Reading
- pp. 29 - 34. Start reading at the beginning of the MOTOR
OVERHEAT section. Stop reading when you reach the Magnetic
Overload Relays section on p. 34.
- Unit 10 (p. 113)
Explanation of the schematic on p. 115
- Contactor
- The contactor turns the motor on and off. It has three pairs of contacts, each labeled M.
- In addition to the three pairs of contacts used to turn the motor ON and OFF, there is a fourth pair of contacts across the Start switch.
- All four pairs of M contacts are controlled by coil M.
- Each of the three wires going to the motor contain
overload heaters. These heaters heat up a trip mechanism that causes
overload contacts to open. These contacts are represented by the
normally-closed contacts to the right of the coil M. When these
contacts open, current to coil M is turned OFF.
- Control-relay PSCR (pressure-switch control relay).
- Coil PSCR controls two pairs of contacts, one normally open and one normally closed. These contacts are labeled PSCR.
Questions
- The bale and log pressure switches on the car crusher at
the recycling facility in Milan are of the type that have two
adjustments. One is for the pressure at which the switch closes. The
other is for adjusting the differential pressure. Give a short
definition of what the differential pressure adjustment is for.
- In the diagram on p. 115, what type of motor is used? Single phase or three phase.
- If the START button is pressed and then released,
will relay coil M be ON or OFF? (Assume that the PSCR and OL contacts
on the same line as coil M are in their closed positions.)
- If the OL heaters in the three wires going to the motor
heat up too much (indicating a motor overload), will coil M be ON or
OFF?
- If the pressure switch trips (indicating that the trip pressure has been reached), will coil M be ON or OFF?
- Also, when the pressure switch trips, will the warning light be ON or OFF?
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