Developing Scale and Metering Device Calibration and Verification Procedures

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Regulatory Authority – Feeds RegulationsFootnote 1

Every feed shall have the uniformity of mix, the chemical composition and the physical composition necessary for it to be efficacious for the purpose for which it is manufactured, sold or represented.

General Principles

  • All scales and metering devices used in the making of feed should be appropriate for the range of weights or volumes to be measured.
  • All scales and metering devices used in the making of feed should be calibrated and maintained properly to avoid errors in measurement of medications and other ingredients.
  • All scales and metering devices used in the making of feed should be tested for accuracy.

The following principles should be considered when designing scale and metering device verification procedures used in a particular facility:

1. The scale and metering device calibration and verification procedure should be defined

This written procedure should specify:

  • the specific scale or metering device
  • the capacity of the scale or metering device
  • the graduation of the scale or metering device
  • the accuracy of the scale or metering device
  • a description of what records/documentation will be maintained
  • the method and frequency of calibrationFootnote 2 of all scales and metering devices
  • the method and frequency of testing the scales and metering devices for accuracy - to include acceptable tolerances
  • the corrective actions to be taken when measuring devices are determined to be out of tolerance

The following information should be used as a starting point to establish on-site guidelines for the operation of scale and metering devices.

Equipment

Manufacturing equipment - Scales and metering devices should be suitable for their intended purpose in terms of capacity, graduation, and accuracy.

The suitability of the scales/metering devices can be determined by comparing the feed formulae in use, specifically the batch size and theoretical inclusion levels to the capacity, graduation and accuracy of the scales and metering devices.

Capacity

Scales: the greatest weight that can be weighed on a given scale.
Metering devices: the maximum quantity of an ingredient that can be delivered to the mill per unit of time.

Feed formulae must not exceed the capacity of the scale or metering device.

Graduation

Scales: the finest division on a scale beam, digital readout, printer.
Metering devices: the incremental dial settings that control product flow to the mill.

Medicated ingredient inclusion levels must reflect the graduation of the scale or metering device

Accuracy

Scales: tolerance or variance from true weight. Should be 0.2% of the capacity of the scale or ± 1 graduation, whichever is greater.
Metering devices: tolerance or variance from target output. Should be 5% of target output, or ± 1 graduation, whichever is greater.

2. Schedule of tests

Factors to be considered when determining the frequency of scale and metering device testing include:

  1. age of scale or metering device
  2. type of equipment
  3. tonnage of feed manufactured
  4. source of medication (medication with a Drug Identification Number (DIN) vs. less concentrated)
  5. types and amounts of feed ingredients being weighed or metered by specific scales or metering devices

Generally, verifying the accuracy of the scales and metering devices within 90 days of the installation of new or replacement equipment and a minimum of once every year thereafter would be considered acceptable.

3. Calibration procedures

The calibration of scales and metering devices used in the making of feed is designed to ensure that their accuracy is maintained in accordance with the applicable in-service limits of error for those scales and metering devices set out in Divisions VI and XI of Part V of the Weights and Measures Regulations.

4. VerificationFootnote 3 Testing procedures

Testing equipment: Certified weights, second scale, flow meters, timers, revolution counter

Identification of Scale/Metering Device:

These written procedures apply to the following scale/metering device:

Name:
Model:
Serial #:

For Scales:

Using certified test weights, add 5 known weights to the scale (trying to approach scale maximum or at least working level). Record weight after each addition on the scale accuracy verification record. Remove the weights in reverse sequence. Record the weight as each weight is removed and when all weights have been removed on the scale accuracy verification record.

Load scale to appropriate working level. Record weight. Using certified test weights, add 5 known weights to the scale (trying to approach scale maximum or at least working level). Record weight after each addition on the scale accuracy verification record. Remove the weights in reverse sequence. Record the weight as each weight is removed and when all weights have been removed on the scale accuracy verification record.

Load scale to maximum capacity. Remove weight to ensure scale returns to zero.

For Metering Devices:

For a minimum of two batches, check the calibration of the metering device against the theoretical formula using the following procedures.

Run the metering device for each ingredient for a fixed period of time. Weigh each individual ingredient using a scale that has been verified for accuracy. Compare the actual weights to the theoretical weights. Record actual and theoretical weights on the metering device accuracy verification record.

Prescribed Critical Limits

Scales and metering devices are considered to be capable of producing feeds with the correct chemical composition when scales and metering devices are suitable for the range of weights or volumes to be measured, and testing confirms the following.

Accuracy:

Scales: The scale will be deemed to be accurate if the variation from the true weight is less than 0.1% of the capacity of the scale or " one graduation, whichever is greater, at the time of installation for new scales. Scales which have been in operation should have a maintenance tolerance of 0.2%. For example, a 10 kg capacity micro scale (with .01 kg graduations) that has been in operation should not vary more than (10 kg × 0.2% = 0.02 kg) 0.02 kg from a test weight.

