A compression machine can appear to be operating normally while its force readings slowly move away from the true applied load. That is the practical risk behind the question, what causes load cell drift. In a concrete testing laboratory or industrial test environment, even a small, unmanaged error can affect reported results, compliance confidence and decisions made from those results.
Load cell drift is not one fault with one remedy. It is a change in the output of a load cell over time when the applied load is unchanged, or a gradual change in its sensitivity across the measurement range. Finding the cause requires separating normal, predictable behaviour from signs of damage, poor installation or an electrical problem.
What causes load cell drift?
A load cell converts strain in a metal element into an electrical signal through bonded strain gauges. The signal is very small, so it is influenced by the condition of the sensing element, the surrounding environment, the cable and connections, and the indicator or control system receiving the signal.
Drift may show as a changing zero reading with no load applied, a reading that rises or falls while a test load is held, or a growing difference between the displayed and known force during calibration. These symptoms matter, but they do not always point to the same root cause.
Temperature change and thermal effects
Temperature is one of the most common causes of apparent load cell drift. Both the load cell body and its strain gauges react to changes in temperature. Quality load cells include temperature compensation, but compensation has limits. A cold machine brought into a warm laboratory, direct sunlight on part of a test frame, or heat transferred from hydraulic equipment can all introduce a changing signal.
Temperature gradients are often more troublesome than a stable room temperature. If one side of a load cell warms faster than the other, the resulting strain can be interpreted as force. The reading may settle only after the equipment has reached thermal equilibrium.
This is why calibration and critical testing should be carried out in controlled conditions where practical. It is also sensible to allow the machine, load cell and electronics adequate warm-up time, particularly after transport, cold storage or a significant change in ambient temperature.
Creep and recovery under sustained load
When a force is held on a load cell, the output can change slightly even though the force itself has not changed. This is known as creep. After the load is removed, the output may take time to return towards zero, which is referred to as recovery.
A specified level of creep can be normal for a load cell, especially during long-duration loading. The concern is excessive creep, poor recovery or a change in behaviour compared with previous checks. In a testing machine, the effect can also come from the frame, platens, hydraulic system or fixture settling rather than the load cell alone.
A useful diagnostic is to apply a stable, traceable load and monitor both the load indication and the physical system. If hydraulic pressure is changing, a drifting display does not automatically prove that the load cell is at fault. Conversely, stable pressure does not prove the true force is stable. A suitable reference and a structured test are needed.
Overload, shock loading and mechanical damage
Load cells are designed for a stated capacity and loading direction. Exceeding that capacity, dropping a specimen or fixture onto the machine, or applying a sudden impact can permanently alter the strain element. The load cell may still produce plausible readings afterwards, but its zero balance, linearity or repeatability may have changed.
Mechanical damage is not limited to a clear overload event. Repeated operation close to capacity, frequent high-cycle use and poor test set-up can create cumulative problems. In compression testing equipment, poorly centred specimens, damaged bearing surfaces or incorrectly seated platens can introduce side loading and bending that a tension or compression load cell was not intended to carry.
Side loads, torsion and off-axis loading are particularly significant. They may cause inconsistent readings depending on specimen position, rather than a simple steady drift. Correct alignment and clean, undamaged loading surfaces are therefore part of measurement control, not merely good housekeeping.
Mounting stress, binding and misalignment
A load cell must be able to strain as intended. If its mounting arrangement is distorted, overtightened, corroded or obstructed, external stresses can enter the sensing element. Cable glands, stop blocks, pipework, guarding or accumulated debris can all create an unintended load path.
This issue is often missed after a repair, relocation or replacement of adjacent components. A machine may have calibrated acceptably before work was carried out, then develop unstable zero readings because the load cell is now being slightly restrained or preloaded.
The practical check is not simply whether all bolts are tight. The installation must follow the equipment design and load cell manufacturer’s requirements, with the force path centred and free from interference. Any mechanical inspection should be performed safely, with the machine isolated and supported as required.
Moisture, contamination and cable damage
Load cell cables and connectors operate at low signal levels. Moisture ingress, damaged insulation, contaminated connectors and deteriorated cable glands can create leakage paths or intermittent electrical resistance. These faults often become worse in damp conditions or after wash-down and may present as unstable readings, wandering zero or erratic changes when the cable is moved.
