calibration weight).

The default value of w_CALIB_DIGITS1 is approximately 60000 counts at zero, and the high point lands somewhere between 100,000 and 1,000,000 depending on sensitivity and calibration weight. If a calibration weight cannot be applied, the integrator returns an uncalibrated reading and the displayed weight will not be linear. This is by design, not a fault.

4.4 Configure the limit values

The CS supports up to four independent limit switches (min, max, min-min, max-max) for alarm generation. Set the limit values in the same engineering unit as the calibration. Like the calibration weights, the limit values are declared as INT in the sample project block interface, which is a documented limitation—see the next section.

5. Data Type Limitation: INT versus REAL

The Siwarex sample project exposes the limit values, calibration weights, and the gross weight as 16-bit signed integers. The data type is set in the FB 1 SIWAREX interface and the matching WinCC Flexible tags. This means:

• Range is constrained to −32768 to +32767.
• If the engineering unit is kilograms, the maximum displayable value is ±32767 kg, or ±327.67 t with two implied decimal places.
• The "two decimal points" appearing on the HMI screens are not part of the data—they are a display formatting artefact. The underlying integer still holds only the integer part.

This is not a bug; it is the design choice of the sample project. For weighing applications above 32 tonnes per unit, the integrator must be replaced with a custom scaling routine that uses REAL (32-bit floating point) tags. To do this:

1. Edit the FB 1 SIWAREX instance DB to declare the gross/net/limit tags as REAL.
2. Update the FC scaling functions to operate on REAL arithmetic.
3. Update the HMI tags in WinCC Flexible to use REAL (32-bit IEEE-754) variables.
4. Run the block consistency check.

Siemens does not ship a REAL-based sample, and the device manual does not call out the INT ceiling at all.

6. Bypass Path: ADC-Based Custom Scaling

There are legitimate field scenarios in which the full two-point calibration cannot be performed at commissioning time:

• No calibrated test weight is available on site.
• The vessel is already in production and cannot be emptied or loaded.
• Approximate weight is sufficient for the application (e.g. tank level monitoring for a pump interlock).

In these cases, the integrator scaling block (FC 2 DPC) can be bypassed entirely, and a user-written scaling function can be applied to the raw ADC value held in s_JUST_DAT.i_ADC_DIGIT. The procedure is:

1. Disable the FC 2 DPC call in OB 1 / OB 35.
2. Add a new FC that reads i_ADC_DIGIT directly from the Siwarex instance DB.
3. Apply a linear scaling function W_kg = (ADC − ADC_zero) × scale_factor where scale_factor is derived from the load cell certificate and the configured sensitivity (1/2/4 mV/V).
4. Output the result to a REAL tag for use in the HMI and process logic.

The caveat is that the Siwarex module must still have its sensitivity (1/2/4 mV/V) configured, because the ADC input range depends on this setting. The sensitivity is configured via s_JUST_DAT.b_SENSITIVITY and is independent of the calibration database.

7. Load Cell Connection: 4-Wire versus 6-Wire

Siemens publishes both topologies in the device manual. The selection is made by the wiring inside the terminal module:

For a control panel retrofit in which the load cells are physically distant from the Siwarex module (the exact situation that originally motivated the Siwarex CS evaluation), the 6-wire connection is the only viable choice. Note that the Siwarex CF modules (the higher-spec siblings) do not support 6-wire sense monitoring, which is the single feature that drives the selection of CS over CF in many retrofit applications.

8. HMI Integration Details

The sample project uses WinCC Flexible 2008 SP2 or later, and the standard TP177B color panel. Adapting to a PC Runtime is largely transparent because the underlying tag interface (the DB symbols in the S7 program) is unchanged. There are three practical points:

1. Tag update rate: configure a 1-second polling cycle for the weight tags. The CS does not need sub-second updates for process weighing, and faster polling wastes bus bandwidth.
2. Operator input fields: the calibration weight and the limits are entered as INT. The HMI will reject values greater than 32767 unless the project is rebuilt with REAL tags.
3. Status display: the HMI sample exposes a "Bus fault" and a "Module fault" indicator. Both will read FALSE in DP V0 mode, which gives a false sense of security. Always verify DP V1 is active before trusting the "OK" status.

9. Verification Procedure

After completing the configuration, run the following sequence to verify correct operation:

1. In STEP 7, monitor the instance DB online. s_JUST_DAT.i_ADC_DIGIT should vary with the load on the cell.
2. Apply a known test weight (e.g. 10% of nominal). The displayed weight should match within the accuracy specification (typically ±0.05% of full scale for the CS).
3. Trigger each limit value. The corresponding bit in s_JUST_DAT.b_LIMIT_FLAGS should change state and the HMI limit indicator should turn red.
4. Power-cycle the CPU and verify that all parameters are retained. The CS stores calibration data in non-volatile memory on the module, not in the PLC.
5. Unplug the load cell connector. The module should raise a sensor line break diagnostic and the HMI should show a comm-loss indicator.

10. Troubleshooting Matrix

11. Firmware and Hardware Compatibility

The Siwarex CS exists in two hardware revisions, identifiable by the article number suffix:

• 0AA01: original module, FW ≤ 2.x.
• 0AA11: current production module, FW 3.x and above.

The sample project is compatible with both, but the FB library must match the firmware generation. Mixing a V2 sample with a V3 module (or vice versa) results in a parameter length mismatch at startup, and the module falls back to factory defaults with no error indication on the S7 side.

12. Common Pitfalls and Field Notes

• The Siwatool serial cable is not mandatory. The CS can be commissioned entirely from the PLC program and the HMI. Use the serial path only as a last resort.
• The CS stores calibration data on the module itself, not in the PLC's load memory. Hot-swapping the module retains calibration; replacing the CPU does not lose the calibration.
• If a scale was previously working with a Siwarex module on ET100 (the legacy series), the load cell wiring can be reused on the CS without modification in 6-wire mode. This is the primary reason for selecting CS over CF in retrofit applications.
• The PROFIBUS GSD file for the ET200S station must include the Siwarex CS module entry. The catalog "1SI SIWAREX CS" is included in STEP 7 V5.5 SP2 and later; older versions require manual import.

FAQ