Probewell MT-1/WT3, User Manual, Page: 14 / 86

MT-1/WT3 User Guide
Page • 13
Functioning Theory
MT-1/WT3 applies a load to the meter under test, then measures exactly the
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 independents built-
in 50A synthesized AC current sources. The current level is adjustable and regulated.
The current sources allow to simulate loads at unity and 0.5 lagging power factor.
They are isolated and form three independent current loads in closed-link
arrangement. This configuration allows to check a meter without the need to open
the potential link of the meter and no wiring setup is necessary.
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 applied to the front jaws only when a meter is inserted.
The voltage is also current limited.
The front jaws of the MT-1/WT3 are controlled by internal relays allowing to test
self-contained and CT rated three-phase and single-phase watthour meter form
configurations without wiring setup.
Built-in Electronic Standard
The built-in electronic standard in the MT-1/WT3 has an 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 a maximum of 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 obtaining a more compact and lightweight electronic standard
while minimizing 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 done in your own laboratory using: