On demand, the computer prints a complete analysis of the system and output
totals to present. When strategically located meters are connected to a
computerized system with critical parameters, the computer can instantaneously
provide the information necessary to monitor, control or operate a system.
1.5 Demand Billing. As the cost of energy, materials, and labor increases,
there is a need to limit the large, intermittent demands on systems and to
encourage utilization during offpeak periods. To accomplish this task and
identify systems not in conformity with policy, instrumentation is required.
1.5.1 Control Parameters. Control parameters depend on the characteristics
of the system. Some systems are limited in peak capacity and q ust control
maximum use. There may be other areas of concern that are unique to a
particular system, such as a user who intermittently uses power at a rate that
overloads the system, affecting many other users.
1.5.2 Recorder Types. Common instruments used in a demand billing system are
a rate recorder such as the one illustrated in Figure 10-2, or a circular
recorder, as shown in Figure 10-9. Circular recorders are not highly
effective if data reduction is required and have been replaced with a data
logger with reduction by microprocessor program. These devices record the use
rate continuously. Peaks are easily detected over the period of recording.
If a recorder is used, the preferred type is a linear tracking, multichannel
recorder. One advantage of this system is that the chart becomes a permanent
record in case of customer disagreement concerning subsequent billings.
1.5.3 Alarm Actuator. A unique variation of chart recorders is shown in
Figure 10-10. In this application the utility installs an instrument with a
recorder onto user equipment. The agreement with the user is that severe
penalties will be levied each time the use exceeds a predetermined rate. In
an effort to avoid the penalty, a two-point alarm actuator is installed with
an alarm programmed to respond at some warning point before the limit is
reached, and then to initiate action if the limit is exceeded.
1.5.4 Alarm With Totalizer. Another variation of a use rate and penalty
system is shown in Figure 10-11. This approach places a penalty (generally a
unit price increase) on all consumption exceeding the limit. This is
accomplished by employing an alarm actuator and using a totalizer to record
the excessive usage.
2.1 Meter Energy Usage. Although each medium requires a specific type of
meter, all meters must have a signal-generating device to provide either
onsite or remote data reading and recording capabilities. The meter q ust
sample the media and transmit a representative signal to the system. Electric
meters rely on the medium they monitor for energy to produce the monitoring
signal. Turbine meters generate their own signal. Many meters rely on an
outside source of electricity to produce a transmission signal.