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SCADA-Modbus® System Guidelines
Appendix E
Problem: The data values being returned by polling the meter with Modbus are not the same as the data
values displayed in the current status screen of the meter.
Response: Confirm that the correct register addresses are being polled.
Check to make sure the register address being polled corresponds to the
correct data channel. For example, if polling for FLOW, make sure the server
or MMI is requesting data from registers 40033–40034.
If polling for several values at the same time, try changing the polling so that
only one value is polled at a time. Then check to see if the polled value
matches a different data channel in the meter. For example, if polling for Level
and it appears that you are getting the data for Velocity instead, you probably
are polling the wrong registers.
Response: Check the data format of the Modbus server.
When configuring a Modbus server or MMI application to poll a 980 Flow
Meter, it is absolutely essential that the correct data format is selected for that
particular data channel (register). For example, when polling for Flow, Level or
Velocity, which are all floating point values, the Modbus server or MMI must be
configured to read these values as floating point values. If the server or MMI is
formatting this data as a data type other then floating point, the values will not
be read or displayed correctly.
Likewise, if polling the meter for engineering units, which are represented by
integer values, such as Flow Units of Measure or Level Units of Measure, the
Modbus server or MMI must be configured to read these values as Integers.
If the server or MMI is formatting this data as any data type other than Integer,
the values will not be read or displayed correctly.
Different Modbus servers and MMI manufacturers have different methods for
configuring the application to the appropriate data type contained within the
register. Contact the server or MMI manufacturer for details on how to
configure the application to read the data in the correct format.