MTS Model 506-62-72 Hydraulic Power Supply - Manual (Page 39)

Theory of Operation 5-5
5 . 2 . 2 Interlocks
The HPS contains interlock circuitry to shut down the HPS when
various conditions occur—such as low level hydraulic fluid, over-
temperature, low pressure, dirty filters and motor overload.
Reset When the interlock condition has been corrected and the HPS is
restarted, Reset switch 2PB at PLC input 006 must be pressed to reset
the interlock circuitry.
Low-level hydraulic fluid Low fluid level switch 1FS protects the HPS if there is an appreciable
loss of hydraulic fluid. Whenever the level of hydraulic fluid in the
HPS reservoir drops below a preset limit, switch 1FS (at PLC input 007)
opens to turn off the pump motor, and disable the supercharge pump if it
is in the Start/Run mode. PLC output 100 generates the interlock. PLC
output 108 lights the Low Fluid Level indicator on the HPS front panel.
Fluid over-temperature
condition Whenever the temperature of the hydraulic fluid in the HPS reservoir
exceeds a preset limit, switch 1TAS (at PLC input 008) opens to turn off
the HPS pump motor. The supercharge pump can be operated in the
Start/Run
mode to cool the fluid. PLC output 101 generates the
interlock. PLC output 109 lights the Fluid Over-Temperature indicator
on the HPS front panel.
Low-inlet pressure Pressure switch 1PS protects the main pump if inlet pressure drops
below the minimum level required by the main pumps. Switch 1PS (at
PLC input 012) closes whenever low-inlet pressure drops below a preset
limit (typically 50 psi). Closing 1PS while the pump motor is
operating, turns off the HPS. The supercharge pump, however, can be
operated in the Start/Run mode.
Water control valve
temperature switch Whenever the temperature of the hydraulic fluid exceeds a preset
limit, switch 2TAS (at PLC input 000) opens to energize water-inlet
solenoid 2SOL (at PLC output 107). This solenoid controls the water
valve allowing water into the heat exchanger to cool the hydraulic
fluid.
Dirty filter The low-pressure fine filter is monitored by
∆
P switch 2PS (at PLC
input 001). When a dirty filter creates excessive differential pressure
across the filter, switch 2PS opens. PLC output 102 generates the
interlock. PLC output 110 lights the Dirty Filter indicator on the HPS
front panel. If the indicator is active when the HPS shutdowns, Reset
must be pressed (after the filter is replaced) to restart the HPS.
Motor overload Thermal overload sensors detect excessive current and open the
normally closed contacts connected to the motor starter coil. Motor
overload relay contacts 1OL and 2OL at PLC input 009 open to turn off
the HPS off if the supercharge or main pump motor draws excessive
current. When an overload condition occurs, the reset button on the
motor overload relay must be pressed (see Subsection 3.3.1).