Calibration Procedure
1.Requirements
The
A) Calibration with NIST Traceable Solutions:
When using NIST traceable standards, ensure the sensor and test solution are at the solution temperature specified on the test solution label. Prevent contamination of the calibration solution. Thoroughly rinse the sensor in a small amount of test solution before placing in any test solution for calibration purposes.
B) Optional Verification with Precision Resistors:
The use of precision resistors (±0.1%) connected to the rear "Temp In", "Signal IN", and "Iso Gnd" terminals in place of the sensor, yields quick and accurate electronic instrument calibration. Calibration is completed as follows:
1)Select a standard cell constant based on desired range of operation.
2)Place a 1096 Ω (25°C) resistor between "Temp IN" and "Iso. Gnd" terminals as shown. Note: Temperature simulation errors can adversely effect calibration: 3.85 per °C.
3)Calculate the required simulation resistor that represents a value within the selected cell range. The formula for determining the required simulation resistance is:
9Iso. Gnd (BLACK)
8 | Temp. IN |
|
|
|
|
|
| |
(WHITE) | TC resistor | |||||||
|
| |||||||
7 | (RED)Signal IN |
|
|
|
|
|
| |
Simulation resistor | ||||||||
|
| |||||||
Resistance | = |
|
| Sensor Cell |
| : | e.g. |
| 0.1 Cell | = 5,000 Ω or 5 KΩ | ||
Desired conductivity (Siemens*) |
| 0.000020 (Siemens*) | ||||||||||
|
|
|
|
| ||||||||
Conductivity | = |
|
| Sensor Cell |
| : |
| e.g. |
| 0.1 Cell |
| = 0.000001 Siemens* |
|
|
|
|
| ||||||||
|
|
|
| Simulation resistance (Ω) |
|
|
|
| 100,000 (Ω) | or 1∝S/cm | ||
(*Conversion: 1 ∝S = 1 X
4)Place the calculated simulation resistance between the "Signal IN" and "Iso Gnd" terminals as shown.
5)Set temperature and set conductivity. (Optional: Reset to factory calibration by entering zero as the "Set Conductivity" value.)
2.Temperature Coefficient
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 very significantly 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 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 = _______ °C |
(Do not use this procedure for solutions from 0.055 ∝S to 0.1 ∝S (10 MΩ to 18 MΩ). 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 = _______ °C |
(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 ∝S
@48°C. After cooling the solution, the conductivity was measured at 150 ∝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 |
| |
page 16