Eastron SDM120-Modbus

Compatibility

Compatible with EpiSensor Edge over Modbus RTU.

Connect its RS-485 port to a Modbus Interface or to a serial interface on the Gateway. Edge polls it with its Modbus client.

Edge reads 21 values from it, listed under Interface.

Connect it with

• 
  Modbus Interface ZMB-3X
  From €399 ex VAT Configure Modbus Interface
• 
  Gateway ZGW-20
  From €899 ex VAT Configure Gateway

Specifications

Separate import and export counters make the meter useful at a single-phase grid connection or on a generation circuit. The installation point determines what those counters mean: generation measured at the inverter is different from export measured at the site boundary. For tenant charging, establish that the exact purchased variant and installation meet the applicable metering requirements; an accuracy class alone is not billing approval.^1, 3

Power

Self-powered from the measured supply. Draws no more than 2 W and 10 VA from the circuit it measures.¹

Nominal voltage

230 V or 120 V AC, operating from 80 to 120 % of nominal¹

Current

0.25 to 5(45) A direct connected¹

Frequency

50 or 60 Hz¹

Active energy accuracy

Class 1 (IEC 62053-21); Class B (EN 50470-3)¹

Reactive energy accuracy

Class 2¹

Voltage and current accuracy

0.5 %¹

Legal metrology

MID B+D certified, certificate 0120/SGS0141¹

RS-485 port

Modbus RTU, up to 64 meters and 1,000 m per bus¹

Pulse outputs

Two passive outputs: one fixed at 1000 imp/kWh, one configurable¹

Display

Backlit LCD, up to 999999 kWh¹

Dimensions

18 × 118 × 64 mm (W × H × D), one DIN module¹

Protection

IP51, indoor use¹

Operating temperature

-25 to 55 °C, up to 90 % RH non-condensing¹

Where it is used

• Solar PV generation and export metering on single-phase inverters, from the separate import and export kWh registers.

  Solar PV monitoring

• Tenant and departmental consumption monitoring on single-phase circuits; select the approved meter variant and installation arrangement separately where readings support billing.

  Tenant submetering and cost allocation

• Bringing single-phase meters already on a Modbus bus into a BMS or SCADA system through Edge.

  Modbus meter integration for a BMS or SCADA system

Interface

Read the complete four data bytes, high register first as in the manufacturer voltage example. Keep transport bytes and the RTU CRC out of the float decoder.²

Separate import and export counters preserve flow direction. A configurable total-energy counter is not automatically the same as imported energy.²

The newer SDM120-M V1.0 manual specifies 9600 bit/s by default. Check the installed generation and its display instead of applying the older protocol default.³

Setup

1. Check the model

   Only the SDM120-Modbus, and the newer SDM120-M, has the RS-485 port. The SDM120-Pulse has pulse outputs only and the SDM120-Mbus speaks M-Bus.¹

2. Wire the bus

   Run a two-wire RS-485 pair from a ZMB-31 or the Gateway's serial interface to the meter's A and B terminals, A to A and B to B. One bus can carry 64 meters over up to 1,000 m.¹

3. Set the address and speed

   Scroll to the address, baud rate or parity page and hold the front button for 3 seconds to change it. Each digit is stored 4 seconds after the last press. Give every meter on the bus its own address from 1 to 247.³

4. Match Edge to the meter

   Set the Edge Modbus client to the meter's address, baud rate and parity. The SDM120-Modbus protocol document gives address 1, 2400 bit/s, no parity and 1 stop bit as the defaults.²

5. Prove a complete voltage read

   For device address 1, request RTU bytes 01 04 00 00 00 02 71 CB: FC04, PDU address 0, quantity 2, CRC low byte first. Eastron’s example response carries 43 66 33 34 as its four data bytes. High-register-first float32 gives approximately 230.2 V. Compare against the simultaneous display before enabling the rest of the template.²

Common questions

What baud rate does the SDM120-Modbus use?

The SDM120-Modbus protocol document gives 2400 bit/s as the default, with 1200, 4800 and 9600 bit/s as the other choices. The newer SDM120-M ships at 9600 bit/s and adds 19200 and 38400 bit/s. The meter shows its rate on the display, so check it there if a new meter does not answer.^2, 3

Why does the meter return an error when I read one register?

Every value is a 32-bit float held in two registers. The meter rejects a request whose start address or register count is odd, because it would split a float, so always read in pairs from an even address.²

Are the register addresses zero-based?

Yes. Eastron numbers the input registers from 30001, and this page gives the address sent on the wire. Voltage, register 30001, is address 0, and Total active energy, register 30343, is address 342 (0156 hex).²

Does it measure exported solar energy?

Yes. It measures active and reactive energy in both directions and keeps separate counters, with import active energy at address 72 and export active energy at address 74.^1, 2

What does the total active energy register count?

By default it counts import plus export. A holding register at F920 hex switches it to import only, or to import minus export, which matters if you use the total for billing.²

Can the SDM120-Modbus be used for billing?

Check the approval markings and certificate for the exact meter variant and the requirements that apply to the installation. Class B describes metrological performance; it does not on its own establish that any SDM120 installation is approved for tenant billing. Use import energy explicitly where the charging basis is imported electricity.¹