An industrial weighing indicator looks like a modest instrument - a display, a few keys and a cable to one or more load cells - yet electrically it is a precision measurement system that must keep working on a moving vehicle, in a cold warehouse or on a loading apron where no mains socket exists. In a pallet-truck or forklift onboard scale the load cells are built into the forks or the load carriage, and the indicator computes a legal-for-trade weight while the truck is braking, lifting and travelling over expansion joints. This first paper on nickel-metal hydride power for industrial weighing dissects that load profile from the transducer inward: the constant excitation current the indicator must feed into a strain-gauge Wheatstone bridge, the millivolt-level return signal and the high-resolution sigma-delta conversion that turns it into a weight, the digital filtering that separates a static mass from vehicle vibration, and the periodic bursts from the backlight, thermal printer and wireless module that sit on top of an always-on measurement baseline. It then explains why, when a weight value sets a price or a freight charge, the instrument enters legal metrology under OIML R76 and EN 45501, and why the supply that backs up the weighing function - as distinct from a pump or actuator - carries a metrological, not merely an electrical, responsibility.
Almost every industrial scale measures force with bonded metallic strain gauges arranged in a Wheatstone bridge. Under load the gauges change resistance by a few thousandths, unbalancing the bridge so that, for a typical 5 V or 10 V excitation, the return signal is only some millivolts at full scale. The indicator must therefore generate a stable, low-noise bridge supply (often switchable between 5 V and 10 V) and amplify and digitise the return with a high-resolution sigma-delta analogue-to-digital converter; high-end indicators advertise internal resolution in the millions of displayable divisions while reserving a smaller, metrologically approved number of verified scale intervals for trade use.
Excitation is a continuous load. A 350-ohm bridge draws a fixed current set by the excitation voltage, and indicators are commonly rated to drive several cells in parallel - published instruments accept up to eight analogue load cells of 350 ohm input resistance, which multiplies the excitation current accordingly. The measurement front end, reference and converter run continuously so the scale can track drift, auto-zero and settle quickly; this is the irreducible baseline that any onboard battery must supply for an entire shift.
A bench scale can wait for a perfectly stable reading; a forklift scale cannot. As the hydraulic system lifts the load and the truck travels, the measured force oscillates with mast acceleration, tyre and floor compliance, engine or pump vibration and cornering. The indicator samples far faster than its display rate and applies a chain of averaging, damping and stability detectors, freezing or capturing the weight only when the filtered signal sits inside a defined stability band for a defined time - the basis of onboard 'weigh-as-you-drive' and lifted-load capture.
This digital workload is modest for a modern microcontroller but never zero, and it rises during the capture window when the converter runs at its highest oversampling rate and the processor evaluates the stability criterion in real time. The first animated figure contrasts the indicator's layered current - a flat excitation-and-conversion baseline, a backlight and capture peak, and a short printer or radio burst - while the second shows how a noisy raw force signal is filtered down to a stable, legally valid mass.
Operational weighing is a sequence of functions that all depend on retained data: tare stores the empty-pallet or container weight, accumulation sums successive drafts, and vehicle indicators can hold large libraries - a published vehicle-weighing terminal stores 1,000 groups of tare weights and 1,500 weighing records. Product look-ups, setpoints and calibration coefficients likewise live in memory and must survive a battery swap or a supply interruption without corrupting a legal record.
The power consequence is twofold: a small keep-alive and memory-retention load that must persist even when the main instrument is nominally off, and a clean shutdown that writes the current transaction before the rail collapses. A source whose voltage sags slowly and predictably, rather than dropping off a cliff, gives the indicator time to close the record and raise a low-battery alarm - a characteristic that favours a well-matched, internally fused rechargeable pack over an ageing primary set.
On top of the measurement baseline sit short, higher-current loads. An LED or backlit LCD is the largest steady consumer and is duty-cycled by energy-saving menus; an integrated thermal printer draws a sharp current pulse for each label or ticket; and a radio module - RS-232 to a printer at 600 to 19,200 bit/s in legacy instruments, or a short-range wireless link to a warehouse system - draws a transmit peak well above its receive current. Published wireless forklift scales quote roughly 40 hours of indicator running on an internal 6 V, 4 Ah battery and as long as 120 hours for the wireless link's low-duty regime, illustrating how dominant the display and measurement baseline are relative to brief radio traffic.
Sizing the battery from average current alone is the classic mistake: the converter and excitation baseline sets the energy budget, but the printer or radio transmit peak sets the minimum instantaneous current the pack must deliver without pulling the analogue rail out of its metrological tolerance. Internal resistance and pulse behaviour therefore matter as much as ampere-hours.
The moment a weight sets a price, a tariff, a freight charge or a declared quantity, the instrument is a non-automatic weighing instrument in legal metrology. Internationally the governing recommendation is OIML R76; in Europe it is mirrored by EN 45501 and enforced through the Non-Automatic Weighing Instruments Directive 2014/31/EU, which adds the metrology 'M' mark alongside CE, while in the United States NIST Handbook 44 plays the equivalent role. Load cells carry their own approval, commonly to OIML R60 accuracy class C3, and onboard hardware is frequently sealed to IP68 against wash-down.
These standards treat supply voltage as an influence quantity: the instrument must remain within maximum permissible error across its rated voltage range and warn or behave safely at the low-voltage boundary. An OIML certificate for one hospital-bed scale even states expressly that its optional battery is 'not for any weighing function but the bed actuators only' - a precise illustration that a battery which merely moves a motor is metrologically irrelevant, whereas the source feeding the weighing chain is part of the approved instrument and cannot be substituted casually.
Pulling the analysis together, an onboard weighing indicator needs a source that supplies a continuous bridge-excitation and conversion baseline for a full shift, delivers printer and radio peaks without rail disturbance, retains tare, calibration and transaction memory through supply breaks, behaves predictably at the low-voltage metrological boundary, and survives vehicle vibration and cold-store temperatures under an IP-rated enclosure. The second paper turns this regime into a concrete pack and charging design and compares sealed nickel-metal hydride honestly against sealed lead-acid and lithium; the third maps the type-approval, EMC, environmental and battery-standard evidence a weighing-instrument manufacturer must assemble.
Treating the battery as part of the measurement chain - rather than a generic accessory - is the mindset that separates an onboard scale that weighs accurately and keeps its records through every shift from one whose readings drift, reset or fail precisely when a trade transaction depends on them.
Weijiang Power designs and manufactures sealed nickel-metal hydride cells and matched industrial packs for remote, off-grid and safety-related equipment, and supports OEM partners with IEC 61951-2 performance files, IEC 62133-2 safety evidence, pulse-load characterisation, wide-temperature testing and charger/pack co-validation. Tell us your duty cycle, peak current, temperature envelope, autonomy target and the standards your product must meet, and our engineers will specify a cell-and-pack combination that protects runtime, reliability and service life. Review the range on the products page.
