Power & Energy Error Analysis - Arbiter Systems Power Sentinel 1133A Operation Manual

11.8 Power and Energy
data from a 100 millisecond window), yielding a 50% overlap.
Apparent power (VA) and reactive power (VAR) are determined from the results of the voltage
and current magnitude measurements (see next section), using standard identities. The active power
measurements and reactive power measurements are then compensated for PT and CT corrections
(see below) using a complex multiplication, and corrections are performed for transformer iron and
copper losses, if enabled.
At this point, two different things are done with the resulting measurement data. First, a
determination is made of the quadrant in which this data should be registered (Wh delivered or
received, VARh delivered or received.) The results of each measurement cycle (20/sec) are then
added to the proper set of registers. These registers are stored periodically, and accumulation
restarted from zero. The user may configure the unit for different intervals to register energy.
The second thing that is done with the data is to determine the actual power level. This
number will be displayed on the front panel (as Watts or VARs), and it will be returned via the
serial interface if a simple request for "power" is made. This result is calculated by averaging the 20
power measurements made during each second. Therefore, the update rate for this quantity is once
per second. This data is not registered separately depending on the quadrant, as the energy data
is; therefore, it is theoretically possible, if the direction of power flow changes periodically, that the
sum of measurements reported over the serial interface may gradually depart from the registered
energy data. This is due to the loss of information in the averaging process; the registered data
Temperature Errors, 0–50 C
Current input, resistor TCR
Voltage input, resistor ratio
Voltage reference (x2)
Cal. source, resistor ratio (x2)
Time Stability, 1 year
Current input, resistor
Voltage input, resistor ratio
Voltage reference (x2)
Cal. source, resistor ratio (x2)
Measurement Noise
Total RSS Error, Basic
Calibration Errors
Cal. artifact, Rotek MSB-001A
Traceability to National Standards
Total Error, RSS
Specification (0.025%)
Table 11.1: Power & Energy Error Analysis
Error, ppm
63
50
50
25
25
<20
36
<40
10
117
50
50
136
250
113