Rice Lake JB8SPT TuffSeal Signal Trim Junction Box - Manual (Page 11)

Trimming Procedure 7
5.0 Trimming Procedure
Trimming is a process of equalizing the output from multiple individual load cells. If needed, load cell output can
be individually trimmed with potentiometers.
Whenever a substantial amount of trim (more than 7% of normal output), seems necessary to equalize output,
check for other possible problems. The best trim is always the least amount of trim.
The JB8SP and JB8SPT is a signal trimming device with individual and section trimming potentiometers (see
Figure 4-1 on page 5).
Use the following steps to properly trim the JB8SP and JB8SPT junction box.
Note: If using two junction boxes with an expansion cable between them, make sure you cut the sense trace on the board that
has the home run cable connected to it (see figure 4-1 on page 5). This ensures sensing out to the furthest junction box within the
system. You must use sic conductor cable between the two junction boxes to ensure proper functioning of sense.
1. Determine the number of load cells needed. It should be noted that when section trimming you can use
combinations of load cells other than eight, but the combination must be an even number of cells.
2. Turn all the individual cell and section potentiometers that you are using fully CLOCKWISE to give
maximum signal output from each section. Make sure you remove all shunt jumpers of the individual
cells you are not using to disable them and ensure the section potentiometer for these is turned fully.
Note that if desired, all the potentiometers can be adjusted 3-5 turns counter-clockwise to allow trim
capabilities both positive and negative.
3. Trim by turning potentiometers COUNTER CLOCKWISE to lower output to match lowest value.
4. Remove all weight from the scale and zero the indicator. Place calibrated test weights over each load cell
or section. The amount of test weights to be used will depend on the scale configuration; for specific
recommendations, refer to the Handbook 44, published by the National Institute of Standards and
Technology (NIST).
5. Record the value displayed on the indicator after the test weight is placed in turn over each load cell, or
over each section. Select the load cell or section that has the lowest value as your reference point. This
cell or section will not be trimmed.
6. Place the same test load over each cell or section in turn. Using the corresponding potentiometer trim
each cell or section down to equal the reference point. As load cell corrections are interactive, check zero
after every adjustment to avoid zero shift. Also check cells or sections again and repeat steps six, seven,
and eight as needed.