ZL0122-0D
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TM
E51C2A, E51C3A Installation Guide
Daisy-chaining Devices to the Power Meter
The RS-485 slave port allows the power meter to be connected in a daisy chain with up to 63 2-wire devices.
–
+
S
120 Ω terminator on the first and last
device of the daisy chain
Shield wire
Notes
• The terminal’s voltage and current ratings are compliant with the requirements of the EIA RS-485 communications
standard.
• The RS-485 transceivers are ¼ unit load or less.
• RS-485+ has a 47 kΩ pull up to +5V, and RS-485- has a 47 kΩ pull down to Shield (RS-485 signal ground).
• Wire the RS-485 bus as a daisy chain from device to device, without any stubs. Use 120 Ω termination resistors at each
end of the bus (not included).
• Shield is not internally connected to Earth Ground.
• Connect Shield to Earth Ground somewhere on the RS-485 bus.
For all terminals:
• When tightening terminals, apply the correct torque: 0.37 to 0.44
ft·lb (0.5-0.6 N·m).
• Use 14-24 gauge (2.1-0.2 mm
2
) wire.
RS-485
Communications
The E51C3A includes a data logging feature that records 10 meter parameters, each in its own buffer.
Configuration
Use register 150 to set the data logging time subinterval. Writing to the storage buffer is triggered by the subinterval timer. The
default subinterval is 15 minutes (at a 15 minute interval setting, the buffers hold 60 days of data). An external timer can be used
over Modbus by setting this register to 0.
Use register 159 to turn on data logging and select either Single Shot or Continuous mode. (default is data logging on, Continuous
mode). In Single Shot mode, the meter records data until the buffer is full. When the buffer is full, the meter stops recording
new readings. Data for this time period is kept, but newer energy information is lost. In Continuous mode, the meter continues
to record energy data as long as the meter is operating. The buffer can only hold 5760 entries at one time, however, so when the
number of records exceeds 5760, the oldest entry is deleted to make room for the newest.
Registers 169-178 contain the pointers to 10 data storage buffers. Each buffer is user-configurable with the Modbus address of the
16-bit data output to be stored. 32-bit data, such as floating point data or 32-bit integer energy accumulators, require two buffers.
However, the lower 16 bits of an integer energy accumulator can be stored in a single buffer (optional).
When the E51C3A is first installed, the buffers contain QNAN data, with a value of 0x8000. This data is considered invalid. If the
buffer is reset at any point, all entries in the buffers are overwritten with this 0x8000 value, indicating that it is invalid. All invalid
data is overwritten as the meter fills the buffer with new data entries.
Reading Data
Use register 158 to choose which buffer to read. When this register value is set to 0, the meter is in data logging mode. Changing
this value from 0 to (1 through 10) switches the meter to reading mode and selects a buffer to read. Data from the selected buffer
appears in registers 8000 to 13760.
Data Logging
(E51C3A only)
Red
Black
Gray
0.37 to 0.44 ft-lb
(0.5 to 0.6 N-m)
Use 14 to 24 gauge wire
