PASCO PS-2195 Salinity Sensor - Manual (Page 5)

®
Model No.PS-2195 Specifications
5
More About Calibration
You can also calibrate the Salinity Sensor using a standard salinity solution purchased
from a company such as Hach (www.hach.com) or Lamotte (www.lamotte.com) that
offers water quality testing equipment. A third way is to make a calibration solution
from “Instant Ocean
® Sea Salt” (www.instantocean.com) which can be purchased at
most aquarium supply stores.
Total Dissolved Solids (TDS) and Conductivity
Total dissolved solids (TDS) is a measure of the amount of mineral and salt impurities
in a sample of water. TDS is usually measured in parts per million (ppm) and drinking
water is typically below 500 ppm. For example, one kilogram of water containing 1
milligram of dissolved solids has a TDS of 1 ppm. One way to measure the amount of
TDS in a sample is to measure the electric conductivity of the sample.
A conversion factor is used to convert conductivity to the approximate concentration
of TDS. The conversion factor depends on the specific dissolved solids and can vary
between 0.40 and 0.96, depending on the dissolved solids. A value of 0.65 is used as
an approximation if the dissolved solids are not known. As an example,
TDS (ppm) = 0.65 x Conductivity (
S). Since conductivity varies with temperature,
the Salinity Sensor has built-in compensation for temperature.
Table: Conversion Chart to Estimate TDS of Aqueous Solutions at 25 °C
Specifications
(*with calibration)
Conductivity
( S)
Parts per Million
As Ion As CaCO
3
As NaCl*
1.000 0.650 0.500 0.400
1.250 0.813 0.625 0.500
1.667 1.083 0.833 0.667
2.500 1.625 1.250 1.000
5.000 3.250 2.500 2.000
10.000 6.500 5.000 4.000
20.000 13.000 10.000 8.000
40.000 26.000 20.000 16.000
80.000 52.000 40.000 32.000
158.730 103.175 79.635 63.492
312.500 203.125 156.250 125.000
625.000 406.250 312.500 250.000
1250.000 812.500 625.000 500.000
2500.000 1625.000 1250.000 1000.000
5000.000 3250.000 2500.000 2000.000
10000.000 6500.000 5000.000 4000.000
Measurement Ranges Other Values
Conductivity 1,000 to 100,000 S Sample rate (maximum) 50 Hz
Temperature 0 to 50 degrees C Temperature compensation ±0.5 ppt from 0 to 45 °C at 33 ppt
Salinity 1 to 55 ppt ±1%* Cell constant 10X