Concrete testing environments can be demanding in this respect. Dust, slurry, curing-room humidity and routine cleaning all place pressure on seals and electrical connections. Abrasive dust around connectors can retain moisture, while a cable trapped under a guard or bent repeatedly can fail internally without obvious external damage.
Cleaning should be controlled. Avoid directing high-pressure water at load cells, connectors or cable entries unless the equipment is specifically designed and protected for that method. Keep connection points clean and dry, and investigate any recurring issue following cleaning or periods of high humidity.
Electrical supply and signal-conditioning faults
Not every drifting force reading originates in the load cell. The indicator, amplifier, analogue-to-digital converter, excitation supply and earthing arrangement all influence the displayed result. An unstable excitation voltage can change the output signal. Electrical noise from motors, pumps, inverters or poor shielding can make a stable measurement appear to fluctuate.
A loose terminal, oxidised connector or damaged screen can cause an intermittent problem that is difficult to reproduce. If the reading shifts when a pump starts, a motor changes speed or nearby equipment is switched on, the investigation should include electrical interference and grounding.
The distinction matters because replacing a load cell will not correct a faulty display unit or cable installation. A competent service inspection should assess the complete measurement chain before parts are changed.
Telling normal variation from a developing fault
The pattern of the error provides useful evidence. A zero change that occurs only during warm-up and then stabilises may indicate thermal settling. Drift that steadily worsens throughout a day, appears after cleaning or changes when a cable is touched suggests an environmental or electrical cause. A persistent calibration error across the range, particularly after an overload or poorly aligned test, raises concern about mechanical damage.
Repeatability is equally revealing. Apply the same known load several times under the same conditions and compare the readings. Then remove the load and allow the equipment to recover before repeating the check. Inconsistent results are often more informative than one out-of-tolerance value.
Do not correct a recurring problem by repeatedly re-zeroing the machine. Zero adjustment may hide the symptom for a short period while leaving a damaged load cell, unstable connection or distorted frame unaddressed. It can also make fault history harder to interpret.
How to reduce load cell drift in service
Good control starts with keeping the load path clean, centred and within the machine’s rated capacity. Test specimens and fixtures should be correctly positioned, bearing surfaces kept in sound condition, and any signs of impact or overload recorded. Operators should avoid using the load cell or platen area as a support point for unrelated work.
Environmental control should be proportionate to the accuracy required. Stable temperatures, sensible warm-up periods and protection from direct heat sources reduce avoidable variation. In damp or dusty areas, inspect cable entries, connectors and protective covers routinely rather than waiting for a reading fault.
Planned servicing should include inspection of mounting hardware, alignment, cable condition and the wider machine structure. It should also include functional checks that distinguish force-control issues from measurement issues. Calibration then verifies performance against a traceable reference and establishes whether the machine remains suitable for its intended testing range.
Calibration intervals depend on use, risk, required accuracy, equipment history and any applicable quality system. A heavily used compression testing machine, equipment exposed to harsh conditions, or a machine that has experienced an overload may need attention sooner than a lightly used unit in a controlled laboratory. An in-date certificate does not remove the need to investigate abnormal behaviour between calibrations.
When drift requires repair or calibration support
Take a drifting machine out of critical use if readings are unstable, if it cannot return reliably to zero, if a known-load check is outside acceptable tolerance, or if overload, impact, cable damage or moisture ingress is suspected. Continuing to test can create a larger problem than the immediate downtime, particularly where results support material acceptance or contractual decisions.
A service engineer can inspect the mechanical installation, test the electrical circuit, assess the indicator and verify the load cell against suitable reference equipment. Depending on the findings, the correct action may be adjustment, cable repair, replacement of a component, machine repair or full calibration. Teur Pro Engineering supports this type of fault-finding with the practical aim of returning testing equipment to accurate, dependable service.
Accurate force measurement is maintained through attention to the whole system, not by treating the load cell as an isolated component. When readings begin to move, recording the conditions, checking the load path and arranging a timely technical assessment will protect both equipment uptime and confidence in every result.