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5.2
Digital Interface
5.2.1
M-Bus (Meter Bus)
The M-Bus (Meter Bus) is a field bus for recording consumption data. Transmission runs serially
on a reverse polarity protected two-wire line. The EE741 flow sensor as M-Bus slave requires
a separate supply voltage. There is no prescribed specific topology (line or star) for the wiring.
Normal phone cable of type J-Y(St)Y Nx2x0.8 mm can be used. The max. cable length per
segment (primary addressed) is 250 m (820 ft).
The table below shows the structure of the consumption data sent by the sensing unit:
Header
68
4F 4F
68
08
XX
Start user data
72
XX XX XX XX
A5 16
01
09
XX
00
00 00
Data record 1: Volume flow
05
3E
XX XX XX XX
Data record 2: Temperature
05
5B
XX XX XX XX
Data record 3: Mass flow
05
53
XX XX XX XX
Data record 4: Consumption meter status
05
16
XX XX XX XX
Secondary addressing:
In addition to primary addressing, the EE741 flow sensor provides the option of secondary
addressing. The secondary address uses the fields of identification number, manufacturer,
version and medium. The M-Bus Standard https://m-bus.com/assets/downloads/MBDOC48.PDF
describes the exact sequence of the secondary addressing.
M-Bus setup:
Baud rate
Data bits
Parity
Stop bits
Slave address
For several devices on the bus the max. recommended baud rate is 9600.
16
Start of the telegram
L-field (length)
Second starting signal
C-field (RSP_UD)
A-field (address)
CI-field (variable data structure)
Identification number
Manufacturer (0x16A5 ... EUE)
Version
Medium (9 ... compressed air)
Access number (consecutive)
Status
Signature
DIF (32 bit real)
VIF (volume flow in m³/h)
Cur. measured value
DIF (32 bit real)
VIF (temperature in °C)
Cur. measured value
DIF (32 bit real)
VIF (mass flow in kg/h)
Cur. measured value
DIF (32 bit real)
VIF (volumes in m³)
Cur. consumption value
Factory settings
2400
8
EVEN
1
240
Data record 5: Flow velocity
05
7F
XX XX XX XX
Data record 6: Volume flow
04
3B
XX XX XX XX
Data record 7: Temperature
04
59
XX XX XX XX
Data record 8: Mass flow
04
51
XX XX XX XX
Data record 9: Consumption meter status
07
13
XX XX XX XX
XX XX XX XX
Data record 10: Flow velocity
04
7F
XX XX XX XX
End user data
XX
16
Adjustable values
600, 1200, 2400, 4800, 9600
None, odd, even
User Manual EE741 Inline Flow Sensor for Compressed Air and Gases
DIF (32 bit real)
VIF (manufacturer-specific in m/s)
Cur. measured value
DIF (32 bit integer)
VIF (volume flow in 10-³ m³/h)
Cur. measured value
DIF (32 bit integer)
VIF (temperature in 10-² °C)
Cur. measured value
DIF (32 bit integer)
VIF (mass flow in 10-² kg/h)
Cur. measured value
DIF (64 bit integer)
VIF (volumes in 10-³ m³)
Cur. consumption value
DIF (32 bit integer)
VIF (manufacturer-specific in 10-²
m/s)
Cur. measured value
Checksum
End of telegram
8
1 or 2
0...254
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