Scale factors are expressed in basic units (e.g. Watt Hours per Pulse)
and should be set up not to exceed 20 pulses per second, the limit of the
933A. To arrive at the minimum scale factor value so not to exceed this
threshold, take the maximum value of the basic unit being measured and
divide by 72,000. This should give you the absolute limit (minimum value)
for a scale factor.
For example, if the maximum input value (including CT-PT ratios) is 240
kWh, then the minimum scale factor for Watt Hours should be greater
than 3.3333333 (240
,
000
÷
72
,
000 = 3
.
333
. . .
). The value produced is the
Scale Factor (e.g. 3.3333 Wh per pulse). Scale Factors will be directly
proportional to the value measured. Therefore, the greater the measured
value, the greater will be the minimum Scale Factor.
Over-Range Condition
: An over range input condition will exceed the
20/second output capability of the 933A, causing KYZ pulses to stabilize
at that rate. If this is the case, for momentary periods, the accumulator
in the 933A will store these counts not degrade the Model 933A accuracy.
If data has accumulated in the 933A, then when the signal has dropped
below 100% (by Scale Factor) the output will put out the additional pulses
until the accumulated overage equals zero.
Relays 2 and 3, Mechanical Contacts
Relays 2 and 3 are two separate mechanical contact sets and each have a
limited lifetime of about 100,000 cycles. Contacts are designed to change
state based on the configured Trigger for each relay. For example, Relay
2, in the Figure 7.16, is set to trigger based on the state of Trigger 2.
When the trigger limit condition is exceeded, then the trigger is considered
Active and the relay will change state. When Trigger 2 changes back to
the previous state, then the relay will revert to its previous state. Relay 3
is identical to Relay 2 and can be set up in the same manner as Relay 2.
As seen in Figure 7.17, Trigger 2 is responsible for activating Relay 2 when
A-phase voltage drops below 85.0 Vrms. Notice that a hysteresis value of
2.00 was used to reduce the chatter from a signal on the measured channel
fluctuating above and below the limit value.
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