9
8850-3 Conductivity/Resistivity Transmitter
Parts Per Million (PPM) Factor
This feature is only applicable when PPM display units are selected. The programmable PPM Factor is adjustable from 0.01 to
3.00 (factory default = 2.00).
Determine the best PPM Factor for a process solution by calculating the solution's conductivity (
μ
S) and the percent of total
dissolved solids (PPM).
PPM Factor = Solution conductivity (
μ
S/cm)
Total dissolved solids (PPM)
TDS (PPM) =
Solution conductivity (
μ
S/cm)
PPM Factor
Example:
• Solution conductivity = 400
μ
S/cm
• TDS = 200 PPM (mg/L)
PPM Factor = 400
μ
S/cm =
2.00
200
PPM
Temperature Coeffi cient
Conductivity measurement is highly dependent on temperature. Temperature dependence is expressed as the relative change per °C,
commonly known as percent/°C change from 25 °C, or slope of the solution.
Slopes can vary signi
fi
cantly depending on process solution type. The factory default temperature compensation factor is 2.00%/°C.
Process solutions may require adjustment for maximum accuracy. To determine the optimum temperature compensation factor for a
process:
1.
Disable the 8850 temperature compensation % factor by entering 0.00.
2.
Heat the sample solution close to the maximum process temperature. Place sensor in the sample solution allowing several
minutes for stabilization. Access the VIEW menu and record the displayed temperature and conductivity values in the spaces
provided:
Displayed temperature:
T1 = _______ °C
Displayed conductivity:
C1 = _______
μ
S
(Do not use this procedure for solutions from 0.055
μ
S to 0.1
μ
S (10 M
to 18 M
). An internal pure water curve is used for these
ranges. The factory default setting of 2.00%/°C should be used.)
3.
Cool the sample solution close to the minimum process temperature. Place sensor in the sample solution allowing several
minutes for stabilization. Record displayed temperature and conductivity values in the spaces provided:
Displayed temperature:
T2 = _______ °C
Displayed conductivity:
C2 = _______
μ
S
(A 10% change in conductivity between steps 2 and 3 is recommended.)
4.
Substitute recorded readings (steps 2 and 3) into the following formula:
TC Slope = 100 x (C1 - C2)
(C2 x (T1 - 25)) - (C1 x (T2 - 25))
Example: A sample solution has a conductivity of 205
μ
S @ 48°C. After cooling the solution, the conductivity was measured at
150
μ
S @ 23 °C. (C1 = 205, T1 = 48, C2 = 150, T2 = 23)
The TC is calculated as follows:
TC Slope = 100 x (205 - 150) = 5500 =
1.42%/°C
(150 x (48 - 25)) - (205 x (23 - 25)) 3860
