Checkweighers for packaging lines · OIML R 51 category X accuracy classes and class factor, maximum mean error and standard deviation by pack weight, EU average-quantity rules and the EEC sign
A checkweigher weighs every pack moving along a production line and sorts out those outside set weight limits. Ask three things first: whether it is used to show legal compliance of prepacked quantities, since that calls for a verified instrument in the right accuracy class; how heavy the packs are and how fast they pass, since accuracy depends on both; and how rejects are removed and recorded.
Automatic checkweighers that weigh prepacks in motion and sort them by weight, stand-alone or combined with metal detectors or labellers. Static scales, load cells, multihead weighers that dose product, and metal detectors alone are outside this page except where compared.
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01
OIML R 51-1 defines a checkweigher as an automatic catchweigher that sorts prepackages of different mass into sub-groups by their difference from a nominal set point. Category X applies only to checkweighers used to check prepacked products under OIML R 87, divided into accuracy classes XI, XII, XIII and XIIII, each supplemented by a maker-declared factor (x) of 1, 2 or 5 × 10ᵏ; category Y covers weigh-price labellers, postal scales and other catchweighers. For category X the maximum permissible mean error is ±0.5 e at initial verification (±1 e in service) for the smallest loads in each class, rising to ±1 e (±2 e) and ±1.5 e (±3 e) for larger loads, where e is the verification scale interval. [1]
The maximum permissible standard deviation, for (x) = 1, is 0.48% for packs up to 50 g, 0.24 g for 50–100 g, 0.24% for 100–200 g, 0.48 g for 200–300 g, 0.16% for 300–500 g, 0.8 g for 500–1,000 g, 0.08% for 1–10 kg and 8 g for 10–15 kg at initial verification, with in-service values about a quarter higher; the limits are multiplied by (x), which must be below 1 for classes XI and XII, not above 1 for XIII and above 1 for XIIII. The type approval certificate states the class, and the instrument must show Max, Min, e and its class X(x) or Y(y). [1]
Editorial calculation: for a 400 g pack at (x) = 1 the permitted standard deviation is 0.16% × 400 g = 0.64 g at initial verification and 0.2% = 0.8 g in service; a checkweigher declared at (x) = 0.5 must halve those to 0.32 g and 0.4 g. [1]
For heavy cases, bags and totes, Thermo Fisher's Versa Frame 44 shows what a machine data sheet adds to the class: packages up to 45 kg (100 lb) and 1,143 mm long, line rates up to 100 packages per minute, belt speeds of 10 to 122 m/min (33 to 400 fpm), belt widths of 457, 610, 762 or 914 mm, four strain-gauge load cells, and accuracy of ±15 to 25 g below 100 fpm or ±25 to 45 g above 150 fpm for 40 lb packages. [3]
Editorial calculation: 40 lb is about 18.1 kg, so ±15 to 25 g is about ±0.08% to ±0.14% of the package mass at the lower speed; the maker states accuracy as a ± band that worsens with speed, whereas OIML R 51 limits the mean error and standard deviation, so ask for the test data in the form your verification uses. [3] [1]
Give the supplier the pack types with nominal weights, weight range and dimensions, line speed in packs per minute, required accuracy class X(x) and verification, reject zones and reject method (air blast, pusher, flap), reject confirmation and bin locking, data export and statistics, combination with metal detection or labelling, washdown and IP rating, frame material, power supply, conveyor width and height, and quantity.
02
EU Council Directive 76/211/EEC covers prepackages of constant nominal quantity from 5 g or 5 ml to 10 kg or 10 l. Packers must ensure that the actual contents are not less, on average, than the nominal quantity; that the proportion of packs with a negative error greater than the tolerable negative error is small enough to pass the reference tests; and that no pack with a negative error greater than twice the tolerable negative error bears the EEC sign. The tolerable negative error is fixed by a table in classes by nominal quantity, rounded up to the nearest 0.1 g or 0.1 ml, and batches are checked by single or double sampling plans, with packs below the minimum acceptable contents counted as defective. [2]
Editorial note: a checkweigher set to reject packs below the minimum acceptable contents and to monitor the running average supports these rules; ask the supplier which statistics, alarms and records the controller provides and whether the instrument is verified for this legal use in your market.
