Connecting LOVATO DMK22 Modbus Energy Meter to WinCC flexible

1. Problem Statement

A field installation uses one or more LOVATO DMK22 modular energy analyzers that expose measurement data over Modbus RTU on RS-485. The operator wants to display voltage, current, power, power factor, frequency, and active/reactive energy on a Siemens HMI running WinCC flexible 2008 (Compact / Comfort / Multi Panel or PC-based Runtime) without inserting a PLC between the analyzer and the HMI.

The challenge: WinCC flexible 2008 is a pure HMI/SCADA runtime. Its internal driver set was designed to talk to specific PLC families — not to arbitrary third-party Modbus slaves. A direct "LOVATO → HMI" link is therefore not a drop-down selection in the connection editor. You must bridge the protocol gap with one of three proven paths:

1. A Siemens PLC acting as Modbus RTU master and forwarding values to WinCC flexible via MPI / PROFIBUS / Ethernet.
2. An OPC DA server (KEPServerEX, MatrikonOPC, Siemens OPC, or a custom Matrikon-style server) that polls the DMK22 and exposes tags that WinCC flexible reads through its OPC channel.
3. A standalone Modbus-RTU-to-Modbus-TCP / PROFINET protocol converter (Anybus, Moxa MGate, Helmholz, Phoenix Contact) that emulates the I/O signature of a Siemens PLC.

Path 2 is the only one that genuinely removes the PLC from the architecture. Path 1 keeps a small PLC (often a LOGO! or S7-200) as a "thin" protocol converter. Path 3 replaces the PLC with a headless gateway but presents a Siemens-compatible interface to WinCC flexible.

2. LOVATO DMK22 Technical Profile

The LOVATO DMK series are expansion modules that bolt onto the DME family of multifunction energy meters. The DMK22 specifically adds a serial communication interface. Key characteristics relevant to WinCC flexible integration:

3. WinCC flexible 2008 Communication Architecture

WinCC flexible 2008 supports two distinct runtime targets:

• WinCC flexible Runtime (PC-based) — installed on a Windows PC; widest protocol support including OPC DA client.
• WinCC flexible Compact / Comfort / Multi Panels — firmware-embedded runtime; protocol support is a subset of the PC runtime.

The complete driver matrix is documented in the WinCC flexible 2008 Communication Part 1 manual (entry ID 18797552) and the follow-up WinCC flexible 2008 Communication Part 2 manual (entry ID 18796876). Drivers are grouped by PLC family:

4. Why a Direct DMK22 → HMI Link Fails

The DMK22 speaks Modbus RTU on a 2-wire RS-485 bus. WinCC flexible 2008 HMI panels expose one of these physical ports:

• RS-232 (PPI/MPI on S7-200 panels)
• RS-422 / RS-485 (PROFIBUS-DP slave interface on some panels)
• Ethernet (RJ45)

Even when a panel provides an RS-485 port, WinCC flexible binds that port to the MPI/PROFIBUS DP-slave protocol stack, not a free Modbus master stack. There is no user-configurable "talk Modbus RTU" mode. This is the technical reason every "direct DMK22 to WinCC flexible" question ends with the recommendation of a PLC intermediary or an OPC bridge.

5. Integration Path A — PLC as Modbus Master

This is the most common field solution. A small Siemens PLC sits on the RS-485 bus, polls the LOVATO register map, and exposes the values to the HMI through its native driver.

