Salter Brecknell 7550 - Manual (Page 5)

The scale component of the conveyor scale is suspended by means of
chains from four Weigh Bars.
® The Weigh Bar outputs feed into a junction
box which is connected to the scale indicator by an interface cable. The
chain link suspension of the belt assembly allows some movement, thus
helping to absorb the adverse effects of vibration or jolts. The scale also has
four overload stops that help prevent damage to the Weigh Bars.
The conveyor scale has two NEMA IV rated photoelectric eyes, and two
reflectors—one at each end of the scale. When the product to be weighed
enters the scale, it breaks the beam of the first photocell. As soon as the
product clears the first photocell, the indicator starts recording weight
readings until the product breaks the beam of the second photocell. Once
the second beam is broken, the indicator averages the recorded weights
and transmits this average to the computer. This weight averaging tech-
nique results in much more accurate weighments. Weigh-Tronix conveyor
scales are accurate to within ±.1% of scale capacity provided the entire
item being weighed remains on the scale for at least one second.
Lift each corner of the belt assembly and remove the shipping material
under each overload stop. The following recommendations will prevent
problems which can affect weighing performance. They are not intended to
replace or suggest that local or national electrical codes be ignored or
deviated from.
Orientation – The conveyor belt must travel in the right direction for the
conveyor scale to function properly. Be sure the belt moves towards
the end where the electric motor is located. If not, the belt will be
pushed rather than pulled which causes the belt to run less smoothly,
noisier, and will reduce the weighing accuracy achievable by the conveyor
scale system.
Height – The height of the conveyor should be adjusted such that the
conveyor height is the same as the entrance conveyor and the exit conveyor.
This should be done as accurately as possible to ensure as smooth a
transition as possible.
Motor Connections – The motor is part of the “live” part of the scale so
the electrical connection to the motor can have a significant impact on the
weighing performance. Avoid very short or very rigid connections.
Photocell Programming – The photocells used on the conveyor scale
have programming modules in them, and the entrance photocell is pro-
grammed differently than the exit photocell. The entrance photocell is
programmed to trigger only after the back edge of the item clears the
entrance photocell. The exit photocell is programmed to trigger as soon as
Features
Installation
Recommendations
Installing the Conveyor Scale
2