13
2.4.13 2.4.2.3 Rotating Instruments, Fixed Energy
This technique is usable with standards such as the General Electric Co. IB -10 and the
Scientific Columbus SC-10 meters. In this mode the Model 811A is set to a precise apparent energy
at the rated wattage of the meter. The energy can be selected by the user to register any number of
full turns of the indicating wheel or counts of the register. After connecting the unit under test to the
Model 811A, the Model 811A is placed in the Operate state. The voltage coil of the standard meter
is then disconnected and the register of the meter is reset. With current applied the unit under test is
allowed to 'warm up' though with no voltage applied the register does not indicate anything. When
the voltage coil of the standard is switched on to the Model 811A via external means, such as the
pendulum switch normally supplied with IB-10 type standards, the timing to generate the precise
energy is automatically started. This is accomplished by connecting the "load applied" output signal
to either the "start VAS time-out" or "KVA SEC time-out" (see paragraph 2.4.2.4 for specific
connections on connector P30). At the end of the timing period the output of the Model 811A is
automatically removed. The indicator of the meter under test may then be read to determine
performance.
NOTE
The contacts of the pendulum switch should be bypassed with a capacitor
(such as a 0.01µF 1.5kV disk) to prevent switch bounce from disturbing the operation
of the Model 811A. Otherwise the 811A will revert to the Standby state immediately
after Operate is pressed.
After a test has been completed, the same or new energy data must be entered into the
Model 811A. The same data can be re-entered by pressing the enter key twice.
The load applied signal has been factory adjusted to trigger at 4VA for 120V settings and
8VA for 240V settings. For instruments having a high input impedance, such as a Model SC-10, an
appropriate load resistor (2.5K 120V, 4.7 K 220V) must be attached to the voltage input terminals on
the instrument under test. (See Figure 2-6).
The Auto Standby Switch, located on the calibrators rear panel, must be set to the 'auto'
position (up) to enable this mode of operation and the load applied signal on P30 must be jumpered
to the start VAS or KVAS line time-out. In all other situations the auto standby switch should be left in
the 'down' state. See paragraph 2.4.2.4 for details.
Assume, as an example, a test of such an instrument at 120 volts, 5 amperes, 0.5 PF
lagging, where the register is to be checked at 10 turns. The watt-hour constant (K
h
) is 0.6 watt-
hours/revolution. or 2160 VA-seconds/revolution. Ten complete revolutions of the dial will thus
require 21600 VA-seconds of energy. At a power factor of 0.5, however, this represents 43200 VA-
seconds. Before beginning the test be certain to connect P30 pins 22 and 24.
To enter the settings it is best to begin by resetting the 811A. Then key 120 volts followed by
600 VA to enter the VA setting. Set PF to 0.5 lagging. Next key 43200 VAS; the last digit will enter
the value automatically so it is not necessary to press the enter key. Ensure that the pendulum
switch is open, then press the 811A Operate Control. This applies the current of 5 amperes to the
current winding of the instrument to allow 'warm up'. After a suitable 'warm up' (8 to 10 seconds
minimum for the 811A) the pendulum switch is closed. The 811A will continue to power the
instrument until precisely 43200 VAS are furnished and then the 811A will remove power.
To Next Page
Loading...