Metering devices: The metering device will be deemed to be accurate if the variation from the true weight is within 5% of the target output or deviation does not exceed the amount delivered by one increment change in the meter setting. For example, a proportioner mixer intended to mix a medicated macro premix at 2.5% of the mix should be within a range of (2.5% × 5% = 0.125%) 2.375 - 2.625% of the total mix.

Corrective Actions

Should the initial scale/metering device test be outside the critical limits, the manufacturer:

  • should evaluate the use of the scale/metering device until its accuracy is within critical limits (a scale service company may have to be called to service the scale/metering device).
  • should evaluate the sale and use of all lots of animal food that are likely to be affected by the discrepancy

After the repairs/modifications have been made, a second test for accuracy should be performed.

Documentation and Records

The following documents and records are required:

  • Documentation to support the suitability of the equipment for the intended purpose (e.g., equipment specifications).
  • Records of calibration
  • Records of verification of accuracy of measuring devices. For example, test weights of certified weights, test weights of actual product as measured on a second scale, etc.
  • Records of maintenance and repair
  • Records of corrective actions when measuring devices are determined to be out of tolerance

Appendices

  • Appendix I Sample Checklist for Scales and Metering Devices
  • Appendix II Sample verification/calibration records

Appendix I - Checklists for Scales and Metering Devices

The suitability of the scales/metering devices can be determined by comparing the feed formulae in use, specifically the batch size and theoretical inclusion levels to the capacity, graduation and accuracy of the scales and metering devices. The following tables may be used to perform these comparisons.

Checklist for Scales Used in the Manufacture of Feeds

1. Identification of the Scale (e.g., name, location, model, serial number, etc.)

2. Ingredients Weighed by the Scale

  • checkbox Grains
  • checkbox Protein Ingredients/Protein Supplements
  • checkbox Macro Premixes
  • checkbox Micro Premixes
  • checkbox Mineral Ingredients/Vitamins
  • checkbox Medicating Premixes (DIN Products)

3. Date of Scale Installation:

4. Suitability of Capacity of the Scale (Maximum weight measured must not exceed capacity)

Capacity of scale (from Operator Manual):

Maximum weight measured by scale:

5. Suitability of Accuracy of the Scale (Minimum weight measured must not be less than the sensitivity)

Sensitivity of scale (the smallest weight that will cause the scale indicator to move as determined annually by testing):

Minimum weight measured by scale:

6. Suitability of Graduation of the Scale (Weights measured must be in full graduations)

Graduation of scale (the finest division on a scale beam, digital readout, printer):

Most precise weight measured by scale:

Checklist for Metering Devices Used in the Manufacture of Feeds

1. Identification of the Metering Device (e.g., name, location, model, serial number, etc.)

2. Ingredients Weighed by the Metering Device

  • checkbox Grains
  • checkbox Protein Ingredients/Protein Supplements
  • checkbox Macro Premixes
  • checkbox Micro Premixes
  • checkbox Mineral Ingredients/Vitamins
  • checkbox Medicating Premixes (DIN Products)

3. Date of Metering Device Installation:

4. Suitability of Capacity of the Metering Device (Maximum weight measured must not exceed capacity)

Capacity of metering device (from Operator Manual):

Maximum weight measured by metering device:

5. Suitability of Sensitivity of the Metering Device (Minimum weight delivered by the metering device must not be less than the amount delivered with a single increment change in dial setting)

Sensitivity of metering device (the smallest weight that is delivered by a single increments change in the dial setting as determined annually by testing):

Minimum weight metered by device:

6. Suitability of Graduation of the Metering Device (Amounts metered must be in full graduations)

Graduation of metering device (the finest division on the dial, digital readout, etc.)

Most precise weight metered by device:

Appendix II - Sample verification/calibration records

Following are two examples for documentation of scale calibration/verification, one from a commercial scale company and the other from a feed manufacturer's in-house quality assurance program.

Feed Scale Co.

Date of Service: space

Make: space

Model: space

Serial Number: space

Location: space

Capacity: space space

Adjusted (Yes or No): space

Certified Standard Applied: checkbox lb ( )
kg ( )
checkbox lb ( )
kg ( )
checkbox lb ( )
kg ( )
checkbox lb ( )
kg ( )
checkbox lb ( )
kg ( )
Reading:
After Adjustments:

Comments: space
space
space

Monthly Scale Check

Date: space Last Date Serviced: space

Scale Reading: Test Weights
blank 20 kg 40 kg 60 kg 80 kg 100 kg
Add sequentially
(blank to 100 kg)
Remove sequentially
(100 kg to blank)

Pan Scale Verification

Test Weights 200 g 500 g 1 kg 5 kg 10 kg 20 kg
Scale Reading:

Conducted by: space

Checked by: space

Date modified: