Pulsers
A low frequency (LF) pulser or a high frequency (HF) pulser are integrated into the
standard version of the MQMe Quantometer.
The high frequency (HF) pulser is used to measure the current gas flow to a high level of
precision. One additional HF pulser can be optionally installed on the meter to scan the
turbine wheel. The external HF pulser is designed in accordance with the NAMUR
specifications and is typically connected to an input on the station computer or a
correspondingly equipped volume corrector. Shielded cables should be used for the
connection cables. The rotating blades on the turbine wheel are scanned by the high
frequency sensor as they pass by the surface of the sensor. Each blade that passes the
sensor generates a pulse. Fig. 11 to Fig. 15 are schematic diagrams for the wiring of the
internal pulsers.
The connection to the HF pulser (optional external pulser: scanning of the turbine wheel,
only with an external power supply, the signal cannot be switched by the electronics on
the MQMe) is established via the following connections:
•
pink (-)
•
blue (+)
The standard HF signal is not required for configurations with an integrated volume
corrector. An LF signal is issued instead for the standard flow.
Note:
All of the pulsers are intrinsically safe. If the MQMe Quantometer is installed in
a potentially explosive atmosphere, connections to devices such as a volume
corrector or a station computer that are located outside of the potentially explosive
atmosphere must be established using intrinsically safe circuits, see Fig. 11 to Fig. 15.
RS485-Modbus and M-BUS communication
The meter can be optionally equipped in the factory with either a RS485 Modbus or a M-
Bus interface. The baud rate is 2400 and supports the Modbus RTU protocol. The wiring via
M-Bus and RS485 is illustrated in Fig. 11 to Fig. 15.
4–20 mA output signal
The MQMe Quantometer has a configurable passive two-wire output signal (4–20 mA). The
current flow rate under operating or standard conditions (configuration with a volume
corrector) can be transmitted via the 4–20 mA signal. The flow rate is 0 at 4 mA and a
corresponding maximum value can be set for 20 mA. The maximum deviation is: ±0.5% FS.
The wiring for the analogue 4–20 mA output signal is illustrated in Fig. 11 to Fig. 15.
The maximum value typically corresponds to the Q
max
of the meter or 4 times the Q
max
for
the output of the standard volume (if the volume corrector has been configured) and can
be subsequently adjusted (see section 12, page 29).
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