Instruction manual

accQcomm Interface Module
Appendix A Commands, Constants, and Registers
A-9
A.3.1 Explanation of an
Example Output
Reading
Assume the current flow rate value is .446697 m
3
/s.
The accQcomm screen will display a flow rate of .446 m
3
/s. The
Modbus output value will appear as 446697 (Modbus units of
measure for flow are always in cc/sec, as stated above.)
In Table A-3, the two corresponding flow rate registers are 30001
and 30002.
In this case, register 30001 (lower word) contains the value
-12055, and register 30002 (upper word) contains the value 6.
Combine these two values into a 32-bit integer by doing the fol-
lowing:
Convert the decimal values into hex.
Combine the two hex values for a sum of 6D0E9. Converted back
into decimal format, this value becomes 446697. This is the flow
rate in cc/sec. Divided by 1,000,000, this value becomes .446, the
flow rate in m
3
/s displayed on the accQcomm.
A.3.2 Explanation of Volume
Interval Registers
Note that Modbus registers 30015, 30016, 30065, 30066, 30115,
and 30116 do not represent cumulative volumes; they are
interval volumes. To use these values, consider the following
points:
1. Track the ensemble number and only read/process the
incremental volumes when a new ensemble occurs--not
with every scan.
2. On scans when the ensemble number increments, count
the interval volume number(s) and add/subtract from a
running total maintained in SCADA.
This mechanism allows the user to implement a forward
totalizer, reverse totalizer, and/or net totalizer as desired.
Further refinement(s) would be to ensure that the SCADA
system does not miss any updates, and/or check the flow
rate against the incremental total.
3. For positive flow, the forward total will be a positive value,
and reverse total will be zero. For negative flow, the reverse
total will be a positive value, and forward total will be zero.
4. Short update intervals with low flow rates may show a zero
volume due to rounding.
-12055 = D0E9
6= 6