Rice Lake JB1010 Signal/Excitation Trim - Manual (Page 11)

8
8.0 Using the JB1010 In an Existing System
Large vehicle scales often have two, three, or four junction boxes connected into a network. When servicing
these scales, you don’t have a choice of what’s going to fail. When one of the junction boxes fails, it shuts the
whole scale down. The service technician rarely has the right board with him to replace a third party junction
board. As a universal board, the JB1010 can usually serve as a replacement.
The JB1010 can be adapted to match almost any common (and some uncommon) summing boards. To do this,
you can study the old board, look for isolation resistors, and see how the trimming works. Sometimes, however,
you have to make an intelligent guess.
Most large trimming boards use signal trim. If you see a large number of resistors on the circuit board, it is a good
bet that the board is a signal trim board. Most signal trim boards either have 2.5KΩ or 1KΩ isolation resistors.
If the board has both individual cell and section trimming, then there are often two sets of isolation resistors.
Use the following strategy to identify and match existing trim boards:
1. Are there many resistors on the existing board? If so, what is the value of the ones most prevalent on
the board. These are almost always the isolation resistors. If you can’t read the value, guess 2.5KΩ.
2. Are there any adjustment potentiometers for individual cells? Are there any adjustment po ten ti om e ters
for sections? Are there both? If there is only a single set of potentiometers, then use the value of the
isolation resistors. Guess 2.5KΩ if you aren’t sure. If there are both individual and section trimpots,
then choose the double isolation examples shown Section 7.0.
3. If you can’t fi nd any isolation resistors, set up the board to disable trimming. Read on to tell if the trim
you have selected is correct. Disable any unused channels.
4. If the junction box you are replacing has an expansion port, use any unused cell (disable trim on it fi rst)
as the expansion output.
In any case, power up the system and see if the indicator appears to work. If you get stable numbers, you are
on the right track.
If you are using signal trimming, you can tell if the isolation resistors match by the output of the cells. Put a
weight on cells connected to the existing box and record the value. Put the same weight on a cell connected
to the JB1010. If the reading is nearly the same, then the isolation resistor setting is probably correct. If the
weight from the JB1010 is much too high, then the isolation resistors you have chosen are too low for the rest
of the system or the system may have two layers of isolation resistors. If the weight from the JB1010 is much
too low, then the isolation resistors you have chosen are too high for the rest of the system. You must match
the isolation resistors as closely as possible so that the cell outputs are nearly the same. Once this matching is
done, then trim the total system like any other scale.