Operating Instructions 31
Operating Instructions
Quick Start
To start communicating with a WattNode Modbus meter using a PC, you’ll need to complete the
following steps:
●
Set the Modbus address and baud rate using the DIP switches (see
●
Find and install Modbus software for your PC. For a list of some low-cost programs, see
http://www.ccontrolsys.com/w/Modbus_Software
●
Find and install an EIA RS-485 interface for your PC. The most common versions are RS-232
to RS-485 converters and RS-485 USB interfaces (Ethernet and PCI adapters are also
available). The RS-485 USB interfaces are generally the best choice, because they are USB
powered and don’t require a serial port on your PC.
●
Configure your Modbus software for the correct baud rate, COM port, Modbus RTU (not
Modbus ASCII), N81 parity (no parity, eight data bits, one stop bit), and the WattNode meter’s
Modbus address. If you have ordered
Option EP
, then use even parity (E81) instead.
Now you should be able to send commands to the WattNode meter and receive responses. As a
test, try reading the integer frequency register at
1221
. Be sure to request only one register: some
software defaults to reading 100 registers, which will cause an exception. You should see the AC
line frequency times 10 (approximately 600 for 60 Hz power). If you don’t get a good response,
check the section
Modbus Communication Diagnostics (pg 28)
WattNode Basic Configuration
Out of the box, the WattNode meter is ready to start measuring as soon as the current trans-
former rated amps (
CtAmps
) are configured (the default value is five amps).
●
Set the
register to the correct rated CT amps of your current transformers.
For example, if you are using 100 A CTs, write 100 to register
1603
(16 bit integer register).
Verify Operation
You should be able to read several registers to check that the meter is correctly installed and
measuring power and energy. If your Modbus software supports floating point Modbus registers,
you may want read from the set
Basic Register List - Floating Point (pg 35)
. If you cannot
easily read floating point values, use
Basic Register List - Integer (pg 35)
instead. Verify
registers in the following sequence:
●
(power line frequency)
: should be near 50 or 60 Hz (or 500 or 600 if you are reading
the integer registers).
●
: should match your line-to-neutral voltage.
●
: should be positive (unless you are measuring something that
can generate power like a PV system) and in a reasonable range for the load being measured
(make sure your load is ON). Note: the integer power registers are scaled, so if you expect
to see 75,000 W (75 kW) and instead you see 7500, that is probably because the meter is
reporting integer power in 10 W increments. See
for details.
●
: this will return 0 if there are no errors. If you see any non-zero values, write
them down and check the
section below to determine the
problem.
If you are measuring floating point values and the numbers are way off, your software may be
combining the floating point registers in the wrong order. Compare the values to the integer regis-
ters and check to see if your software has an option like “Float - swapped” or “Float - reversed”; if
so, see if this fixes the problem.
●
If you don’t get reasonable results, check
Measurement Troubleshooting (pg 26)
above.
