ASTM D4308 Test Method for Electrical Conductivity of Liquid Hydrocarbons by Precision Meter
9. Preparation of Apparatus
9.1 Cleaning the Cell - The cleaning procedure to be used depends on the estimated conductivity of the sample to be tested.
9.1.1 For samples that are expected to exhibit conductivities below 1 pS/m, the KSLA cell should be completely disassembled, the parts cleaned and the cell reassembled using protective gloves.
9.1.1.1 Dismantle the cell by removing the loose battery cap, the outer electrode electrical connector and the bottom screw-on cap. Press the inner electrode towards the bottom of the outer electrode and remove the inner electrode TFE-fluorocarbon insulator assembly.
9.1.1.2 Each part of the cell should be rinsed thoroughly five times with cleaning solvent followed by rinsing with treated n-heptane. The parts should be dried with a stream of nitrogen gas.
9.1.1.3 After reassembly, the cell should be rinsed with treated n-heptane.
9.1.1.4 After cleaning, check the cleanliness of the cell by measuring the conductivity of treated n-heptane in accordance with Section 11. The corrected value should be lower than 0.05 pS/m.
9.1.2 For samples that are expected to exhibit conductivities above 1 pS/m, the KSLA cell still assembled should be rinsed five times with cleaning solvent, followed by rinsing with treated n-heptane. The cell should be dried with a stream of nitrogen gas.
9.1.2.1 After cleaning, check the cleanliness of the cell by measuring the conductivity of treated n-heptane in accordance with Section 11. The corrected value should be lower than 0.1 pS/m.
9.2 Cleaning ofAuxiliary Equipment:
9.2.1 Pipets used to transfer samples should be rinsed inside and outside with cleaning solvent using a non-contaminating squeeze bottle, then blown dry with clean, dry nitrogen. Thermometers should be similarly rinsed and maintained.
NOTE 5 - If a cell has been used to test samples of high-conductivity, that is, more than 1000 pS/m, it should be disassembled for thorough cleaning. Very thorough cleaning may also be accomplished by placing the disassembled cell in a Soxhlet apparatus containing boiling toluene/isopropyl alcohol for several hours.
NOTE 6 - If testing is to be done on both low-conductivity (<1 pS/m) and high-conductivity (>1000 pS/m) samples, separate cells are recommended.
10. Calibration and Standardization
10.1 Checking the Test Equipment:
10.1.1 Remove cell and cable from the meter.
10.1.2 Depress the 20 pS/m switch. The digital reading should indicate 0.00 +/- 0.01 pS/m after 3 s. If readings exceed +/- 0.01 either adjust zero or record the zero error for calculating final report value.
10.1.3 Depress the calibrate switch. The digital reading should indicate 1000 +/- 3 pS/m.
10.1.4 If low battery indicator is displayed during measure or calibration, the internal batteries should be replaced.
10.2 Checking the Cell Constant:
10.2.1 A check on the cell constant is necessary only if the cell has been damaged. Two capacitance measurements are required with a precision ac bridge. Make a rigid two-terminal connection between the cell assembly and the bridge. Measure the total capacitance, CE (picofarad) of the empty assembly. Without disturbing the connection, add 100 mL of a hydrocarbon standard and measure the new total capacitance, CS (picofarad) and the temperature in the cell. Alternatively, the cell can be sent to the manufacturer for recalibration.
10.2.2 Calculate the actual capacitance, CA, of the empty cell as follows:
CA = (CS - CE)/(k - 1)
where:
k = dielectric constant of the hydrocarbon at test temperatures.
10.2.3 Calculate the cell constant as follows:
K = 8.854/CA
10.2.4 The cell constant of a new KSLA cell is 1.0. Because of its configuration, the cell constant cannot change significantly unless there is gross damage.
