GENERAL INFORMATION
Most industriai load cells are used in multiple load cell weighing systems. Load
cells should be electrically connected in such a way that the signal (output) lines,
excitation (power supply) and sense (when present) lines are in parallel.
Usually the connection is not made at the signal conditioning device, but in a
separate housing, a so called junction box, located adjacent to the weighing
system.
4 WIRE / 6 WIRE LOAD CELLS
A load cell may have a cable with four or six wire. A six-wire cable, besides
having +/- excitation and +/- signal lines also has + and - sense lines. lt is a
common misconception that the possibility to sense the actual voltage at the load
cell is the only difference between 4-wire and 6-wire load cells.
A load cell is compensated to perform within specifications over a certain
temperature range (usually -1 O - + 40 °C). Since cable resistance is a function of
temperature, the cable response to temperature-changes must be eliminated.
The 4-wire cable is part of the temperature compensating system of the load cell.
The load cell is calibrated and compensated with a certain amount of cable
attached.
Never cut a 4-wire load cell cab le.
The 6-wire cable is not part of the temperature compensating system of the load
cell. The sense lines are connected to the sense terminals of the signal
conditioning device, to feed back the actual voltage at the load cells. The signal
conditioning device either adjusts its output voltage or adjusts its amplifier to
compensate for any resistance change in the cable. The advantage of using this
"active" system is the possibility to cut (or extend) the 6-wire load cell cable to
any length.
A 6-wire load cell will not perform within specifications if the
sense lines are not used.
ELECTRICAL CONNECTIONS
The following figures represent the two basic configurations, using four- or six
wire (sense) load cells and Z-SG as signal conditioning device (measurer). With
4-wire extension cables the load cell output should be connected to pairs of
diagonally apposite wire.
Sometimes it is necessary to trim the output of each individuai load cell to avoid
corner load differences, which are caused by:
1) The parallel connection. Each load cell will be loaded with the resistance of the
other load cells. As a result, the individuai load cell output tolerances will be
increased by the individuai output resistance tolerance.
2) Unequal load distribuition.
ENGLISH - 2/7
MI00155-3-EN
Summary of Contents for SG-EQ4
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