If you are weighing how to choose a load moment indicator (LMI) for a crane, excavator or wheel loader, this guide walks the decision the way our field engineers do — machine first, catalog second. The regulation requires one, the insurance policy mentions one, and the supplier’s quotation lists three different models at three different prices. What buyers discover too late is that an LMI is not an accessory you pick from a catalog page. It is a measuring system engineered around a specific machine — buy the wrong one and you get a display that lights up, alarms that fire at the wrong moments, and an operator who learns to ignore both.
This guide is the checklist we use internally when matching a system to a customer’s machine — truck cranes, crawler cranes, excavators, loaders and the less common frames in between. It covers what to answer before comparing prices, how to read a spec sheet, and the calibration step that decides whether the system gets used or quietly switched off.
What a load moment indicator actually does
An LMI does not weigh the load directly. It measures the geometry and the hydraulic effort of each lift — boom angle, boom length, cylinder pressure — calculates the moment in real time, and compares it against the rated capacity chart stored in the controller. Approaching the limit, it warns the operator. Crossing it, it cuts the dangerous movements through a relay.
If you are deciding between an indicator and a cutoff-only device, start with the difference between an LMI and a load limiter — the rest of this guide assumes you want the full monitoring chain. Our crane-by-crane LMI hub keeps the complete machine list in one place.
Step 1 — Start with your machine, not with the catalog
The most common buying mistake is choosing by one number: rated capacity. Two 25-ton cranes can need completely different sensing chains. What the system must watch is decided by the machine’s structure, not by its badge.
| Machine | What the system must monitor | Typical range | Reference system |
|---|---|---|---|
| Truck crane / rough-terrain crane | Boom length, luffing angle, hoof pressure | 10–100 t | SZ-M100 mobile crane LMI |
| Grúa sobre orugas | Same chain, larger range, crawler-specific charts | up to 260 t | Grúa sobre orugas LMI |
| Spider / mini crawler crane | Outrigger posture + multi-configuration moment | 0.8–20 t | SZ-SC01 spider crane LMI |
| Marine & ship crane | Moment under pitch and roll, marine sealing | varies | Ship crane LMI |
| Excavator | Boom / arm / bucket cylinder pressures | 10–100 t | Indicador de carga de la excavadora |
| Wheel loader | Lift cylinder pressure + trigger position on the arm | 1–20 t | third-generation wheel loader scale |
| Forklift / telehandler | Mast load, stability moment at height | 2–25 t | Telehandler LMI |
| Reachstacker | Boom moment at eccentric load centers | 10–45 t | Reachstacker load indicator |
| Side boom pipelayer | Boom moment with offset CG loads | up to 90 t | Side boom load indicator |
| Material handler | Continuous-duty moment under cycling loads | 10–50 t | Material handler load indicator |
| Articulated boom crane | Knuckle angle compensation | 3–50 t | Articulated boom LMI |
A spider crane working indoors illustrates why this matters. Its rated capacity changes with every outrigger extension, so the LMI must sense support posture, not just boom geometry — a truck-crane unit without outrigger inputs cannot protect this machine no matter what the box claims.
If you run a mixed fleet, resist the temptation to buy one model for everything. A wider range with configurable capacity charts is cheaper than three mismatched systems — but only if the sensing chain still matches each frame. Ask the supplier to quote per machine type and to show the sensing diagram for every unit, not just the first one.
Step 2 — Follow the sensing chain, Every load moment indicator is only as good as its weakest sensor, so walk the chain in order.
Every LMI is only as good as its three sensing points. This is where low-cost systems cut corners, and where failures start.
El sensor de ángulo sits on the boom pivot and reports luffing angle; a dual-axis unit also catches side tilt, which matters on crawler and spider frames. The hydraulic pressure sensors (0–40 MPa, 4–20 mA, 0.5% FS) convert cylinder pressure into load — accuracy here is the ceiling for the whole system’s accuracy. A length or trigger sensor closes the chain on telescopic booms and loader arms.
Three environment numbers separate an industrial sensor from a showroom one: IP65 sealing against dust and washdown, a −20 °C to +70 °C window for winter pipeline work and summer decks, and EMC-hardened cabling that survives engine-bay interference. Ask for these three numbers before anything else.
Step 3 — Read the spec sheet like an engineer
Spec sheets list the same line items in a different order. Here is a real one — our SZ-M100 mobile crane system — with the questions each line should trigger.
| Spec line | Valor | What to check against your machine |
|---|---|---|
| Gama | 5–260 t | Cover your max capacity y the smallest lift you still want displayed — one range rarely fits a mixed fleet |
| System error | ±3% | At 100 t that is ±3 t. Is that acceptable for your lift plans and site rules? |
| Display error | ±5% | What the operator sees vs what the controller computed — matters for trainees |
| Protección | IP65 | Enough for washdown and dust; port and marine work should ask for higher |
| Temperatura | −20…+70 °C | Winter pipeline and desert quarry both sit inside; verify your extremes |
| Supply voltage | DC 9–36 V | Wide-input design tolerates cold-crank dips and 24 V truck electrics |
| Relay output | AC220 V / 3 A | Confirm it can actually cut your crane’s motion circuit — ask for the wiring diagram |
Step 4 — Compliance and documentation
Regulators treat overload protection as mandatory equipment, not an option. ISO 10245 series for cranes, EN 13000 for mobile cranes and China’s GB/T 12602 all describe what a load limiting device must detect and do. If your cranes cross borders — rental fleets, port contracts, EPC projects — the paperwork travels with the machine: a calibration certificate, the rated capacity chart used by the controller, and manuals in the operator’s language. Ask the supplier for all three at quotation stage, not after delivery.