Anritsu's page for its SSV checkweighers shows the cost side of the same rules: it states 3-sigma accuracy with a 0.03% error margin, a system length as small as 545 mm (21.5 in), and a worked example in which a line making 120 boxes per minute with 5 g giveaway per box worth $0.05 loses more than $86,000 a month, and cutting giveaway to 3 g ($0.03) saves up to $34,500 a month. It describes two calibrations: static calibration (sensitivity correction) with a master weight or master product and no products moving, and dynamic calibration in which the master product is passed back and forth 10 times while in motion. [4]
Editorial calculation: Anritsu's monthly figures fit about 8 hours a day for 30 days: 120 × 60 × 8 × 30 = 1,728,000 boxes, × $0.05 ≈ $86,400, and × $0.02 saved ≈ $34,560. A maker's 3σ error margin is not the OIML R 51 maximum permissible standard deviation (0.16% at 300–500 g for (x) = 1), so ask for the class X(x) certificate and test data at your pack weight and belt speed. [4] [1]
03
Suppliers linked to this page list checkweighers; each card links to the page reviewed.
Listings include automatic and dynamic checkweighers, checkweighers combined with metal detectors or labelling, multi-lane small-pack checkweighers and checkweighers integrated with filling and capping lines; ask each for the accuracy class and certificate, standard deviation at your pack weight and speed, reject system and data output.
04
This is a functional reference built from the sources cited; it is not one maker's specification.
| Element | Role | Fix in the order |
|---|---|---|
| Infeed conveyor | Spaces packs for weighing. | Belt and spacing. |
| Weigh conveyor and load cell | Weighs in motion; four strain-gauge cells on one heavy-duty frame. [1] [3] | Max, Min, e. |
| Controller and display | Shows result and markings; data via Ethernet, serial, USB, Modbus; runs static and dynamic calibration. [1] [3] [4] | Statistics, data. |
| Reject device | Sorts packs into sub-groups; air pusher or swing gate. [1] [3] | Method, bins. |
| Frame and guarding | Support; stainless frame, washdown options. [3] | Material, IP. |
05
A checkweigher quotation needs values for your packs. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Weighing range (g) | Pack range 5 g–10 kg under 76/211; heavy-duty example up to 45 kg. [2] [3] | Min and Max. |
| Accuracy (g) | Std dev e.g. 0.16% at 300–500 g, (x)=1. [1] | Class X(x) and test data. |
| Throughput (pcs/min) | E.g. up to 100 packages/min on a heavy-duty unit. [3] | Rate at your pack. |
| Air supply (bar) | E.g. 5.5–6.9 bar for air-pusher reject. [3] | Pressure; consumption. |
| Belt speed (m/min) | E.g. 10–122 m/min. [3] | Speed. |
| Conveyor width (mm) | E.g. 457, 610, 762 or 914 mm. [3] | Width. |
| Power supply (V AC) | E.g. 110–130 or 200–250 V AC ±10%, 50/60 Hz single phase; 300 VA control. [3] | Supply. |
| Operating temperature (°C) | E.g. 5–40 °C, 20–90% RH non-condensing. [3] | Range. |
| Ingress protection | E.g. IP65 stainless load cell option; IP66 option pack. [3] | IP for washdown. |
| Frame material | E.g. stainless steel frame. [3] | Stainless grade. |
| Machine weight (kg) | Not stated in reviewed sources. | Weight. |
06
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Packs: [nominal weights; dimensions; range] Speed: [packs per minute] Accuracy: [class X(x); verification] Rejects: [zones; method; confirmation] Data: [statistics; export; alarms] Combination: [metal detector; labeller] Site: [washdown; IP; power; conveyor height]
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OIML R 51 puts checkweighers for prepacks in category X, classes XI to XIIII, with a maker-declared factor (x) that scales the permitted standard deviation. [1]
At (x) = 1, OIML R 51 permits a standard deviation of 0.16% for 300–500 g packs at initial verification, or 0.8 g for 500–1,000 g. [1]
Directive 76/211 requires packs to average at least the nominal quantity, few to exceed the tolerable negative error, and none bearing the EEC sign to exceed twice it. [2]
Thermo Fisher lists up to 100 packages per minute at 10–122 m/min for its Versa Frame 44, with accuracy widening from ±15–25 g to ±25–45 g at higher speed on 40 lb packages. [3]
Anritsu describes static calibration with a master weight or product at rest, and dynamic calibration that passes the master product back and forth 10 times in motion. [4]
Sources checked 2026-10-12. OIML R 51 is the international recommendation for automatic catchweighing instruments; Directive 76/211/EEC is EU law on prepack quantities; Thermo Fisher's and Anritsu's product pages give their own checkweighers' data. National rules decide which apply to your line.
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