PCB Load & Torque, Inc.
Toll-Free in USA 866-684-7107
716-684-0001
www.pcbloadtorque.com
S-TYPE LOAD CELL OPERATION MANUAL
3
5.1 Electrical Drawing / Western Regional Std.
All load cells are wired following the Western Region
Standard. All models utilize strain gages configured into a
Wheatstone Bridge Circuit to produce the primary sensing
element. The four-arm Wheatstone bridge configuration is
shown below in Figure 3.
The gages are bonded to the load cell's structure.
Typically, a regulated DC or AC excitation is applied
between A and D of the bridge. When a force is applied to
the load cell, the Wheatstone bridge becomes unbalanced,
causing an output voltage between B and C, which is
proportional to the applied load. This configuration allows
for temperature and pressure compensation, as well as
cancellation of signals caused by forces not directly
applied to the axis of the applied load. Output is typically
expressed in units of mV/V of excitation.
5.2 Output Polarity
The following figure describes the output polarity.
5.3 Cable & Grounding Considerations
Proper grounding and shielding is required to prevent
electrical noise in strain gage load cell measuring systems.
The cable must be shielded twisted pairs with a drain wire.
Cable shields must be grounded only at one end, for example,
on the instrument or control system ground. The load cell
case is grounded by mechanical attachment to the structure to
which it is mounted.
The instrument or control system is grounded through its
power cord. Ground loops and measuring system wiring may
result in unstable or noisy signals.
A simple test with a voltmeter connected between the power
cord ground and the structure on which the load cell is
mounted can confirm that the structure has been properly
grounded. If the power cord ground and structure ground are
not at the same potential, it may be necessary to provide a
secure structure ground, perhaps by driving a copper rod and
attaching a ground strap.
6.0 CALIBRATION
Every S-type load cell manufactured by PCB Load & Torque,
Inc. has been fully calibrated per ISO/IEC 17025 procedures,
and meets all published specifications. Each load cell will
come with a calibration certificate designated with matching
model and serial numbers. PCB Load & Torque also offers
calibration services on an on-going basis.
6.1 Calibration Certificate Description
Calibration reports supplied with S-type load cells contain
valuable information to assist the customer in use of the
equipment. A separate calibration report is provided for
tension and compression calibrations. Calibration procedures,
equipment, and reports comply with ISO/IEC 17025.
6.1.1 Measured Output
The applied load starting at zero is measured in five
increments to full scale. Output (mV/V) is measured at each
increment. The straight-line from zero to the full scale
measurement is compared to the measured readings at each
increment to calculate the error at each load increment. The
deviations (% Full Scale) corresponding to non-linearity at
each measurement increment are then calculated.
Figure 5
- Grounding
Test Rig Ground
Power Supply
Instrument Ground
Cable Shielding
Load Cell
C
A
D
B
- Signal White
- Excitation Black
+ Excitation Red
+ Signal Green
Figure 3 - Western Regional Strain Gage Committee Wiring Code
Figure 4
- Output Polarity
Tensile Load
= Positive
Tensile Load
= Positive
