MIL-HDBK-1005/7A
6.13.4.2 Transmission . Refer to AWWA Manual M2, Automation and
Instrumentation, for information regarding pneumatic and
electrical controls. 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 ft. Reaction time of pneumatic loops is relatively long
if transmission distance is long.
d) Electrical. There is no limitation on distance.
Analog signals may require amplification for transmission
distances greater than 1,000 ft.
6.13.4.3 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).
6.13.5
Controls. Refer to Water Treatment Plant Design,
Chapter 20, "Process Instrumentation and Controls," AWWA, third
edition; and AWWA Manual M2, Automation and Instrumentation.
Controller devices are needed to regulate the functions of
equipment throughout the process. Consider automatic controls
where significant improvement in performance will result, or
where cost can be offset by reduced operating manpower needs.
Otherwise, keep controls as simple as possible. Wherever
feasible, use fixed or manual controls (for example, weirs,
launders, siphons, or throttling valves) in preference to
mechanical devices, and direct acting controls (for example,
float valves) in preference to electrically or pneumatically
actuated devices. Always consider effects of possible control
malfunctions. Controls may be classified by the degree of
automation (see Table 14).
6.13.5.1 Manual. Use manual control where the operator will
start, stop, or adjust rates of operations based on instrument
observations, laboratory tests, or indicated conditions.
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