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State of California, Department of Transportation - page 29 / 52

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The AC plant

inspector

must

understand how

the batch

plant

controller

operates.

There

are

many different types of controllers, but the function is basically the same. If the plant inspector is unfamiliar with a specific controller, the District Weights and Measures Coordinator should be able to answer your questions. Manuals for the batch controller are located at the plant site and available to the inspector at all times. The manuals will probably contain the answers to a majority of

Notice the lights on this display, they visually indicate the status of each weighing cycle when inspecting the interlock tolerance settings. Instructions for checking these settings shall be made available at the plant.

your questions. Also, the controller manufacturer may be called upon to answer any

questions not addressed in their manual. when inspecting an AC batch plant:

Some other important questions to ask yourself

Q - Are the batching device interlocks functional?

A - A new batch may not be started until all weigh hoppers are empty, the scales are at zero, and the discharge gates are closed. Caltrans requires all AC batch plants to provide a means to check and verify the over-under tolerances.

Q - Are the aggregate hot bins and the aggregate weigh hopper interlocks functional?

A - No more than one bin may be discharged onto any given scale at one time, and the weigh hopper gates cannot be opened until the required quantity from each bin has been deposited onto the weighing device.

Q - Are the zero tolerance interlocks set correctly and functional?

A - "Zero tolerance" refers to the aggregate and asphalt scales returning to zero before starting a new batch. The "zero tolerance" for aggregate scales is 0.5 percent of the total batch weight of the aggregate, (.005 X AGG). The "zero tolerance" for asphalt scales is 0.05 percent of the total batch weight of the aggregate (.0005 X AGG). The "zero tolerance" can be a plus or minus.

Q - Are the over-under tolerance interlocks set correctly and functional?

A - "Over-under tolerance" refers to the pre-selected weights set on the control panel for

each individual aggregate size and the liquid asphalt tolerance" for each individual aggregate size deposited in

weigh

pot.

The

"over-under

the weigh hopper is 1.0 percent

of the total batch weight of the aggregate (.01 X AGG). The liquid asphalt deposited in the weigh pot is 0.1 percent of aggregate (.001 X AGG). The "over-under tolerance" can be a

"over-under tolerance" the total batch weight plus or minus.

for of

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