Siemens SENTRON PAC3120

Compatibility

Compatible through Modbus RTU

The manufacturer documents local measurement reads that can be configured in an Edge Modbus client.

PAC3120 covered by the July 2024 PAC3120/PAC3220 manual. PAC3220 uses built-in Ethernet and a different native connection path; MID variants and expansion modules require their own scope.

Connect it with

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

Models

Specifications

PAC3120 suits a panel where the collection network is already RS-485. Its local display lets the installer compare a read with the meter itself before enabling a larger map. External CT ratios and wiring topology belong to the measuring configuration; serial settings only determine whether the values can be transported. A successful reply therefore does not establish correct primary current or power direction.¹

Current inputs

External 1 A or 5 A secondary CTs¹

Native communication

RS-485 Modbus RTU¹

Factory serial settings

Address 126, 19200 bit/s, 8 data bits, no parity, 2 stop bits¹

Voltage width

Float32 across two registers; L1-N begins at offset 1¹

Energy width and unit

Double across four registers, Wh¹

Write protection

Hardware write-protection switch; monitoring reads remain available¹

Interface

Documented measurements and integration boundaries for SENTRON PAC3120.

• Phase voltages and currents as two-register Float values.
• Total active power at offset 65 in W and frequency at offset 55 in Hz.
• Demand and power factor, distinct from accumulated consumption.
• Import and export energy by tariff, with four-register Double counters in Wh.

Setup

1. Record the model and measuring configuration

   Record the PAC3120 order code, firmware, auxiliary supply and wiring topology. Configure the actual CT primary and secondary values before relying on current, power or energy.

2. Match serial settings

   Read the installed address, baud rate and framing. For a factory-configured meter the manual gives address 126, 19200 bit/s and 8N2. Set the Edge client to the same values and give every meter a unique address.

3. Read a complete Float at its literal offset

   Use FC03 at offset 1 for L1-N voltage, quantity 2. Do not subtract one from a field explicitly labelled offset and do not begin halfway through a multi-register value.

4. Verify ordering and measurement meaning

   Compare the decoded voltage with the simultaneous display to establish the configured byte and word order. Then check phase current and signed power with the CT configuration and known load.

5. Keep energy and settings separate

   Read the complete four-register Double energy counter and divide Wh by 1000 only when displaying kWh. Preserve tariff and import/export direction. Use the hardware write-protection switch after authorised setup where appropriate.

Common questions

Does PAC3120 have the same Ethernet ports as PAC3220?

No. PAC3120 has built-in RS-485. PAC3220 has the native Ethernet path; the shared manual does not make their ports interchangeable.^1, 2

Why can reading offset 2 fail?

Offset 2 is the second half of the L1-N Float that starts at 1. Siemens requires complete multi-register values; begin at the documented starting offset and read the whole width.¹

Why is the energy total a thousand times too large?

The documented Double energy counters use Wh. Converting to kWh requires division by 1000, once, after the complete value has been decoded. Check tariff and direction as well as units.¹