3300 ACM Installation and Operation Manual Power Measurement Ltd.
G-6 Appendix G: Serial Communications Protocol
ACCESS TO HIGH-RESOLUTION RESULTS
To access the high-resolution values through communica-
tions, a High-Resolution Result Request Flag must be appended to
the end of the Data Field. The Request Flag is a single byte
containing the value FF hex.
If the meter is equipped with firmware revision 1.2.2.0 or
greater, it will respond to a high-resolution Read Register
command as it would for a regular Read Registers command,
except that a special Page 0 Register 03 will be the first register
returned. This register will contain the following information:
03,vv,aa,pp
where 03 = register number
vv,aa,pp = flags for high-resolution Volts,
Amps, and power.
If the Volts flag equals FF hex, any subsequent Volts registers
listed previously will be passed through communications ten
times their actual value for the current packet only. The aa flag will
similarly indicate that any subsequent Amps registers listed
above will be passed through communications ten times their
actual value. If the pp flag is FF hex, this indicates that
subsequent power registers listed previously will be passed as
W, VA or VAR rather than KW, KVA or KVARS.
NOTE
The Page 0 Register 03 can only be read from a
3300 ACM by including the High-Resolu-
tion Request Flag to a Read Registers re-
quest packet. This allows the 3300 ACM to
remain completely compatible with earlier
communications packages which do not
request high-resolution data (e.g. M-
SCADA versions previous to release 4.1).
Refer to the documentation for your com-
munications package to see if the high-
resolution feature is supported.
Similarly, 3300 ACMs equipped with firm-
ware previous to version 1.2.2.0 will simply
ignore the High-Resolution Request Flag,
and return a regular response packet. The
absence of the special Page 0 Register 03 indi-
cates that regular results are being returned
for all registers.
High-Resolution Display Option
HIGH-RESOLUTION REGISTERS
Beginning with firmware release 1.2.2.0, the 3300 ACM is
capable of communicating high-resolution results if the
DISPLAY DECIMALS parameter is set to YES.
High-resolution results are available for the following Page 0
(real-time) registers:
• 10, 11, 12, 13 (Van, Vbn, Vcn, Vln-average)
• 14, 15, 16, 17 (Vab, Vbc, Vca, Vll-average)
• 20, 21, 22, 23 (Ia, Ib, Ic, I-average)
• 33 (KW total)
• 30, 31, 32 (KWa, KWb, KWc)
• 34, 35, 36, 37 (KVARa, KVARb, KVARc, KVAR total)
• 42, 43, 44, 45 (KVAa, KVAb, KVAc, KVA total)
NOTE
High-resolution results are not available for
any minimum, maximum, demand, de-
mand min/max, or energy (hours) mea-
surements.
HIGH-RESOLUTION READINGS
If Volts Line-to-Neutral Total is under 1000 V, or Volts Line-
to-Line Total is under 1732 V, the meter internally scales the
instantaneous voltage reading up by ten.
Amps are always internally scaled up by ten.
If KVA Total is under 40,000 (40 KVA), the meter scales all
instantaneous power values up by 1000. This effectively
converts power readings to Watt, VA, and VAR units.
All increased precision values described above are available
through communications.
Courtesy of NationalSwitchgear.com
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