Eastron
DIN-rail Modbus energy meters — SDM series for KNX and solar PV sub-metering at competitive cost.
Eastron Europe manufactures the SDM series DIN-rail energy meters — the most widely specified low-cost Modbus RTU sub-metering solution in European KNX, solar PV, and commercial building installations. The SDM630 3-phase Modbus RTU meter (MID certified, Class B accuracy) provides active energy (kWh), reactive energy (kvarh), apparent energy (kVAh), power factor, individual phase voltages, and currents via a standard Modbus RTU RS-485 interface. At approximately 40-60% of the cost of Carlo Gavazzi EM340, Eastron meters are chosen when budget is the primary driver and MID Class B accuracy is acceptable. Widely available from RS Components, Farnell, SONEPAR, and TBS Electronics across Europe.
Role in our panels
How we use Eastron
The SDM630 (DIN 3-module = 54mm) measures all 3-phase parameters via direct connection to 100A (or via 5A CT secondary for higher currents). Modbus RTU register map: holding registers (function code 03), float32 big-endian: 0x0000/0 = V L1 (V), 0x0006/6 = V L2, 0x000C/12 = V L3, 0x0012/18 = A L1, 0x0018/24 = A L2, 0x001E/30 = A L3, 0x0034/52 = W total 3-phase (Watts), 0x0046/70 = VA total, 0x003C/60 = var total, 0x0048/72 = PF average, 0x0156/342 = Total kWh import (cumulative), 0x0160/352 = kWh L1, 0x0162/354 = kWh L2, 0x0164/356 = kWh L3. Important: SDM630 register map differs from Carlo Gavazzi EM340 — do not assume interchangeability in WAGO CODESYS programs. Download SDM630 Modbus register map from eastroneurope.com. For WAGO 750-893 CODESYS integration: use same float32 big-endian conversion as EM340 but with SDM630-specific register addresses.
Panel wiring for Eastron SDM sub-metering: SDM630 mounts on DIN-rail in distribution panel, RS-485 terminals connected to Modbus bus alongside other meters (max 32 devices at 9600 baud). Two-wire RS-485: terminal A (positive) and terminal B (negative) — Eastron uses opposite polarity convention from some other manufacturers (verify with SDM630 manual page 8 — swap A/B if no communication). WAGO 750-893 + 750-653 RS-485 module reads SDM630 registers via CODESYS Modbus RTU master then publishes to KNX group addresses. Alternatively: Weinzierl KNX ENO 634 Modbus RTU gateway reads SDM630 directly (ETS6 plug-in, no CODESYS required). For solar PV export metering: SDM630 at grid connection point, bidirectional — register 0x004A = import kWh, register 0x0158 = export kWh (solar to grid). KNX self-consumption logic in WAGO: self_consumption = solar_generation - export_to_grid.
Used in these project types
Eastron products
Key components we install
SDM630 3-Phase Direct 100A
MID Class B certified 3-phase 4-wire energy meter, direct connection to 100A, Modbus RTU RS-485 interface, 54mm DIN-rail (3 modules). Measures all phase voltages, currents, active/reactive/apparent power and energy per phase and total. Register map: float32 big-endian, holding registers via function code 03. Baud rate configurable 1200-19200, Modbus address 1-247 via front panel button. For KNX sub-metering via Weinzierl ENO 634 gateway or WAGO 750-893 CODESYS Modbus master.
SDM630 MID Sealed
Identical to SDM630-Modbus but with factory MID seal intact for legal billing applications — do not open or tamper with the seal. Required for tenant energy billing, EV charger kWh billing, and any application where metered data is used for financial settlement between parties. MID seal is broken if enclosure screws are removed — use SDM630-Modbus (non-sealed) for sub-metering where only the building owner reads the data.
SDM120 Single-Phase 45A
Single-phase 45A direct connection energy meter, Modbus RTU RS-485, 18mm DIN-rail (1 module only). Measures import and export energy, power, voltage, current, power factor for individual apartment or circuit metering. At 18mm width, fits in tight distribution boards. For apartment-by-apartment sub-metering on Modbus bus — up to 32 SDM120 meters per RS-485 segment. KNX integration via Weinzierl ENO 634 or WAGO 750-653 RS-485 module.
SDM72D 3-Phase Mid-Size
MID Class B certified 3-phase 100A direct energy meter, Modbus RTU RS-485, 72mm DIN-rail (4 modules). LCD display on front for local readout. For DIN-rail installations where 54mm SDM630 is too narrow or where a larger display is required for on-site reading. Register map compatible with SDM630 for same parameters. Suitable for commercial distribution boards with wider DIN-rail spacing.
SDM230 Single-Phase Wide Range
Single-phase 100A direct connection energy meter with full power quality measurement including THD (Total Harmonic Distortion) per phase. Modbus RTU RS-485, 36mm DIN-rail (2 modules). For premium single-phase circuit monitoring where harmonics data is required — UPS input monitoring, variable speed drive circuit metering, EV charger power quality logging. Registers include THD voltage and current per phase alongside standard energy parameters.
Eastron FAQ
What is the difference between SDM630 and Carlo Gavazzi EM340 for KNX projects?
Both are DIN-rail 3-phase Modbus RTU MID-certified energy meters, but with important differences: SDM630 is approximately 40-60% cheaper (€80-120 vs €180-250 for EM340 depending on supplier). The EM340 has superior accuracy (Class B ±0.5% reference conditions) and Carlo Gavazzi provides better technical support and a clearer register map document. SDM630 also achieves Class B but with a slightly less robust build quality. For tenant billing in high-value properties: use EM340 for its superior documentation and technical support. For solar PV self-metering, general sub-metering, or budget-constrained commercial projects: SDM630 provides the same functional capability at lower cost. Note that the Modbus register maps are different — if switching between SDM630 and EM340 in an existing CODESYS or ENO 634 gateway project, you must update all register addresses.
How do I configure Modbus RS-485 addressing on the SDM630?
Press and hold the front-panel button for 3 seconds to enter programming mode. The LCD shows settings: baud rate (default 9600), parity (default none, 1 stop bit), and Modbus address (default address 1). Use button presses to cycle through settings and values. Important: each meter on the same RS-485 bus must have a unique address (1-247). Set baud rate and parity identically across all meters on the bus. RS-485 wiring polarity: SDM630 terminal labelled + = Data+ (RS-485 A). Terminal labelled - = Data- (RS-485 B). Some Modbus masters label these A and B — match A to +, B to -. If communication fails despite correct wiring: swap A and B terminals. Add 120-ohm termination resistor between + and - at the last device on the bus.
Can SDM630 measure both import and export energy for solar PV systems?
Yes — the SDM630 measures bidirectional energy flow without requiring any configuration change. Register 0x0156 (decimal 342) = total active energy import in kWh (float32 big-endian). Register 0x0158 (decimal 344) = total active energy export in kWh (from load/PV back to grid). For solar PV metering: install SDM630 at the grid connection point (mains meter location), after the DNO meter. When PV generation exceeds load: current flows in reverse through SDM630 — it records this as export energy. WAGO CODESYS or ENO 634 gateway reads both registers. KNX group addresses: GA_Import_kWh (DPT 14.019), GA_Export_kWh (DPT 14.019). Self-consumption calculation: GA_Generation_kWh (from Fronius/SMA inverter Modbus) minus GA_Export_kWh = self-consumed energy.
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