Measurement Uncertainty

 

 

Measurement Uncertainty for VGT Accredited Test Methods

When scientists make a measurement or calculate some quantity from their data, they generally assume that some exact or "true value" exists based on how they define what is being measured (or calculated).  Scientists reporting their results also calculate a range of values that they expect this "true value" to fall within, based on expected errors associated with that measurement.  This range is called the Measurement Uncertainty and is assessed at a particular result value. 

When assessing whether a result is within compliance or not, it may be necessary to take account of the measurement uncertainty range that the result reported may fall into.  As an example, if a Total Suspended Solids result is reported as 50 mg/L, the measurement uncertainty associated with that result has been calculated as ±2 mg/L, then it is possible that the “true value” is somewhere between 48 and 52 mg/L.

The measurement uncertainty for VGT’s accredited tests is given below.  For further information, please contact the laboratory.

 

 Test

 Method ID

 Level MU Assessed 

 Measurement Uncertainty (MU) (+/-) 

 Including Sampling (+/-) 

 pH

 VGT WI01

 APHA 4500 H-B 

7.00

0.01

Creeks: 0.01

Dams: 0.04

Groundwaters: 0.1

 Conductivity

 VGT WI02

 APHA 2510B

1412

10

Creeks: 15

Dams: 20

Groundwaters: 27

 Solids - Total suspended (TSS)

 VGT WI03

 AS3550.4

50

2

 

 Solids - Total dissolved (TDS)

 VGT WI49

 AS3550.4

746

10

 

 Turbidity

 VGT WI04

 APHA 2130B

20

0.2

 

 Dissolved oxygen (DO)

 APHA 4500O-G 

8.8

 

0.2

 Oil and grease

 APHA 5220B

10

1

 

 Biochemical oxygen demand (BOD)

 APHA 5210B

198

4

 

 Particulate matter - PM2.5;

 Particulate matter - PM10;

 Suspended particulate matter – Total 

 VGT WI44

 

50

 

2

 

 Ash;

 Combustible matter;

 Solids - Insoluble

 VGT WI14

 AS3580.10.1

4

0.8

 

 

 

References:

Nordtest Guides:

Eurachem Guides: