MIL-HDBK-1005/9A
translated by instruments into an operator usable form called
"readout." Most analog primary devices require secondary
instruments, although a few (such as displacement meters)
contain built-in counters.
4.6.2.1
Use Limitations. Instruments may be obtained in any
combination of totalizing, indicating, or recording of
information developed by primary devices. Other more
sophisticated forms of instruments (such as summation and
multiplication of variables) are possible, but are not normally
needed.
4.6.2.2
Transmission. Select means of transmitting
information from primary measuring devices to secondary
instruments from the following:
a) Mechanical. Transmission distance is limited to a
few feet. Consider the effects of corrosion, wear, or icing on
b) Pneumatic. Transmission distance can be up to
1,000 feet (304.8 m). Reaction time of pneumatic loops is
relatively long if transmission distance is long.
c) Electrical. There is no limitation on distance.
Analog signals may require amplification for transmission
distances greater than 1,000 feet (304.8 m).
4.6.2.3
Remote Indication. Remote indicators should provide
the operator with the status of any function necessary for
remote operation of the plant. Panel lights should indicate the
on/off status of pumps or other discrete devices, alarm
functions, and operator-actuated functions (for example,
initiate backwash, fill day tank).
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