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GF U3000 V2 Ultrasonic Flowmeter
Modbus Supplement to the operating instructions
3.3
Reading Registers
Registers may be read singularly or in blocks. It should be noted that registers are updated once every second in an atomic operati-
on. In this way this register set can be considered a single data point. It should be obvious that reading multiple single registers
cannot ensure that the data returned is from the same data set. If that is not important then reading single registers is an acceptab-
le approach, however, often it is important to read several values at the same time since they relate to the state of the unit at that
time. For this reason, it is recommended that a block of registers be read at the same time. Key values have been grouped to make
this possible. If the local timestamp is important, then start reading at address 100. If not, start reading at address 104. The simplest
way to do this is to use the READ HOLDING REGISTERS command (03).
Note that the units of some measurements are normalised integer numbers and others are IEE754 floating point numbers. For ex-
ample, temperature is an integer reported with a precision of 1/100th of a degree. SNR is also reported this way. Note that the re-
porting precision does not reflect the accuracy the measurement. For the accuracy of the unit’s measurement, refer to the manual.
3.4
Writing Updateable Registers
Registers highlighted as RW are updateable. They provide the ability to update the unit’s configuration. Except for the Regime regis-
ter (register 5, offset 4), all updateable registers can be updated from both the unit and the Modbus, that is that is the unit’s settings
may determine the register contents when reading and the MBM may also manipulate the same parameters.
The Regime register is the only updateable register that is solely owned the MBM. The regime chosen only effects Modbus register
values and has no influence on the unit’s measurement settings. The Regime can be changed by simply performing a write to the
Regime register. Only the bottom five bits will be considered. Four regimes are valid: Metric1, Imperial, US Imperial and Imperial2.
Each regime has a default set of units for each quantity reported. The default unit can be seen in the Notes column for the respective
regime and register, and more concisely, in Table 4, below. Note that a measurement regime of 4 and above will be set the regime
back to 0 (Metric1), the default regime. The Regime register may be set using either the Mask Write Register or Write Single Register
command. The regime register may also be read by the MBM. The regime set by the MBM will only stay set until the unit is restarted.
To ensure the Modbus regime is always restored after a reset, the regime needs to be saved. This is accomplished using the Save
Measurement Regime bit (bit 3) of the Instrument Control Flags register (register 6, offset 5). The procedure for doing this is outlined
in the ensuing paragraphs.
