DONUT LOAD CELL WORKING PRINCIPLE & APPLICATIONS
How does a donut load cell work?
Axial compression enters a defined annular loading surface around a center bore. Strain gauges sense the elastic deformation and a bridge circuit produces a small electrical signal proportional to force within the calibrated range.
Keep the axial force in the supported annulus.
The center bore is a clearance or mounting feature, depending on the design. It does not mean the shaft itself should bear against the sensing body. Check the loading-ring diameter, support diameter and installed stack.
Off-axis force, uneven surfaces and installation torque can change the zero or produce errors. A matched pair of hardened loading washers can help establish a suitable contact interface when specified for the sensor and fixture.
Review locating threads and stud mounts →A 2 mV/V example is a signal calculation, not a DLC rating.
Illustrative bridge calculation: 10 V excitation × 2 mV/V rated sensitivity = 20 mV at full scale. At half of the calibrated force range, the ideal signal change is 10 mV before zero offset and other errors.
The selected sensor datasheet establishes the real sensitivity, excitation, polarity and uncertainty. Check amplifier input span and acquisition bandwidth separately.
Select a paired amplifier or digital readout →Choose the force path for the actual test.
Donut Load Cells for Die Clamping
Review compression force per clamping point, installed height and transient peaks in stamping die fixtures.
Review fixture inputs →Donut Load Cells for Injection Molding Fixtures
Scope direct axial force measurement in an injection-molding fixture with limited stack height.
Review fixture inputs →Donut Load Cells for Hydraulic Jack Testing
Evaluate axial jack thrust measurement around a central shaft or fixture stud.
Review fixture inputs →Donut Load Cells for Fastener Preload Testing
Measure axial clamp force during bolted-joint and aerospace assembly-tool evaluation.
Review fixture inputs →Specify lbf and inches without losing the metric context.
1 lbf = 4.4482216152605 N; 1 in = 25.4 mm. A 25,000 lbf request is approximately 111.206 kN. Force labels such as lbf and kgf should not be confused with mass-only lb or kg labels on a display.
Match range, ID, OD, height, mounting and the signal chain, then define the calibration points and fixture acceptance before procurement.