Technical reference and worked-example guide
Strain gauge and load cell PLC guide: field reference
Direct answer
The learner can distinguish the sensing bridge from the load-cell assembly and transmitter, scale a known load and diagnose zero, span, wiring and mechanical errors.
Written for instrumentation and PLC learners connecting strain-gauge bridges, load cells, weighing transmitters and analog values to reliable engineering units.
Definition
The force range, load-cell type, mV/V rating, excitation, bridge wiring, transmitter, analog interface, resolution and units.
Signal path
Mechanical load through strain, bridge imbalance, conditioned signal, PLC raw value, scaling and process decision.
Worked example
Zero, midpoint and full-scale known loads producing repeatable engineering values.
Limits
Off-center load, creep, temperature, overload, cable resistance, sense wires, noise and power return.
Common mistake
A mechanical, bridge, excitation, cable, transmitter, input-mode, zero or span fault.
Verification
The installation inspected and calibrated with approved weights, documentation and target input hardware.
What is the difference between a strain gauge and a load cell?
A strain gauge is the resistive sensing element. A load cell is a mechanical force transducer that normally uses several gauges in a bridge and often needs signal conditioning.
Can a load cell connect directly to a PLC analog input?
A millivolt bridge usually needs a compatible weighing module or transmitter. A standard voltage or 4–20 mA input cannot be assumed to accept the raw bridge signal.
How do you scale a load cell in a PLC?
Record zero and known-load raw values, calculate slope and offset in the chosen engineering units, then verify multiple points and fault ranges.