Calibrating a weighbridge means testing the truck scale with standard weights, a substitute load and a loaded test vehicle. The test load goes on the start, middle and end of the deck. In India, a weighbridge used in trade is verified at its site by Legal Metrology and must be re-verified every 12 months, and after any repair or move. On a 40-tonne weighbridge that reads in 10 kg steps, OIML R 76 allows an error of ±15 kg at full load on verification and ±30 kg in service.
What a weighbridge is and how it weighs
A weighbridge, called a dharam kanta in much of India, is a platform built to weigh whole vehicles. Rajasthan's Legal Metrology department lists the static weighbridge (dharam kanta) among the instruments it verifies in situ, where they are installed, alongside fuel pumps and storage tanks.
Modern weighbridges are electronic and carry the deck on strain gauge load cells. A common build for trucks is a 40-tonne, class III weighbridge with a verification interval e of 10 kg, and the examples below use it.
A pit weighbridge sits in a recess, so its deck is level with the road. A surface, or pitless, weighbridge stands on a raised foundation with ramps at each end. Both carry the deck on load cells, and both are tested the same way.
How inspectors test a weighbridge
Indian model approvals are issued under the Seventh Schedule of the Legal Metrology (General) Rules, 2011, and use the accuracy classes of OIML R 76. R 76 sets out these tests for verification:
- Zero and tare. The empty deck must read zero, and the tare function must be accurate.
- Weighing test. Readings are checked at about five loads from the minimum capacity to the maximum.
- Rolling-load test. A load as heavy and concentrated as the usual vehicle, up to 0.8 times the maximum capacity, is placed at the beginning, middle and end of the deck in the driving direction, then in reverse. Each section of a multi-section deck is tested.
- Repeatability. The same load is weighed several times, and the results may not differ by more than the allowed error.
No inspector brings 40 tonnes of weights. R 76 lets a substitute load make up the rest, as long as standard weights cover at least half of the maximum capacity. That share drops to one third if the weighbridge repeats within 0.3e, and to one fifth if it repeats within 0.2e.
The standard weights must have an error below one third of the weighbridge's allowed error. A 1,000 kg weight of OIML R 111 class M1, for example, is allowed ±50 g.
Owners usually share the work. R 76 lets the authority ask the applicant for test loads, equipment and staff. In Jammu and Kashmir, the owner also pays a mobile testing kit charge of ₹2,000 per weighbridge on top of the verification fee.
How much error the law allows
Tolerance is counted in verification intervals, e. A class III weighbridge may be off by ±0.5e up to 500e, ±1e up to 2,000e and ±1.5e up to 10,000e at verification, and by twice those limits in service. The table works this out for the 40-tonne weighbridge above and for a 60-tonne example with a 20 kg interval.
| Weighbridge | Load on the deck | At verification | In service |
|---|---|---|---|
| 40 t, e = 10 kg | Up to 5 t | ±5 kg | ±10 kg |
| 40 t, e = 10 kg | 5 t to 20 t | ±10 kg | ±20 kg |
| 40 t, e = 10 kg | 20 t to 40 t | ±15 kg | ±30 kg |
| 60 t, e = 20 kg | Up to 10 t | ±10 kg | ±20 kg |
| 60 t, e = 20 kg | 10 t to 40 t | ±20 kg | ±40 kg |
| 60 t, e = 20 kg | 40 t to 60 t | ±30 kg | ±60 kg |
In percentage terms, ±15 kg on 40 tonnes is under 0.04 per cent. The minimum capacity matters as well. R 76 defines it as the load below which results may carry an excessive relative error. For a class III weighbridge it is 20e, which is 200 kg when e is 10 kg.
Legal Metrology rules for weighbridges
- Stamped where it stands. A weight or measure that cannot be moved is verified and stamped in situ, and a weighbridge may not be used in a transaction until it is.
- Every 12 months. Weighing instruments are re-verified every 12 months.
- After repair or a move. A repaired weighbridge, or one dismantled and reinstalled elsewhere, must be re-verified before use.
- Apply 30 days early. For instruments that cannot be moved, owners must report to the Legal Metrology officer at least 30 days before the due date.
