of NEMA Type 7, Class I, Division I, Groups C and D, and NEMA Type 9, Class
II, Division I, Groups E, F, and G.
2.9.18.1
Type A - Diaphragm Type Presence Indicator
Pressure-sensitive to presence of coal consisting of housing, diaphragm,
limit switches, wiring, and mounting bracket flanges. Housing shall be
either cast iron, stainless steel, or protected cast aluminum, with
synthetic diaphragm as recommended for coarse slightly abrasive materials.
Diaphragm deflection shall actuate a limit switch to indicate coal
presence. Design unit so that maintenance, diaphragm replacement and
sensitivity adjustment can be made from outside the bin. Type and number
of contacts and voltages shall be as indicated on control diagrams.
2.9.18.2
Type B - Paddle Type Presence Indicator
Paddle mounted on a counterweighted horizontal shaft so that deflection of
paddle rotates a cam which actuates a limit switch in a control box mounted
on the shaft. Unit shall consist of paddle, shaft, enclosure, limit
switches, wiring, and mounting brackets. Shaft shall be cold rolled steel
and paddle shall be stainless steel with control enclosure of cast iron,
stainless steel, or suitably protected cast aluminum. Type and number of
contacts and voltages shall be as indicated on control diagram. Mount
shaft in ball bearings equipped with suitable dust seals and fittings for
pressure grease lubrication.
2.9.18.3
Type C - Tilt Type Presence Indicator
Conical steel float that shall be tilted by presence of coal. Unit shall
consist of housing, conical float, universal pivot-collar, pendant
mechanism, dust seal, limit switches, wiring, and mounting brackets. Unit
shall operate so that tilting of float actuates a limit switch in enclosed
housing above. Provide a hood constructed according to manufacturer's
recommendations for the indicator's location of not less than 5 mm 3/16 inch
thick steel plate. Provide access panel for servicing the unit. Tilt
type indicator may be a totally enclosed type in which tilting causes a
ball to roll off the center actuating a limit switch. Design unit to be
cable hung and to tilt on presence of coal. Type and number of contacts
and voltages shall be as indicated on control diagram.
2.9.18.4
Type D - Rotating Type Presence Indicator
Rotating paddle where presence of coal stalls motor and actuates a limit
switch. Unit shall have either cast iron or cast aluminum housing,
stainless steel paddle, couplings, and flexible shaft. Shaft seal shall be
spring loaded and shall prevent buildup of fines between shaft and hub.
Operation shall be such that when paddle stalls motor continues to operate
until limit switch is actuated, which in turn shuts off current to motor.
Vane and baffle arrangements shall be according to manufacturer's
recommendations for each indicator location. Type and number of contacts
and voltages shall be as indicated on control diagrams.
2.9.18.5
Type E - Vibrating Type Presence Indicator
Vibrating sensing rod so that presence of coal dampens vibrations actuating
a control signal. Sensing rod shall be stainless steel not less than 10 mm
3/8 inch in diameter. Control unit shall be solid state, with type and
number of contacts and voltages as indicated on control diagrams.
SECTION 15501N
Page 89
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