KTA-282 Modbus TCP Weather Station Gateway
knots
Knots (Nautical Miles per Hour)
m/s
Metres per Second
ft/s
Feet per second
in
Inch
mm
millimetre
Table 17: Gateway Units Listing
2. The Extra Temperatures apply to the 7 extra, 4 Leaf and 4 soil temperatures from loop 1. For Fahrenheit
readings, Extra Temperatures need to have 90 subtracted from them. For Centigrade readings, Extra
Temperatures need to have 50 subtracted from them.
3. Register 32 is reduced by a factor of 10; the readings returned will be 0.0001 in or 0.1 mm.
Weather Station Polling Period
By default, the gateway asks for data from the weather station every 2.5 seconds (as this is the same interval used
by the weather station to read its sensors). This ensures that the latest weather data is made available to your
controller. In between requests, the weather station sleeps to conserve power.
The polling period can be changed by writing to Modbus register 109. Enter your preferred polling period as a
number in tenths of seconds (i.e for 2.5 seconds enter 25). A longer polling period reduces the weather station’s
power consumption; extending battery life.
Weather Station EEPROM Write (Advanced users)
Beware that some configuration values are set by Davis in the factory and should not be changed. The KTA-282
does not guard against ill-advised use of the EEPROM write command.
The configuration registers of the weather station can be directly altered by the KTA-282. The EEPROM of the
weather station is written using either the EEWR command or BAR= command depending on which EEPROM
register requires manipulation (see Vantage Serial Protocol Docs on the Ocean Controls website). Each argument
of these commands is coupled to a Modbus register. Any weather station EEPROM can therefore be written using
Modbus communications.
The BAR command is of the following format:
BAR= <barometer calibration (in Hg * 1000)> <weather station elevation (in feet)>
The EEWR command is of the following format:
EEWR <address in hexadecimal> <value in hexadecimal>
Sending this string to the weather station will write the byte held in data to the EEPROM location specified by
address. For registers of length 2 bytes, two EEWR commands are required.
The EEPROM write function works as follows:
Modbus Holding
Register
Name
Description
110
EEPROM address
Address of the EEPROM register in the weather station
memory
111
EEPROM Payload
Value to be committed to the memory at the address
specified in Holding Register 110
112
Commit to EEPROM
Write a 1 to this register to activate the EEPROM write
command
113
Barometer Value
Value to be written to BAR_CAL (Barometer argument)
114
Elevation
Value to be written to ELEVATION (Elevation argument)
115
Send BAR Command
Write a 1 to this register to activate the BAR write
command
116
Write success
Upon successful EEPROM write, this register will be
written to a 1
Table 18: EEPROM Write Modbus Register Listing
The weather station must be power cycled for the new EEPROM values to take effect. If your console takes
batteries in addition to a plug pack, make sure both the plug pack
and
the batteries are removed. Wait ten seconds
before reapplying power to ensure the weather station has in fact powered down.
Example (BAR= command):
The user has an external barometer that currently reads 1013.25 mbar (29.9 inHg), and the weather station is
mounted 204 metres (670 feet) above sea level.
7/05/2013
www.oceancontrols.com.au
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