Operation Techniques; Sampling Technique; Measurement Modes; Real-Time Rms Measurements - Satec System 295 Installation And Operation Manual

4. Operation Techniques

The following overview of the PM295 measurement and operation techniques is
intended to provide an understanding of the way the instrument operates.

4.1 Sampling Technique

The input signals taken on the input terminals are sampled at two rates, in an
alternating fashion, to provide measurements at different frequency ranges. For
general RMS measurements and disturbance monitoring, regular sampling is
performed simultaneously on 7 analog inputs (three voltages and four currents) at a
rate of 32 samples per cycle. The instrument continuously digitizes and acquires
data and stores the results in memory. Analog data is stored in a recirculating buffer
that overwrites the oldest records with currently sampled data. Because acquired
data is not overwritten immediately, it is possible to capture data acquired prior to a
trigger signal to provide pre- and post-event waveform analysis.
Sampling frequency is periodically accelerated from a general rate to an expanded
rate of 128 samples per cycle to provide higher resolution for harmonic
measurements. High-resolution waveforms are sampled simultaneously on 2 inputs ,
voltage and current, for a single phase, meaning that full three-phase harmonic
measurements require three sampling laps.

4.2 Measurement Modes

The PM295 measurement capabilities include:
• real-time true RMS measurements
• sliding averaging
• time (demand) averaging
• thermal averaging
• minimum/maximum recording for all real-time measurements and demands

4.2.1 Real-time RMS Measurements

The PM295 measures the true RMS value of AC voltages, currents, and powers for
non-sinusoidal signals with harmonic components up to order 15. All measurements
are performed over one cycle of the sensed waveform. Either real-time measurement
is available for monitoring and setpoint operation.
56 Operation Techniques