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EM20 Modbus Communication

EM20 Modbus Communication
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1 Safety The EM20 M/MH is intended for connection to dangerous voltages giving a risk of electric shock. Refer to the safety/installation instructions in the EM20 Spec Sheet before connecting the communications. WARNING The meter contains no user serviceable parts. Installation and commissioning should only be carried out by qualified personnel For further Information contact your local Eaton organisation or contact us by email: Email: EuropeanESC@eaton.com

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2 Programming Meters fitted with the Modbus option have two additional stages in the front panel programming menu. To enter programming mode: Hold Press repeatedly until the required setup page is displayed. bAUd RATE 9600 Modbus Meter ID Press or to select from the a list of valid baud rates. Press value. Press or to increment or decrement the value within the valid range (1-247). Press value. For full information on entering and using programming mode refer to the latest “EM20 Installation Guide”.

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3 Connection 3.1 Cable Selection A dedicated, screened twisted pair cable is required to provide basic RS485 connection. A second twisted pair may be used for 0V connection if required. The cable should be chosen to suit the data rate and maximum length to be installed. The EIA RS-485-A standard provides curves that relate cable length to data rate for 24 AWG screened, twisted pair, telephone cable with a shunt capacitance of 50pf/m. For baud rates up to 19,200 the standard suggests a maximum length of 1200m for this type of cable. If other types of cable are to be used it is recommended...

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4 Protocol 4.1 Modbus Commands The EM20 M meter supports the following standard Modbus commands: Read Multiple Holding Registers Read Multiple Input Registers Preset a Single Register Sub Function 00 only (Loop Back) Preset Multiple Registers 4.2 Exception Responses If the meter receives a Modbus command, with no errors and a valid address, it will attempt to handle the query and provide an appropriate response. If the meter cannot handle the query a standard Modbus exception response is sent (except broadcast queries). An exception response is characterised by its function byte which has...

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Data Tables 5 Modbus Data Tables 5.1 Using The Tables For convenience, meter data is organised in tables of like information with the same format. An entire table may be read with a single Modbus command 3 (Holding Registers). For compatibility with the Modbus standard each register contains a single data Word (16 bits). Data in the meter is stored as: Unsigned Integer (U-INT) 16-bit data in the range 0 to 65,535. This is used for parameters such as CT prim as this can never be negative. Signed Integer (S-INT) 16-bit data in the range –32,768 to +32,767. This is used for parameters such as...

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Data Tables Energy registers are stored as long integer representations of the number displayed on the meter without decimal point or scaling. For example if the meter displays 123456.78kWh, the Holding Registers 40515-40516 will contain the long integer 12345678. This number may be scaled in Wh or kWh, using eScale as: Wh = Holding Reg[40516] x 10(eScale-3) kWh = Holding Reg[40516] x 10(eScale-6) The eScale constant is set, along with the kWh register resolution and scaling, by the CT primary and nominal voltage programmed settings. The display scaling and eScale therefore remain constant...

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Data Tables System kW System kVA System kvar System PF Frequency Phase 1 Volts Phase 1 Amps Phase 1 kW Phase 2 Volts Phase 2 Amps Phase 2 kW Phase 3 Volts Phase 3 Amps Phase 3 kW Phase 1 PF Phase 2 PF Phase 3 PF Ph1-Ph2 Volts Ph2-Ph3 Volts Ph3-Ph1 Volts Neutral Current Amps Scale Ki Phase Volts Scale Kvp Line Volts Scale Kvl Power Scale Kp Note: All registers in this table have read only access.

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Data Tables Instantaneous readings are provided as signed integer values with no decimal point or legend (e.g. kW or MW). Scaling factors are provided to enable conversion of the raw data to real numbers in basic unit form (amps, volts, watts, VA, or var). These scaling factors are constant values calculated as a function of CT and PT Primary programming. To convert raw data to real numbers: (K-3) Integer number Relevant Scaling Factor Real number result Example: If the meter is programmed with CT Primary=50Amps and PT Primary=415V: LCD values would be scaled as: 50.00A, 240.0V, 415.7VLL...

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Data Tables 5.4 Additional Instantaneous Values Data Modbus Data Address Register 3072 43073 Phase 1 kVA 3073 43074 Phase 2 kVA 3074 43075 Phase 3 kVA 3075 43076 Phase 1 kvar 3076 43077 Phase 2 kvar 3077 43078 Phase 3 kvar Note: All values in this table are Signed Integers with read only access. 5.5 Peak Hold Values Data Modbus Address Register 3328 43329 Peak Hold Ph1 Amps Ki 3329 43330 Peak Hold Ph2 Amps Ki 3330 43331 Peak Hold Ph3 Amps Ki 3331 43332 Peak Hold Ph1 Volts Kvp 3332 43333 Peak Hold Ph2 Volts Kvp 3333 43334 Peak Hold Ph3 Volts Kvp 3334 43335 Peak Hold kW Demand Kp + 1 3335...

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Data Tables 5.6 Meter Setup Data Modbus Address Register 3584 43585 CT Primary 10 - 25,000 Amps 3585 43586 Nominal Volts 10 - 55,000 Volts 3586 43587 Pulse 1 Rate 1-1000 Counts/Pulse 3587 43588 Pulse 2 Rate (= Pulse 1 Rate) 1-1000 Counts/Pulse 3588 43589 Baud 96 = 9600baud etc 3589 43590 Modbus ID 0 – 247 3590 43591 Meter Model 400 Energy Meter = 1, Power Analyser = 3 3591 43592 Meter Type 3592 43593 Firmware Version Eg. 0x14 = 1.04 3593 43594 Current Demand Period 1 = 10Sec, 2=20Sec etc 3594 43595 Pulse ON Time 1 = 100ms, 2=200ms etc 3595 43596 Security Code 0 - 9999 0–9999kW (scaled as...

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Data Tables 5.9 Total Harmonic Distortion Values Data Modbus Data Address Register 5.10 Power Demand Values Data Modbus Address Register 4608 44609 kW Demand Kp + 1 4609 44610 kVA Demand Kp + 1 4610 44611 Kvar Demand Kp + 1 4611 44612 Peak Hold kW Demand Kp + 1 4612 44613 Peak Hold kVA Demand Kp + 1 4613 44614 Peak Hold kvar Demand Kp + 1 Note: All values in this table are signed Integers. Demand values have read only access while peak hold values have read/write access.

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