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 CHAPTER 10.
INSTRUMENTATION IN METERING
1. DESCRIPTION. Today's versatile electronic instrumentation allows managers
to manage their systems 24 hours a day without using meter readers. The old
method of collecting data using meter readers, who periodically inspect and
log readings for strategic meters, creates a reaction delay to situations that
should be corrected immediately. For instance, in the event of a line break,
modern instrumentation would report the leakage upon occurrence as opposed to
later discovery by a meter reader. An instrument alerts the operator that an
excessive flow is passing through the system and the manager can then take
immediate action. The meter can record the time and magnitude of the leakage,
actuate alarm systems, and provide a variety of signals to initiate corrective
action. In addition to providing-information on occurring events, electronic
instrumentation provides records for later viewing to analyze trends or
significant changes or billing information.
1.1 Operating Principles. An electronic instrument records the amount of a
media passing through a meter and converts it into an electrical signal to be
displayed in meaningful units. Other equipment can be controlled based on
this signal. Consumption registered on an electromechanical or electronic
totalizer shows the amount of the media that has passed through the meter over
a period of time. Quantity may be displayed in a variety of units, not
necessarily those displayed on the meter register. A second common instrument
display is the instantaneous rate through the meter.
1.1.1 Meter Output. The output is typically shown on an analog (a needle and
scale instantaneous reading meter) or digital (a digital readout meter
reporting in discrete scale increments) indicator. Output may also be fed to
a variety of chart recorders for permanent records.
1.1.2 Meter Signals. Along with the basic outputs, modern processors are
able to provide a variety of signals for use with computers and other process
management equipment. Some examples of output signals are: 4-20 mA, 2-10
VDC, O-5 VDC, and 3-30 VDC pulse. If the data is to be entered into a
computer system, an interfacing module can prepare the data signal for an
RS-232C input application. These signals offer an infinite variety of system
control functions and can provide data readouts to both local and remote
locations. The receiving equipment is able to convert the data received from
a simple slave device into a base for a complete management system.
1.2 Local Instrumentation. Figure 10-1 shows a meter sending an electronic
signal to a local instrument that displays the instantaneous use rate on an
analog indicator and the total use measured on a totalizer. The analog use
rate indicator may be replaced with a digital indicator or a variety of
recording devices, if desired.
1.2.1 Meter With Onsite Recorder. Figure 10-2 shows an equivalent package
with a 31-day strip chart recorder that replaces the analog indicator of the
system in Figure 10-1. This configuration is used when data is required at
10-1
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