User's Manual

Operation: CVSO OpenWay Register
56 CENTRON® OpenWay™ Meter Technical Reference Guide
Testing Using the Energy/Time Method
As an alternate to the above methods, the energy accumulated by the registers and a
reference standard can be read directly from the display and compared over a period of time.
Energy readings displayed while the meter is in the Test Mode are in floating decimal
format. This will result in maximum resolution for short duration tests.
Recommended Energy Testing Procedures
Testing solid-state meters on test boards designed primarily for electromechanical meters
may sometimes give unexpected results. Erroneous readings could occur on light-load (LL)
tests when the test sequence calls for a light-load test following a full-load (FL) or power-
factor (PF) test. In some cases, PF readings could also be in error when following a FL test.
The errors are always positive and may be a few percent for PF and even greater for LL.
The problem is aggravated on lower voltages and when using large test constants, Kt,
similar to the typical Kh values of comparable induction meters. This problem does not exist
on modern test boards with their latest software.
Test Description
A typical meter test sequence consists of:
1 The voltage and current ramp up at unity power factor to the FL level.
2 A pulse from the meter starts the FL test and another pulse ends it.
3 The phase angle then changes for the PF test. The current may stay at the FL level or
ramp down to zero and back up for the phase angle change.
4 A pulse from the meter starts the PF test and another pulse ends it.
5 The current ramps (directly or through zero) to the LL current level at unity power
factor.
6 A pulse from the meter starts the LL test and another pulse ends it.
Most test boards use jogging (slewing) immediately following a FL or PF test to shorten the
time required for the next test to start. The energy used for jogging may be more than
enough to cause the next pulse from the meter even before the ramping of current or
changing of phase angle is completed. If the trigger to start the next test is armed and ready
during the jogging or transition to the next test level, an unexpected pulse may cause the test
to start too soon. This obviously will result in erroneous readings. Some settling time is
necessary for the test board power, the reference standard, and the meter under test to
stabilize after the change to a new test level.
Most test boards provide a settling time (programmable or fixed) and will not recognize
another test pulse following the completion of a test until the jogging, ramping, and settling
time have all transpired. The CENTRON OpenWay meter needs a settling time of about
three to five seconds after the new test level has been reached before the test starts.
Draft