US Environmental Protection Agency
Office of Pesticide Programs

Office of Pesticide Programs

Microbiology Laboratory

Environmental Science Center, Ft. Meade, MD

Standard Operating Procedure for
Calibration and Maintenance of Weigh Balances

SOP Number: EQ-03-07
Date Revised: 01-29-14

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SOP No. EQ-03-07
Date Revised 01-29-14
Page 1 of 6

SOP Number

EQ-03-07

Title

Calibration and Maintenance of Weigh Balances

Scope

Describes process for use, calibration, and quality control of weigh
balances and reference weights.

Application

Weigh balances are used to measure the weight of objects in the
laboratory, such as media and reagent ingredients and disinfectant
containers. Reference weights are used as reference standards to
verify the calibration of the weigh balances.





Approval Date

SOP Developer:



Print Name:

SOP Reviewer



Print Name:

Quality Assurance Unit



Print Name:

Branch Chief



Print Name:





Date SOP issued:



Controlled copy number:



Date SOP withdrawn:

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SOP No. EQ-03-07
Date Revised 01-29-14
Page 2 of 6

TABLE OF CONTENTS
Contents	Page Number

1.

DEFINITIONS

3

2.

HEALTH AND SAFETY

3

3.

PERSONNEL QUALIFICATIONS AND TRAINING

3

4.

INSTRUMENT CALIBRATION

3

5.

SAMPLE HANDLING AND STORAGE

3

6.

QUALITY CONTROL

3

7.

INTERFERENCES

3

8. NON-CONFORMING DATA

3

9.

DATA MANAGEMENT

3

10.

CAUTIONS

4

11.

SPECIAL APPARATUS AND MATERIALS

4

12.

PROCEDURE AND ANALYSIS

4

13.

DATA ANALYSIS/CALCULATIONS

6

14.

FORMS AND DATA SHEETS

6

15.

REFERENCES

6

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SOP No. EQ-03-07
Date Revised 01-29-14
Page 3 of 6

1. Definitions

1.	ISO = International Organization for Standardization

2.	Tolerance for weigh balances = Acceptable limits or range in
measurement (in grams) that the laboratory can tolerate. See 12.4.

2. Health and
Safety

None

3. Personnel
Qualifications
and Training

Refer to SOP ADM-04, OPP Microbiology Laboratory Training.

4. Instrument
Calibration

1.	Weigh balances are inspected, cleaned and calibrated annually by an ISO
17025 accredited vendor.

2.	Calibration of the reference weights is performed every two years by an
ISO 17025 accredited vendor. Weights may be calibrated more frequently
if deemed necessary (e.g., weight is dropped, chipped, etc.).

5. Sample

Handling and
Storage

1.	Wear clean cotton gloves (supplied with reference weights) or use forceps
while handling reference weights. To avoid depositing oil and dirt onto the
surface of the weight, do not touch weights with bare hands.

2.	Store reference weights in cases provided by the manufacturer.

6. Quality Control

For quality control purposes, the required information is documented on the
appropriate form(s) (see section 14).

7. Interferences

1.	For optimal performance, place balance on a stable, even, horizontal
surface with minimal vibration. Avoid areas with excessive heat and
moisture, direct sunlight, aggressive chemical vapors, and drafts.

2.	If a balance is transferred to a different location, the accuracy check
(section 12.3) must be performed prior to use in the new location.

8. Non-
conforming
Data

1.	When verifying the calibration of weigh balances (section 12.3), any
discrepancies in weight measurements will be confirmed by repeating the
operation. A service representative will be notified, if necessary, to re-
calibrate the instrument when the calibration check shows that the weigh
balance is outside of the acceptable tolerance range (see section 12.4).

2.	If the vendor determines that a weigh balance or reference weight is out of
tolerance and cannot be properly calibrated, the equipment will be
replaced.

3.	Procedures will be consistent with SOP ADM-07, Non-Conformance
Reports.

9. Data

Management

1. An inventory of weigh balances and reference weights requiring vendor
calibration will be maintained electronically (see section 14). After each

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SOP No. EQ-03-07
Date Revised 01-29-14
Page 4 of 6



addition to or deletion from the inventory, file a hard copy of the
inventory in the Weigh Balance Calibration Record book.

2. Data will be archived consistent with SOP ADM-03, Records and
Archives.

10. Cautions

1.	Reference weights are removed from service when the calibration expires
(two years from the date of calibration) and are returned to service when
recalibration is completed.

2.	Annual calibration of weigh balances is performed at approximately the
same time each year.

3.	See section 5 for guidance on proper handling of reference weights.

11. Special

Apparatus and
Materials

1.	Weigh balances. Used to measure the weight of objects in the laboratory,
such as media and reagent ingredients and disinfectant containers.

