TECH NOTE 06 / Mechanical protection
Miniature load cell overload stops: limits, gaps and impact energy
A protection percentage is not an extension of the calibrated measurement range.
A protection percentage is not an extension of the calibrated measurement range.
Stops need a defined load path, clearance/tolerance window and direction-specific rating.
Impact energy and stopping distance cannot be approved from a static overload percentage alone.
01 / ENGINEERING DECISION
Separate measurement range, overload and failure limits.
An overload protected miniature load cell can include a mechanical contact path that limits flexure motion or carries some additional load after engagement. Its useful measuring range remains the stated calibrated range. Contact with a stop can change the response and invalidate force interpretation even if the element survives.
“1000% protection” must be attached to an exact part, direction and load condition. It is not a general permission to apply ten times rated force repeatedly, to strike the fixture or to use a similar-looking sensor at the same percentage.
| Term / event | Question to resolve |
|---|---|
| Calibrated range | Where are measurement errors specified? |
| Specified safe overload | What load condition preserves the stated acceptance criteria? |
| Ultimate / destructive limit | What structural failure boundary is described? |
| Stop contact | When does the additional mechanical load path engage? |
Supporting scope: FUTEK LSB200 drawing FI1455-B ↗ · HBK force glossary ↗
02 / ENGINEERING DECISION
Read the current item scope and the historical exceptions.
The current cited LSB200 FI1455-B sheet covers the low-capacity 10–250 g family and prints a 1000% safe-overload figure. An older item sheet covers a broader range and prints a 200% tension-only exception for 50–100 lb. These documents must not be collapsed into an unconditional family-wide statement.
A historical 10 N paired-system item sheet is another configuration, not evidence that the current low-range drawing covers 10 N. Treat the original documents as separate dated/item-specific evidence. None of these original-brand ratings establishes an MT-ILC-SUB protection rating.
| Original document | Relevant distinction | Use in a selection review |
|---|---|---|
| Current LSB200 FI1455-B | Low-capacity 10–250 g scope; 1000% printed | Read exact item, direction and conditions. |
| Older FSH00107 item sheet | Broader historical scope; 50–100 lb tension exception | Do not apply its blanket feature headline to every row. |
| Historical QSH01737 paired item | A particular 10 N sensor/USB association | Do not merge with the current low-range sheet. |
| Proposed MT-ILC-SUB | Own drawing and test record required | No original percentage is transferred. |
Supporting scope: FUTEK LSB200 drawing FI1455-B ↗ · FUTEK historical FSH00107 item sheet ↗ · FUTEK historical QSH01737 paired item ↗
03 / ENGINEERING DECISION
A stop adds a load path after a defined displacement.
Before contact, the sensing element carries force through its compliant measurement path. After the stop engages, load can be shared with a second, stiffer path. The exact partition depends on the element, stop and surrounding stiffness; it is not correct to assume the sensing element becomes completely unloaded.
The illustration shows a conceptual bypass, not an internal drawing of a vendor sensor and not a machining plan. Tension and compression may require different contact surfaces and gaps. Thread-root loads, lateral forces and cable forces need separate consideration.
Supporting scope: FUTEK LSB200 drawing FI1455-B ↗
04 / ENGINEERING DECISION
The clearance window needs both operating and damage bounds.
For a simple displacement-based screen, the smallest possible gap should exceed the largest intended operating displacement, while the largest possible gap should remain below the displacement at which unacceptable damage would begin. Those two inequalities are only useful when both bounds are known for the actual design.
Tolerance stack, temperature, preload, wear and assembly changes can move the contact point. There is no generic micrometre gap setting that safely converts an unprotected sensor into a protected one. Obtain manufacturer evidence instead of filing, bending or adjusting a sensing flexure.
Required screening window: operating displacement_max < gap_min, and gap_max < unacceptable-damage displacement_min
| Input | Include in the evaluation |
|---|---|
| Operating motion | Maximum local elastic motion and preload. |
| Gap tolerance | All contact/assembly dimensions and thermal changes. |
| Contact capacity | Stop, fasteners and supporting structure. |
| Direction | Separate tension/compression behavior. |
| Acceptance after overload | Zero return, span and any required recalibration. |
Supporting scope: FUTEK LSB200 drawing FI1455-B ↗ · HBK force glossary ↗
05 / ENGINEERING DECISION
Worked example A: a percentage still needs conditions.
