GE PQM II, Instruction Manual

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CHAPTER 7: APPLICATIONS
PQMII POWER QUALITY METER – INSTRUCTION MANUAL 7–7
Event Number must be known to read the Event Recorder in this fashion. However, this
Event Number is usually not known and the entire Event Record must be read. The easiest
way to do this is to read the PQMII Memory Map location 0AD0h (Total Number of Events
Since Last Clear) and loop through each Event Number indicated by the value from 0AD0h,
reading the associated data pertaining to each Event. This requires 1 to 150 serial reads of
170 bytes each. Once this data is obtained, it can be interpreted based upon the format of
each value as described in
7.3: Modbus Memory Map . It is important to note that some
memory map parameters are 32 bits (4 bytes) long and require 2 registers to contain their
value, one for the two high bytes and one for the two low bytes.
Note
The operation of the Voltage Disturbance Recorder is similar to the Event Recorder. The
differences between the two recorders are the Modbus addresses, the event data, and the
number of events (150 compared to 500). Refer to the
7.3: Modbus Memory Map for
additional details.
Note
The PQMII uses two different group of samples. PQMII samples at the rate of 64 samples/
cycle for metering calculations and uses the last 2 cycle data (128 samples) for calculating
the RMS value. An RMS value based on separate group of samples (sample rate of 16
samples/cycle) is used for making faster decisions for pickup and dropout of monitoring
elements.
The event time recorded in the event recorder for monitoring elements is based on the RMS
value from 16 samples but the metered RMS values is based on the previous 128 samples
(2 cycle data) at the time of the trigger. Since the event recorder metered data and trigger
data are based on independent and different periods of sample sizes, the metered data in
the event recorder may be different from the RMS value at the time of the trigger. The
accuracy specifications should not be applied for the data in event recorder.