Coils
The coil registers represent functions of the device. The value returned when reading
a coil register indicates the status of the last function execution. If the value is 1, then
the last time the function executed was a success. If the value is 0, then the function
has either not been executed since power on or failed during the last execution. To
execute a function, write 1 to the corresponding register. A response will be returned
immediately and the value of the coil will be set to 0. Once the function completes,
the value of the coil will be set to 1 if the operation was a success. An application
should poll the value of the coil periodically during this time to determine if the function
succeeded. If the coil value does not transition to 1 after at most 10 seconds, then the
operation failed.
Coil 1 – Zero Function
The zero function will attempt to recalibrate the zero point. This may be needed if the
sensor has drifted over time. Note that the zero function will only re-zero the sensor
if the current air velocity is within ±2% of span air velocity of the previous zero. If the
current air velocity is outside the valid band, the zero function will fail and the coil value
will remain 0. If the sensor has drifted far enough that the zero function fails, then the
unit will have to be placed in flow to bring the current air velocity closer to the current
zero, and the zero function will have to be executed multiple times until the actual zero
is reached.
Coil 2 – Span Function
The span function will attempt to recalibrate the maximum air velocity. Note that
accurate span air velocity depends on an accurate zero air velocity. The span function
will fail if the zero function has not been executed within the last 5 minutes.
Coil 3 – Reset factory Defaults Function
The reset factory defaults function resets the zero, span, Velocity K value, Area, and
Use Default K Value variables back to their factory default values.
Coil 4 – Reset Device Function
The reset device function allows this device to be reset remotely from the Modbus
®
Communication Protocol. When the reset device function coil is written with a value
of 1, the device will immediately respond with success. The reset will take place
approximately 5 seconds after the command was received. Writing the value 0 to this
coil has no effect.
Multi-address Support
Multi-Address support allows a register to be read or written to using different byte
orientations specified by the address range. For example, input register 0003 can also
be read at 2003, 4003 and 6003 with different byte orientations as listed in Table 10.
Registers that do not have multi-address support are only available in Big-Endian byte
orientation (Modbus
®
Communication Protocol standard).
APPENDIX V: Setting Modbus
®
Communication Protocol MAC Address of Unit
The address assignment is determined by adding the values for each of the switches
that are in the ON position. The transmitter comes from the factory with all of the DIP
switches, except position 1, in the ON position as shown in Figure 10. The address
of the transmitter would be 127 as it would be 64+32+16+8+4+2+1 = 127. Another
example would be if the address desired was 008, the only DIP switch position in the
ON position would be position 5 as shown in Figure 11
Register Description
Data Type Value Range
Multi-
Address
Supported
0001
0002
0003
0004
Perform Zero Function
Perform Span Function
Reset Factory Defaults
Reset Device
Boolean
Boolean
Boolean
Boolean
0…1
0…1
0…1
0…1
False – True
False – True
False – True
False – True
No
No
No
No
Table 9: Coils
Float/32 Bit Values
16 Bit Values
Register 1 Register 2 Register 1
Byte Order Address Range MSB
LSB MSB
LSB
Big-Endian
Byte Swap
Word Sway
Little-Endian
1 – 2000
2001 – 4000
4001 – 6000
6001 - 8000
A
B
C
D
B
A
D
C
C
D
A
B
D
C
B
A
A
B
A
B
B
A
B
A
Table 10: Multi-address support
.
Switch Position 1
2
3
4
5
6
7
8
Address Value
128 64
32
16
8
4
2
1
Table 11: Device objects
Though the minimum possible address would be address 0 when
all the DIP switch positions were set to OFF, and the maximum
possible address would be address 255 when all of the DIP switches were set to ON,
but the transmitter only has valid address from 1 to 247. Any address outside of this
range will give an error code.
NOTICE
APPENDIX VI: Modbus
®
Communication Protocol Registers
Register Description
Data Type
Value
Range
Multi-
Address
Supported
0001
0002
0003
0004
0005
0006
0007 –
0008
0009 –
0010
0011 –
0012
0013 –
0014
0015 –
0016
0017 –
0018
0019
0020 –
0021
8001 –
8006
8007 –
8012
8013 –
8018
8019 –
8024
Velocity (FPM)
Velocity (0.001 MPS)
Flow (CFM)
Flow (CMH)
Temperature (0.1 °F)
Temperature (0.1 °C)
Velocity (FPM)
Velocity (MPS)
Flow (CFM)
Flow (CMH)
Temperature (°F)
Temperature (°C)
Sensor Operational
Sensor
Communication
Errors
Modbus
®
Application
Firmware Version
Sensor Application
Firmware Version
Modbus
®
Application
Serial Number
Sensor Application
Serial Number
Signed 16bit
integer
Signed 16bit
integer
Signed 16bit
integer
Signed 16bit
integer
Signed 16bit
integer
Signed 16bit
integer
Float
Float
Float
Float
Float
Float
Unsigned 16bit
integer
Unsigned 32bit
integer
String
String
String
String
0…1
0…2
32
-1
False –
True
0…232-
1
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
Table 12: Modbus
®
communication protocol registers
Figure 10
Figure 11
ON
1
2
3
4
5
6
7
8