5.1 Hardware options

5.2 S7-1200 MB_MASTER configuration sketch

This pattern polls Holding Register 0x0000 (Voltage L-N) from DMK22 slave address 1 every 500 ms:

// Data block "ModbusMasterDB"
// MB_MASTER instance DB

"ModbusMaster".REQ        := TRUE;                // Trigger on scan
"ModbusMaster".MB_MODE    := 1;                   // 1 = Read holding registers
"ModbusMaster".SLAVE      := 1;                   // DMK22 Modbus address
"ModbusMaster".DATA_ADDR  := 0;                   // LOVATO register 0x0000
"ModbusMaster".DATA_LEN   := 1;                   // 1 register
"ModbusMaster".DATA_PTR   := P#DB20.DBX0.0 BYTE 2;// Target in DB20
"ModbusMaster".DONE       => #PollDone;
"ModbusMaster".ERROR      => #PollError;
"ModbusMaster".STATUS     => #PollStatus;

On TIA Portal V15+, the MB_MASTER / MB_CLIENT blocks ship in the "MODBUS" instruction palette. Connect the RS-485 adapter CM 1241 (6ES7241-1CH30-1XB0) or CB 1241 (6ES7241-1CH32-0XB0) to the PLC and configure port parameters to match the DMK22 (default 9600 / 8E1).

5.3 Tag mapping in WinCC flexible

1. Open the WinCC flexible project, choose Connections → SIMATIC S7-1200/1500.
2. Enter the PLC IP and rack/slot.
3. Create an HMI tag of type Word or Int and address the matching DB20.DBW0 area.
4. Repeat for current (register 0x0002), active power (0x0004), reactive power (0x0006), energy (0x0040), etc.
5. Bind tags to IO fields or trend views.

6. Integration Path B — OPC DA Bridge (No PLC)

This is the correct path if you specifically want to remove the PLC. It requires a Windows PC running both the OPC server and the WinCC flexible Runtime.

6.1 Architecture

[DMK22] --RS-485--> [USB/RS-485 converter or COM port] --USB--> [Windows PC]
                                                            |
                                                            v
                                                  [OPC DA Server]
                                                  (KEPServerEX / MatrikonOPC)
                                                            |
                                                  OPC DA 2.0/3.0
                                                            |
                                                            v
                                                [WinCC flexible Runtime]
                                                  OPC channel → HMI tags

6.2 OPC channel configuration in WinCC flexible

1. In the WinCC flexible project tree, right-click Connections → Add Connection.
2. Select driver OPC from the list.
3. On the OPC tab enter the OPC Server ProgID, e.g. Kepware.KEPServerEX.V6.
4. Click Browse Server → Browse Items to import the LOVATO tag list.
5. Create HMI tags with OPC item paths like Channel1.LOVATO_DMK22.Voltage_L1N.
6. Configure acquisition cycle (recommend 500 ms–1 s for power values, 5 s for energy totals).

6.3 KEPServerEX Modbus driver setup (example)

1. Install KEPServerEX V6.x or later.
2. Add a new channel of type Modbus RTU Serial.
3. Set COM port, baud 9600, parity Even, data bits 8, stop bits 1.
4. Add a device with Modbus address 1 (DMK22 slave).
5. Add tags mapped to the LOVATO holding registers:
     V_L1N → 400001 (function 03, 1 register, float, byte swap)
     I_TOT → 400003
     P_ACT → 400005
     E_KWH → 400065 (4-register float)
6. Save and click Quick Client to verify polling before launching WinCC flexible.

7. Integration Path C — Protocol Gateway

If you want a headless box on the shop floor that pretends to be a Siemens PLC, install a Modbus-to-S7 / Modbus-to-PROFINET gateway. Common choices:

• Anybus X-gateway Modbus-RTU → PROFINET (HMS Industrial Networks)
• Moxa MGate MB3170 / MB3270 (Modbus RTU ↔ Modbus TCP, used as PROFINET converter with an additional head)
• Helmholz NET-Link PRO or Phoenix Contact GW PN/MODBUS

Configure the gateway to read the LOVATO registers and expose them in a memory area that the gateway's PROFINET side presents to WinCC flexible as if it were a SIMATIC S7 input area. The HMI then uses its native S7-300/400 or S7-1200 driver.

8. Step-by-Step: OPC DA Bridge (Full Procedure)

Because Path B is the closest match to the user's original "no PLC" request, here is the complete commissioning sequence.

