Rice Lake Combination System - Precision Loads On-Board Weighing Systems - Manual (Page 56)

52 Precision Loads On-Board Weighing Installation & Service Manual
Another method for isolation involves the use of a load simulator (a test device you can purchase from Rice Lake
Weighing Systems). When a bad test number is suspected, go to that transmitter lead, disconnect it from the load
cell/pin/transducer, and connect the simulator to the transmitter lead. If the indicator responds correctly to the
simulator, then the problem is usually with the load cell/pin/transducer.
Sometimes when testing a single channel system with three, four or six-lead transmitters, it may be necessary to
disconnect one lead at a time to observe changes in the display. When doing this, always reconnect the lead
disconnected before moving to the next lead if no problem is found.
Note
A disconnected lead will usually give a test number of 65000+ count range.
5.5.4 Calibration
Some of the system problems identified above are related to calibration. For example, system accuracy problems
which are small errors, or "always-high"/"always-low" errors are usually calibration-related. Recalibrating the
system is recommended. Also, whenever any major component of a system is replaced (load cell, transmitter,
indicator), re-calibration should be performed.
Other Issues to Consider
Intermittent errors can often be traced back to cable issues. If this is happening, note any error message on the
LCD. The cable between the transmitter and indicator is usually the most vulnerable and should be visually
inspected for breaks, cracks, pinches or flattened spots.
Other problems can occur only at certain load levels. This is typically due to a load cell "bottoming out" under load,
in which its deflection is restricted. This is rare, but if it occurs, inspection of all load cells and load cell bolts is
required. For load cells with single piece bearing plates and kingpin load cells, make sure there has been no
build-up of debris between the load cell and the slot of the bearing plates which can restrict normal load cell
deflection.
Stability and accuracy of the scale can be affected by the powering of other truck equipment which draws power
from the scale. If this occurs, check the power wiring to the scale to isolate it from other powered equipment such
as PTO's, pumps, crane's etc.
Note
The power cable must be connected directly to the batteries. Do not connect scale power to an accessory
terminal on the ignition switch, fuse panel, or behind the dash. The scale must have a CLEAN 12V source.
Check for error sources due to weight transfer around (not through) the load cells. Non-flexible tubing or piping, or
other attachments which transmit load or force which the load cells cannot measure must be avoided or remedied
(with flex joints) to prevent system errors. Also, installations in which the possibility exists for a cantilevering
effect between front and rear load cells (such an extended heavy pumping station) can cause non-linear weighing to
occur at lighter loads. In cases of extreme end loading, the load cells must be mounted as far forward or rearward as
possible between body and chassis to prevent any possible cantilever effects.
5.6 Cal Factors
Recording the Cal Factor (found in the Set-Up Mode) for each channel calibrated, after calibration is completed,
allows you to have an important reference for checking problems later. Also, if you ever change meters, you can
enter cal factors into a new or replacement indicator to maintain the system calibration stored in the previous
indicator.
When looking for problems in a system, refer to the recorded Cal Factor values. Any major changes are a sign that
re-calibration may be required, OR a component has failed.
5.7 Application-Specific Service Notes
5.7.1 Spring-mounted Load Cells
When mounting coil springs to load cells, the installer or service person must ensure that spring-mounting bolts are
tightened so that springs are compressed by a minimum of 0.25 inch (7 mm). The installer must also be aware of
thread depth of the mounting bolts for springs. These bolts must be threaded into the load cell bolt holes to a
minimum depth which is equal to the diameter of the bolt. For example, a 3/4" bolt must be screwed into the load
cell to a depth of 0.75 inch (19 mm). A serviceable thread locking material is recommended for spring-bolt
installations.