11.4.2 FWD/HWD Control Circuits
The remaining electrical circuits of the FWD/HWD unit are exclusively used for operational
control, powered via the 12V trailer buffer battery.
The Compact15 front panel incorporates 4 pushbuttons for manual operation of the FWD/HWD
unit, and 6 LEDs for monitoring of the trailer proximity- and pressure switches.
11.4.3 Trailer Status Switches
Two pressure sensitive switches, placed as indicated in the previous descriptions of the
hydraulics, and four proximity switches, placed as indicated in figures in the following, are used
for detection of the trailer “status” and are monitored by 6 LED indicators of the Compact15
Front Panel, close by their respective connection sockets.
P1: A pressure sensitive switch with a normally closed contact that opens when the pump
outlet pressure exceeds its setting of approx.
FWD: 40 bar (560 psi)
HWD: 60 bar (850 psi)
P1 is used for excess pressure detection. Thus, the (red) P1 LED must turn OFF at
excess pressure.
P2: A pressure sensitive switch with a normally open contact that will close by the pressure in
the RETURN oil during catch lowering (setting approx. 2 bar (25-30 psi). P2 MUST stay
ON WHILE the catch is MOVING DOWNwards, and it MUST come OFF when the
catch stops at its bottom position.
PH: “Plate High” proximity switch sensor, only activated when the plate (i.e. the falling weight
subassembly) is close to its highest position. Thus, the PH LED must be ON when the
plate is high. It must also be ON when the subassy is resting on the transport locks in
EITHER or BOTH side(s).
WH: “Weight High” proximity switch sensor, activated by close presence of any of the falling
height stops (located in a rail on the drop weight). Thus, the WH LED must turn ON at
each passing of a falling height stop.
PL: “Plate Low” proximity switch sensor, which is DEactivated, when the falling weight
subassembly is no longer suspended from the two shafts of the side cylinders. This is
normally only the case, when the plate has come to rest on the ground, but may occur, if
the subassembly should for some reason be prevented from being lowered (e.g. if the
transport locks have not been unlocked). Thus, the PL LED must turn OFF when the
plate is low.
TG: “Trigger” proximity switch sensor, activated when the drop weight is less than 6 to 12 mm
(1/4” to ½”) from its lower, resting position. Thus, the TG LED must be ON when the
weight is low AND it must turn OFF when the weight has been raised more than 6 to
12 mm (1/4” to ½”).
The four proximity switch sensors and the pressure switches are connected to individual sockets
of the Compact15 Front Panel.
On activation, the output of a proximity sensor is pulled low (by an internal, current limited
NPN-transistor) to max. some 1V from the PWR GND, which must cause the corresponding
LED indicator to turn ON.
Test procedures for these status sensors are given in 16.10, “Checking the four Proximity Switch
Sensors” and 16.11, “Checking the Pressure Switches”.
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