8.1 Prerequisites

• Windows 10/11 PC with at least one free USB or COM port.
• RS-485 ↔ USB converter (FTDI FT4232H-based recommended, e.g. USR-TCP232-410s or Advantech ADAM-4561).
• 120 Ω termination resistor at the far end of the RS-485 bus.
• KEPServerEX V6.x or MatrikonOPC Modbus Suite.
• WinCC flexible 2008 SP5 with WinCC flexible Runtime license.
• Latest LOVATO DMK22 register map (download from lovatoelectric.com under the DME/DMK product page).

8.2 RS-485 wiring

DMK22 terminal A (D+) ------ twisted pair A ----- USB-485 A
DMK22 terminal B (D-) ------ twisted pair B ----- USB-485 B
DMK22 GND              ----- shield drain  ----- USB-485 GND
                                              [120R across A-B at this end]

8.3 DMK22 setup

1. Power up the DME base unit, navigate to SETUP → COM → RS485.
2. Set address to a unique value (default 1).
3. Set baud = 9600, parity = Even.
4. Set protocol = Modbus RTU.
5. Confirm and exit.

8.4 KEPServerEX configuration

1. Start KEPServerEX Configuration.
2. Right-click Channels → New Channel → Modbus RTU Serial.
3. COM port = the COM number reported by the USB-485 driver. Baud = 9600. Parity = Even. Data = 8. Stop = 1.
4. Click Test Communications. You should see Modbus device 1 acknowledged.
5. Right-click Devices → New Device → Modbus. ID = 1.
6. Add tags from the LOVATO register map. For 32-bit floats, set datatype Float, address format 4xxxx starting at the holding-register base +1, swap mode Byte Swap on Little-Endian hosts.
7. Use Quick Client to confirm values update at the configured poll rate.

8.5 WinCC flexible project

1. Start WinCC flexible 2008.
2. Open the project → Project → Transfer → Transfer Settings → set Runtime to start as service.
3. In the project tree, Connections → Add Connection → driver OPC.
4. OPC Server Name = the KEPServerEX ProgID (e.g. Kepware.KEPServerEX.V6).
5. Click Tags and then Browse OPC Items. Import each DMK22 tag, e.g. Channel1.Device1.V_L1N.
6. Place IO fields, bar graphs, and trend views on a screen. Bind acquisition cycle = 1000 ms.
7. Compile → Start Runtime.

8.6 Verification

1. On the KEPServerEX Quick Client, force a known value (e.g. write a calibration voltage) into the DMK22 side and confirm the HMI screen updates within one acquisition cycle.
2. In the WinCC flexible diagnostic view (Tools → Diagnostics → OPC Diagnostics), confirm OPC quality = Good for every imported tag.
3. Power-cycle the DMK22. OPC quality must degrade to Bad within the configured timeout (default 5 s) and recover to Good when communication returns.
4. Trigger a bus fault (disconnect A/B) and confirm the OPC server logs a "device not responding" entry and the HMI shows the configured fault indicator.

9. Verification Checklist

10. Troubleshooting Matrix

11. Field-Proven Tips

• Always document the LOVATO firmware version printed on the DME label. Register maps shift between firmware variants and the OPC/PLC tag list will silently break after a meter swap.
• Use a Modbus scanner (CAS Modbus Scanner, Modbus Poll) during commissioning to verify the bus before opening WinCC flexible. This isolates wiring problems from HMI configuration problems.
• If the RS-485 cable runs near VFD power cables, use double-shielded cable and ground the shield at the cabinet end only.
• Schedule the energy register poll at 5 s, not 1 s. Energy values change slowly and you save RS-485 bandwidth for instantaneous readings.
• For multi-meter installations, give every DMK22 a unique Modbus address and use the OPC server's "demultiplex" feature to keep the HMI tag names readable (e.g. DMK22_LineA.Voltage, DMK22_LineB.Voltage).
• Configure the OPC server's Reconnect Interval to 2 s and the Timeout to 1 s so the HMI recovers quickly from a temporary RS-485 disturbance.

12. When to Choose Which Path