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 The pointer-indicating type frequency meter is connected directly across the line or the secondary
of one phase of a potential transformer. A frequency meter may have a scale range such as 55 to
65 Hz or 58 to 62 Hz for use on a 60 Hz system, and the moving pointer indicates the exact
value.
5.2.7 Portable Instruments. Most instruments are permanently mounted on switchboards, but
many can be obtained in portable forms. Portable instruments are useful for special tests or for
augmenting permanent instruments. Provisions are sometimes made on the secondaries of
instrument transformers for connecting portable instruments into the circuit. Portable current and
potential transformers are available when the self-contained range of the portable instrument is
not sufficient for the values to be measured.
Examples of typical portable instruments are portable ammeters, voltmeters, and wattmeters.
These may be of the indicating or recording type depending on the type of test or data required.
A versatile alternating current portable instrument, sometimes called a circuit analyzer, is
available to read current, voltage, and resistance. The circuit analyzer may operate on either
alternating or direct current, therefore, providing flexible instrumentation for various conditions.
5.2.8 Recording Instruments. Most instruments available as direct-reading indicating
instruments are also available as recording or curve-drawing instruments. A continuous record
of current, voltage, power, and frequency may be required for economic, statistical, and
engineering studies, as well as for checking operator and machine performance. The record is
traced automatically on either a strip or a circular chart by a pen fastened to the end of the pointer
of the instrument. The chart is moved at a constant speed by a clock mechanism. Some
recording instruments have adjustable speeds for movement of the chart. Normal records are
obtained at a speed consistent with chart-changing schedules, types, and load characteristics.
Special tests may require a more rapid chart speed in order to obtain proper data. These special
tests may require more sophisticated equipment, such as magnetic tape recorders.
5.2.9 Miscellaneous Instruments
5.2.9.1 Temperature Indicator. Temperature indicating and temperature control devices
include liquid, gas, or saturated-vapor thermometers, resistance thermometers, bimetal
thermometers, radiation pyrometers, and thermoelectric pyrometers. These devices may be
obtained as indicating instruments or as recorders. They are used for measuring temperatures of
electric windings, bearings, oil, air, and conductors. Some of them can be obtained with electric
contacts for use on an alarm device or relay circuit. Pyrometers are generally used for indication
and control of furnace temperatures.
5.2.9.2 Megohmmeter. A megohmmeter is an instrument for measuring the insulation
resistance of electric cables, insulators, buses, motors, and other electric equipment. The
megohmmeter consists of either a hand- or motor-driven direct current generator and resistance
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