MIL-HDBK-1005/9A
4.6.1.2
Use Limitations. Different types of measuring devices
are available for each application. The listed capacity of a
device includes most sizes and types of the device that are
available. The range is the useful turndown ratio of a
particular device.
4.6.1.3
Discrete Versus Analog Devices. Alarm functions and
many control functions require only the presence or absence of a
process variable input for their operation. For example, a sump
pump may start if the liquid level is above a certain point or a
tank heater may start if the temperature is below a selected
point. Control these functions by discrete devices such as flow
switches, temperature switches, level switches, and pressure
switches. If the actual status of the process variable is
required, rather than on/off for indication or control, an
analog primary device should be used. Some alarm switches are
not included in the tables; for example, clarifier torque
switches, speed switches, and other equipment protection
switches that are normally supplied with the equipment.
4.6.1.4
Special Considerations. Primary measuring devices for
wastewater systems must meet more rigorous operational
requirements than those for water supply systems. Select
devices constructed of materials impervious to the corrosive
effects of the wastewater. Consider plugging of impulse or
sampling lines and buildup of solids and grease on analytical
probes when specifying these devices.
4.6.1.5
Ship Sewage. In the design of pier sewage collection
systems to receive sewage from ships, facilities to meter the
total flow through the collection system should be included.
The designer should consult the activity's Public Works
Department for metering needs. The location of meters necessary
to provide the needed information will be determined by the
layout of the collection system, but in no case should this
exceed one meter at the shore end of each pier. There is no
necessity to meter the flow from individual ships.
4.6.2
Instrumentation. Instrumentation covers all secondary
instruments (such as gages, indicators, recorders, or
totalizers) needed for efficient operation of wastewater
treatment systems. Information sensed by a primary device is
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