Step 5 — Installation and calibration decide whether it gets used
A correctly specified system can still fail in the field for one reason: nobody calibrated it. Installation places the sensors; calibration teaches the controller what “zero” and “known load” look like on your machine.
Sensor layout on an excavator: indicator, arm sensor, boom sensor, pressure sensor and vehicle body sensor positions
Plan for a working day of sensor fitting and cabling, then a half day of calibration with known test weights across at least three points of the capacity chart. After a wire rope change, boom repair or seasonal temperature swing, re-check zero — an uncalibrated display trains operators to distrust the system, and that is how LMIs end up switched off.
Calibration discipline is also what made our Mongolia fleet rollout measurable: the customer’s XCMG wheel loader ran a 20-day field trial on our third-generation weighing system before committing to fleet-wide installation.
What it costs — A properly specified load moment indicator costs a fraction of a single overload accident and what skipping it costs
We quote per machine rather than publishing a price list, because the sensing chain differs by frame. A better question for your budget: what does one incident cost? A tipped crane means a written-off machine, a stopped site, an investigation, and in the worst case injuries — costs that no LMI quotation will ever approach. Frame the purchase as insurance with a display, not as an accessory.
Frequently asked questions
What is the difference between a load moment indicator and a load limiter?
An LMI continuously displays the measured moment against the rated capacity chart; a load limiter (SLI) focuses on intercepting dangerous movements at a set threshold. Most modern SeeZol controllers combine both.
How accurate is a crane load moment indicator?
Typical figures are ±3% system error and ±5% display error of full scale — on a 100 t lift, ±3 t of system tolerance. Calibration quality with known test loads matters more than the datasheet number.
Can one load moment indicator fit different crane models?
No. The sensing chain, capacity chart and alarm logic are engineered per machine family — a spider crane needs outrigger posture sensing; an excavator reads cylinder pressures instead of boom length.
Does an LMI work in extreme temperatures?
Industrial systems are rated −20 °C to +70 °C with IP65 sealing — winter pipeline work and summer decks are covered. Below −20 °C, request a low-temperature display option.
How long does installation and calibration take?
About one working day for sensors and cabling, plus half a day of calibration with known test weights. Uncalibrated installs are the main reason operators stop trusting the display.
How often should a load moment indicator be recalibrated?
Re-check after any wire rope change, boom repair, structural modification or long-distance transport, and verify zero at least once a season. Fleets on multi-shift duty add a mid-year check.
Is a load moment indicator the same as an on-board weighing system?
No. An LMI is a safety device — its job is comparing moment against the rated chart and cutting dangerous movements. A weighing system is a production tool — its job is measuring bucket and payload weights for trade and logistics. The sensing chains overlap, but accuracy targets, alarms and data outputs differ.
Can the system record data for fleet management?
Yes. Current controllers store local history, and third-generation platforms such as the SZ-LD100P upload load data to a cloud dashboard for multi-site oversight.
Five buying mistakes we see most
After years of retrofitting fleets, the same five mistakes keep showing up in failed installations. None of them are about price.
- Buying by tonnage alone. A 25 t rough-terrain crane and a 25 t truck crane share a badge, not a sensing chain. Match the structure first.
- Treating calibration as optional. The system arrives “pre-configured” and goes to work uncalibrated. Within a month the operator ignores it.
- Skipping the environment numbers. A display rated for an office fails its first winter; pressure sensors without proper sealing drift after the first washdown.
- Accepting a generic capacity chart. The controller must run the chart that matches your boom configuration and serial range, not “a similar model”. Ask which chart version ships with the unit.
- Forgetting the spare-parts chain. Sensors fail before controllers do. Before signing, ask the lead time and price for a replacement angle sensor and pressure sensor — if the answer is “we will check”, keep looking.
How to Choose a Load Moment Indicator: The 5-Point Checklist
- Machine first: match the sensing chain to your frame, not the tonnage badge.
- Sensors: confirm IP65, −20…+70 °C, EMC cabling — in writing.
- Spec sheet: ±3% system error understood against your real lift plans.
- Cumplimiento: ISO 10245 / EN 13000 / GB/T 12602 documents promised at quotation.
- Calibración: scheduled with test weights, and re-checked after rope or boom work.
Answer these five and the quotation comparison becomes straightforward. If you want a second opinion on your machine list, send our engineering team your crane models, capacities and working environment — we will return a configuration proposal within one business day.
