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AQUALAB TDL/TDL 2
4. SERVICE
This section describes the calibration and maintenance of the AQUALAB TDL.
Troubleshooting solutions and customer service information are also provided.
4.1 VERIFICATION AND CALIBRATION
It is important to verify the AQUALAB TDL water activity calibration against known
standards to guarantee optimal performance and accuracy. METER recommends
verification or once per shift or daily before use.
METER also recommends annual factory calibration to maintain optimal performance.
4.1.1 WATER ACTIVITy VERIFICATION
The AQUALAB TDL uses the tunable diode laser technique to determine water activity. The
components used by the instrument to measure water activity are subject to contamination,
which may affect AQUALAB TDL performance. Therefore, frequent verification assures that
the AQUALAB TDL is performing correctly. In addition, providing a linear offset can be used to
overcome any additional instrument drift.
VERIFICATION STANDARDS
Verification standards are specially prepared, unsaturated salt solutions having a specific
molality and water activity value that are accurately measurable. The verification standards
sent with the initial shipment are very accurate and available from METER. Using verification
standards to verify accuracy can greatly reduce preparation errors. Verification standards
come in seven water activity levels: 1.000, 0.984, 0.920, 0.760, 0.500, 0.250, and 0.150 (
).
The standards are produced under a strict quality assurance regime.
Table 3 Verification standards
Verification Standard at 25 °C
a
w
17.18 mol/kg LiCl
0.150 ±0.005
13.41 mol/kg LiCl
0.250 ±0.003
8.57 mol/kg LiCl
0.500 ±0.003
6.00 mol/kg NaCl
0.760 ±0.003
2.33 mol/kg NaCl
0.920 ±0.003
0.50 mol/kg KCl
0.984 ±0.003
Steam Distilled Water
1.000 ±0.003
NOTE: Safety Data Sheet (SDS) for these standards are available at
To use a verification standard, remove the twist top and puncture the foil cap. Pour the
contents into a sample cup.
NOTE: To avoid inaccurate water activity readings, verification standards should be used once immediately after
opening. Do not store standards in sample cups for repeated use.