2.	Reference weight set (range of lg to 50g) and Individual reference
weights (1 mg, 10 mg, 100 mg, 100 g, 500 g, 1 kg, 2 kg). Used as
reference standards to verify the calibration of the weigh balances.

12. Procedure and
Analysis

Calibration certificates must contain the stamp of the accrediting body (e.g.,
A2LA, NVLAP) and the calibration vendor certificate number.

12.1 Calibration of
Weights

a.	Before the calibration of a weight or weigh set expires (two years
from the date of calibration), remove it from service.

b.	Consult ISO 17025 accredited vendor regarding quote for service,
packing/shipping instructions, and completion of any required forms
prior to shipping weights.

c.	Pack and ship weights to vendor.

d.	Once the weight or weight set has been recalibrated and shipped back
to the laboratory, file the calibration certificate in the Weigh Balance
Calibration Record book and return the weights to service.

12.2 Daily

Calibration and
Use of Weigh
Balances

a.	Follow the instructions provided by the manufacturer for the
operation of each weigh balance. See section 15.

b.	Each balance has a built-in calibration system.

c.	When weighing, apply load to center of balance. Close balance
doors, if applicable, to reduce draft.

d.	Clean balance pan after each use with a soft brush or damp towel.
Allow the balance to dry before the next use.

12.3 Six Month
Accuracy

a. Check each weigh balance, approximately six months following
vendor calibration, for accuracy using reference weights.

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SOP No. EQ-03-07
Date Revised 01 -29-1 4

Page 5 of 6

Check of
Weigh

Balances

b.

See the Reference Weight Selection for Sixih Month Aceuiaey

Check (section 14) for guidance on which reference weights to use to
verify the calibration of each weigh balance.



c.

See section 5 for guidance on handling reference weights.



d.

Tare or "zero" the weigh balance before the addition of each weight.



e.

Add weights to center of balance and close balance doors, if
applicable.



£

Record results for each reference weight on the Verification of
Weigh Balance Calibration Record Form (section 14).



g-

See section 12.4 for acceptable tolerances for weigh balances when
conducting the accuracy check.



h

Note that the acceptable tolerance varies for the 10 and 100 nig
reference weights, depending upon whether they are being weighed
on a top loading balance that reads to 0.0lg or a more sensitive
analytical balance.

12.4 Six Month

Accuracy
Cheek of

Weigh
Balances -



Total Load
Applied to Weigh
Balance

Acceptable Tolerance

Acceptable Range of
Weigh Balance
Readings





1 nig

± 0.00005 g

0.00095 g to 0.00105 g



Acceptable
Tolerances



10 mgA

± 0.0005 g

0.0095 g to 0.0105 g





10 mgB

None^

0.01 g







~~ [00 ulgA

± 0.005 g

0.095 g to 0.105 g







100 mgB

±0.01 g

0.09 g to 0.11 g







1 g

± 0.01 g

0.99 g to 1.01 g







2 g

±0.01 g

1.99 g to 2.01 g







5 g

±0.01 g

4.99 g to 5.01 g







10 g

±0.01 g

9.99 g to 10.01 g







20 g

± 0.01 g

19.99 g to 20.01 g







50 g

± 0.01 g

49.99 g to 50.01 g







100 g

±0.1 g

99.9 g to 100.1 g







150 g

±0.1 g

149.9 g to 150,1 g







500 g

± 0.1 g

499.9 g to 500.1 g

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SOP No. EQ-03-07
Date Revised 01-29-14
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1kg

±1.0g

999 g to 1001 g







2 kg

±1.0g

1999 g to 2001 g







3 kg

±1.0g

2999 g to 3001 g







4 kg

±1.0g

3999 g to 4001 g







5 kg

±1.0g

4999 g to 5001 g







AWhen weighed on an analytical balance.









BWhen weighed on a top loading balance that reads to O.Olg.



12.5 Annual

Calibration of

Weigh

Balances

a.	Contact ISO 17025 accredited vendor and schedule a date for
calibration.

b.	Weigh balances are not shipped out. The vendor inspects, cleans, and
calibrates balances on site.



c. File the calibration certificate in the Weigh Balance Calibration
Record book.



13. Data Analysis/
Calculations

None

14. Forms and Data

Forms are stored separately from the SOP under the following file names:



Sheets

Sample Inventory of Weigh Balances and EQ-03-07_Fl.docx
Reference Weights Requiring Vendor Calibration





Reference Weight Selection for Six Month
Accuracy Check

EQ-03-07_F2.docs





Verification of Weigh Balance Calibration
Record Form

EQ-03-07_F3.docx



15. References

Operation manuals for weigh balances located in file cabinet in D-wing.

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