The refractometer calibration is verified using a set of standard refractive index liquids. In order to perform a valid verification, at least three liquids need to be used. The verification is valid only within the refractive index range defined by these three liquids.
The instrument automatically recognizes the following refractive index standard liquids (the values are stated at +25 °C):
- 1.3200
- 1.3300
- 1.3400
- 1.3500
- 1.3600
- 1.3700
- 1.3800
- 1.3900
- 1.4000
- 1.4100
- 1.4200
- 1.4300
- 1.4400
- 1.4500
- 1.4600
- 1.4700
- 1.4800
- 1.4900
- 1.5000
- 1.5100
- 1.5200
The accuracy of the certified standard refractive index liquids is ± 0.0002 and they can be traced back to NIST standards #1823 and #1823 II. As the specified accuracy of the refractometer is ± 0.0002, then the representative level is the sum of the two accuracy specifications, that is ± 0.0004.
Vaisala provides a set of standard R.I. liquids, PR‑2300, containing five selected liquids (1.3300, 1.3700, 1.4200, 1.4700, 1.5200). The set can be ordered from Vaisala. Other liquids are available on request.