- Sealed against adjustment. OIML R 76 requires the calibration adjustment of a class III instrument to be sealed, so only a registered repairer may recalibrate a stamped weighbridge.
- Certificate on display. The verification certificate must be displayed where the weighbridge is used.
Missing the date costs money. In Jammu and Kashmir, an application filed after the due date pays a late fee of 50 per cent of the fee for every quarter. A weighbridge that fails gets a rejection certificate; if an authorised repairer fixes it within seven days, it is re-verified for half the fee.
Penalties under the Legal Metrology Act have been eased but not removed. The Jan Vishwas Act, 2023 replaced imprisonment with money penalties in seven sections of the Act from 1 October 2023, the Press Information Bureau notes. The Act still penalises the use of unverified weights and measures.
Static weighbridge or weigh-in-motion?
A static weighbridge weighs a vehicle that has stopped on the deck. A weigh-in-motion (WIM) system weighs it as it drives across, and it follows a separate recommendation, OIML R 134.
R 134 has six accuracy classes for vehicle mass, from 0.2 to 10. The best, class 0.2, allows ±0.10 per cent at initial verification and ±0.20 per cent in service; class 10 allows ±5 per cent and ±10 per cent. WIM systems are tested with reference vehicles whose mass was first found on a static weighing instrument.
A static check is tighter: ±0.10 per cent of 40 tonnes is 40 kg, against ±15 kg for the class III weighbridge above. Accuracy also has a road-safety side. The 2019 amendment to the Motor Vehicles Act raised the overloading fine to ₹20,000 plus ₹2,000 for each extra tonne, as the PIB reported when Parliament passed it.
What throws a weighbridge out between tests
- Foundation movement. A settling foundation or a cracked ramp changes how the deck sits on its load cells.
- Debris and water. Stones, mud or standing water in the pit, or wedged in the gap around the deck, can carry part of the load past the load cells.
- Vehicle position. A truck with an axle off either end of the deck is only partly weighed, however well the weighbridge is calibrated.
- Temperature. Unless its markings state other limits, R 76 expects an instrument to hold its accuracy between −10 °C and +40 °C.
- Cables and junction boxes. Damage or moisture in the wiring between load cells and indicator shows up as drift or unstable readings.
Daily checks a weighbridge operator can do
An operator cannot adjust a stamped weighbridge, but can catch faults early. Check that the empty deck reads zero each morning. Keep the gaps around the deck clear. Weigh the same reference vehicle at regular intervals and log the result, so a drift shows up as a trend. Call a registered repairer, and then Legal Metrology, as soon as a reading looks wrong, because the law requires re-verification after any repair.
Omace scales for loads below a truck
Omace Brands Private Limited has made and supplied weighing scales in India since 1994, from Bagru, Jaipur. For goods weighed before they are loaded, Omace's platform weighing scale range starts at 100 kg. The Omace Om-PS-MS platform kanta weighs 100 kg to 1,000 kg on a mild steel platform of 400 to 900 mm, with a battery backup of about two days, at ₹6,000–₹29,999 including GST (October 2026). The Om-PS series is a Legal Metrology approved model, approved in accuracy class III. Its 1000 kg platform scale reads in 100 g steps on a 750 mm platform for ₹26,999. Omace scales are made in India. As a manufacturer, Omace Brands Private Limited holds ISO 9001:2015, ISO 13485:2016 and EU MDR quality certificates, and CE and US FDA compliance certificates; each is listed with its certificate number on the Omace certificates page. Omace shop, platform, chicken and crane scales leave the Bagru factory verified and stamped by Legal Metrology.
Weighbridges are not part of the Omace catalogue. Omace supplies weighbridges and similar weighing systems on request: call 8690277199.
Every Omace scale is checked before dispatch, and store purchases carry a 2-year warranty on manufacturing defects, excluding batteries and physical damage. More about Omace.
The rules for every trade scale are in what legal for trade means in India. For picking a size, see how to choose an industrial weighing scale. For smaller scales, read how to calibrate a digital weighing scale.
