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MIW-SPS-EN-001 - 29 / 11 / 2018
10 - 12
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NOTE
To get correct calculation of the volume flow rate, the correct K‑factor of the
fan / drive has to be written in holding register 17!
■
Input register 7
gives information about the current working range. In Standalone
mode it contains the working range which is set by jumpers 1, 2 and 3. In Modbus
mode it contains the working range set via Modbus RTU (RS485) (mirror of holding
register 12).
■
Input register 8
gives information about the current response time. In Standalone
mode it contains the current response time set by jumpers 4 and 5. In Modbus
mode it contains the current response time set via Modbus RTU (RS485) (mirror
of holding register 13).
HOLDING REGISTERS
(see
Table
Modbus register maps
)
These registers are read / write registers and they can be managed with “Read
Holding Registers” command, “Write single register” and “Write Multiple Registers”
commands. They are separated in parts containing different kind of information.
Part 1:
This part contains information about the unit and Modbus communication settings.
■
Register 1
(40001) contains the address at which the unit replies to the master unit in
a Modbus network. The default address is
'
1
'
. It can be changed in two ways:
1.
Send command “Write Single Register” with address
'
1
'
and write the new address
value.
2.
Connect only your unit to a master controller or use the 3SModbus PC application
and send the command “Write Single Register” to address
'
0
'
(Modbus broadcast
address), and write a new address value.
■
The next two registers
(2 & 3)
contain also Modbus settings. Changes in these
registers change the communication settings. The default Modbus settings are
19200-E-1 as it is stated in the
Modbus Protocol Specification
.
■
The next three registers (4, 5 & 6)
are read only. They keep information about the
hardware and firmware versions.
■
The next four registers (7, 8, 9 and 10)
are not used. They are read only.
NOTE
Writing on these registers does not return Modbus error exception, however it
does not change anything either!
Part 2:
■
Holding register 11
(40011) sets the mode of the SPS differential pressure
transmitter. By sending the command “Write Single Register” with address 11
and data
'
2
'
, the unit is set in Modbus mode. In this mode the range and response
time settings are controlled via Modbus only; in Standalone mode these settings
are controlled by the board jumpers. To change to Standalone mode it is necessary
to send the command “Write Single Register” to address 11 with data
'
1
'
. Once the
user has set the SPS unit in Modbus mode, it automatically sets the default range
0—1.000 Pa (value 4 in holding register 12) and the response time to 1 s (value 1
in holding register 13).
■
Holding register 12
(40012) sets the current range in Modbus mode. The default
value is 4 (0—1.000 Pa range).
■
Holding register 13
(40013) sets the current response time in Modbus mode. The
default value is 1 s.
■
Holding register 14
(40014) defines the maximum pressure limit. The default value
is the maximum of the set range. When the measured pressure is higher or equal
to this value, input register 3 (“Max Pressure Limit Flag”) sets to
'
1
'
, otherwise it
is
'
0
'
. This register accepts values between -100 and 2.000. When a value out of
this range is written, the register returns to its default value. The maximum limit
also depends on the current range. If the maximum limit in holding register 14 is
higher than the maximum of the current range, it automatically becomes equal to
the maximum of the range.
SPS
DIFFERENTIAL PRESSURE
TRANSMITTER