For a hypothetical 1 N rated sensor, 1000% of that rating is 10 N. This arithmetic does not establish that a particular sensor can withstand that load, in which direction, for how long or with what post-event error. It certainly does not extend a 1 N calibrated span to 10 N.
If a system needs to measure 8 N during operation, an assumed 1 N sensor with an overload headline is not an 8 N measurement solution. Choose an appropriate calibrated range and then evaluate protection for assembly/transient loads.
| Question | Consequence |
|---|---|
| 1 N × 1000% | 10 N arithmetic only. |
| Measure an 8 N operating force | Need an appropriate calibrated measurement range. |
| Survive an unexpected event | Need exact directional overload and acceptance evidence. |
06 / ENGINEERING DECISION
Worked example B: stopping distance changes the force scale.
Assume a 0.05 kg moving object reaches 0.20 m/s. Its kinetic energy is 0.001 J. Dissipating that energy over 0.10 mm corresponds to a 10 N energy-equivalent average resisting force; over 0.01 mm it corresponds to 100 N. Gravity, preload and other energy sources are excluded from this simple calculation.
These are not peak forces, measured stop reactions or predicted loads in the sensor flexure. Peak force can exceed the average and depends on compliance/damping and contact dynamics. A static overload percentage cannot validate this impact case.
Kinetic energy E = mass × speed² / 2; energy-equivalent average resisting force = E / stopping distance
| Energy to dissipate | Assumed distance | Equivalent average resisting force |
|---|---|---|
| 0.001 J | 0.10 mm = 0.00010 m | 10 N |
| 0.001 J | 0.01 mm = 0.00001 m | 100 N |
| Actual mechanism | Needs a dynamic model/test | Peak and load partition remain unknown. |
07 / ENGINEERING DECISION
Treat an overload event as a reason to check the measurement.
Plan handling, assembly and motion limits so the sensor is not the only means of arresting a moving mechanism. Use appropriate fixtures and system protection, and verify the proposed load path before intentional motion. A display or controller limit cannot prevent every assembly or unpowered impact.
After a suspected event, retain the circumstances and check zero return and the agreed reference response before relying on the result. A zero that looks normal is not evidence that span, hysteresis or insulation remains unchanged. Follow the actual manufacturer’s inspection and recalibration process.
- Record direction, estimated load/energy, fixture state and any stop contact.
- Inspect the approved mechanical and cable features without altering the flexure.
- Compare zero and known-force responses under the agreed procedure.
- Quarantine or return a suspect unit according to the manufacturer’s acceptance rules.
Supporting scope: HBK force glossary ↗
08 / ENGINEERING DECISION
Request directional protection evidence with the sensor.
Include working range, assembly force, transient duration, moving mass/speed where relevant, attachment geometry and available protective travel. Ask for the design’s tension/compression overload scope, gap/stop drawing where available and post-event acceptance criteria.
For a subminiature sensor request, protection and useful resolution must be reviewed together. The presence of an S-shaped body or visible slot alone does not prove a particular overload-stop mechanism or rating.
Resolve the fit, signal and calibration questions.
Can a 1 N sensor with 1000% protection measure 10 N accurately?
Not on that basis. Protection concerns the stated overload condition; measurement errors apply within the calibrated range. Request an appropriate range for the operating force.
Does a stop protect both tension and compression?
Only if the exact design and rating say so. Different directions may have different contact surfaces, clearances and limits.
Can a static overload figure approve a dropped mass?
No. Impact depends on energy, stopping distance, compliance, damping and load partition. Obtain a relevant dynamic assessment or test.
Can I adjust a stop using a generic gap value?
No. A valid window needs the actual operating and damage displacement bounds plus tolerances. Do not modify the flexure or stop without the manufacturer’s approved procedure.
Does a normal zero prove the sensor survived unchanged?
No. Span, hysteresis, insulation or other properties can still be affected. Apply the agreed inspection and reference checks.
Do the original LSB200 percentages apply to MT-ILC-SUB?
No. Original item sheets establish only their own scope. Request the proposed MT-ILC configuration’s drawing, directional rating and acceptance evidence.
ENGINEERING RFQ / SAMPLE REQUEST
Send the load case.
Define the interfaces.
Include both thread ends, working and peak force, available space and the signal your controller expects.
Company and university email domains are preferred. Prototype and research inquiries are welcome.
inquiry@inlineloadcell.com ↗