Theory Of Operation - Probewell MT-1/WT3 User Manual

MT-1/WT3 User Guide

Theory of Operation

MT-1/WT3 applies a load to the meter under test, then measures the exact quantity
of energy that passes through the meter. After a predetermined number of disk
revolutions, or a minimum time in the case of a solid-state meter, the test will end,
and the application (Probewell Connect) will display the difference between the
meter and the MT-1/WT3's internal electronic standard.
Current Applied to the Meter
The current applied to the meter under test is achieved by three independent built-
in 50 A synthesized AC current sources. The current level is adjustable and regulated.
The current sources simulate loads at unity and at a lagging power factor of 0.5. They
are isolated and form three independent current loads in closed-link arrangement.
This configuration makes it possible to check a meter without needing to open its
potential link and setting up any wiring.
Voltage Applied to the Meter
The voltage applied to the front jaws is derived from the meter base circuit. For
safety reasons, the voltage is only applied to the front jaws when a meter is inserted.
The voltage is also current-limited.
The front jaws of the MT-1/WT3 are controlled by internal relays used to test self-
contained and CT-rated three-phase and single-phase watthour meter form
configurations with no wire setup necessary.
Built-in Electronic Standard
The MT-1/WT3's built-in electronic standard offers exceptional accuracy thanks to
the use of electronic transducers developed by Probewell. These transducers have
an exceptional long-term stability and linearity and are not affected by temperature.
The electronic standard does not contain any potentiometers or other types of screw
adjustment that could become unstable with time. It uses digital technology to
ensure maximum reliability over time. A DSP processor measures and calculates the
exact energy, active or reactive, that passes through the meter. This technology has
the advantage of a more compact and lightweight electronic standard, with smaller,
lighter electronic components.
Accuracy Test
The MT-1/WT3's electronic standard is calibrated using a primary standard traceable
to NIST and comes with a complete calibration report certifying measurement
accuracy on both Wh and VARh scales over its entire operating range. Accuracy test
on MT-1/WT3 can be conducted in your own laboratory using:
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