the manufacturer.
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Electrical recording instruments shall be of the [direct-acting]
[null-balancing] type. Instrument switches shall be provided when shown or
required to select between different quantities to be recorded, and shall
comply with the preceding requirements for instrument switches, as
applicable.
2.7.8.1
Basic Requirements
Electrical recording instruments shall be of the semi-flush,
back-connected, dustproof, switchboard and inkless type. The case shall
have a black finish and shadowproof viewing windows [and, insofar as is
practicable, shall be of the same size, style, and appearance]. The
driving motor shall be rated for 120-volt ac operation. Where ungrounded
input is required to an instrument, an isolating transformer shall be
provided. An instrument shall have a high visibility scale of a suitable
range, and indicating pointer, and an internal fluorescent light for chart
illumination. Chart speed shall be [20.8] [_____] micrometers/second [3]
[_____] inches/hour. An instrument shall be correctly calibrated for use
on the secondary of any instrument transformer to which it is connected and
shall have the indicated scale or a scale suitable for the application,
where a specific scale is not indicated. Necessary maintenance accessories
and a 6-month supply of charts shall be provided for each chart-recording
instrument. Chart length shall be sufficient to permit not less than 30
days of continuous operation at the normal chart speed without the need for
replacement.
2.7.8.2
Direct-Acting Type
Direct-acting type instruments shall be of the [single-channel,]
[two-channel,] strip-chart, self-contained, continuous-marking type with a
chart channel calibrated width of not less than 100 mm 4 inches.
2.7.8.3
Null-Balancing Type
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NOTE: The third and following sentences in this
paragraph should also be included in project
specifications when a direct-acting type of recorder
is to be specified.
**************************************************************************
Null-balancing type instruments shall be of strip-chart, self-contained,
direct-current potentiometer, periodic-marking type provided with an
associated and coordinated transducer for conversion of the measured
alternating-current quantity to the direct-current input required for the
instrument. Charts shall have a calibrated width of not less than 225 mm 9
inches. An instrument shall be provided with an internal lamacoid legend
plate suitably engraved, a chart supply indicator, a chart tear-off without
indices, a rubber chart identification stamp reading the same as the legend
plate, a chart reroll, a writing table, and an electric power "ON-OFF"
switch. The chart reroll shall be self-aligning, smooth in operation,
self-contained in the instrument case, and accessible for the changing of
chart rolls. The writing table shall be located under the uncovered part
of the chart between the indicator and reroll in such manner as to permit
convenient writing on the chart by merely opening the front hinged cover,
and shall be designed so that it will not interfere with replacement of
SECTION 16311A
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