Hiệu chuẩn máy conductivity
Hiệu chuẩn máy conductivity
GENERAL CALIBRATION PROCEDURE
- Scope of procedure
Calibration of all Conductivity Meter.
- Equipment Required
- Calibrated Conductivity Buffer Solutions
- Calibrated Temperature Standard
- Wires, Hoses, Adapters, Fittings, Sterile Tubes
- Cleaning supplies: DI Water, Alcohol Wipes, Paper Towels, Latex Gloves
- Safety Glasses or Face Shield, Lab Coat.
- Functional Inspection
- Visually inspect the Unit Under Test (UUT) for obvious damage that may affect accuracy and/or operation and note any observations.
- Clean the UUT as necessary to avoid cross contamination to yourself or other instruments.
- If necessary, turn on the UUT to check for function and allow for proper warm-up time.
- For a system calibration, with moving components, inspect all related parts for signs of damage.
- If the functional inspection passes proceed to the calibration process.
- Test Point Selection
- Special instructions and specific test points required by the customer must be followed if such instructions are available.
- Unless otherwise specified, select 2 test points at low and high values: 1 test point in μS/cm units and 1 test point in S/m.
- If the UUT is a Calibration Standard, select at least 3 test points of uS, mS and S units.
- If possible, find the cell constant value the UUT is set at and make note of this number.
Customer required tolerances are to be used for all calibrations unless otherwise noted. If the customer does not supply instrument tolerances the manufacturing specifications or other approved sources are to be used as the default.
If no tolerances can be found the UUT shall be given an accuracy of +/- 2% of reading.
- Follow all safety procedures as required prior to performing any calibrations.
- Ensure all calibration standards used to perform calibration are at least 4 times more accurate than the UUT, if possible, and have valid certifications and have had the proper warm-up time.
- Make sure the proper environmental conditions have been met and record the values.
- Set all equipment switches and/or controls to the proper position(s) before making connections or applying power prior to beginning the calibration process unless designated otherwise.
- Attach the proper accessories, wires, fittings and adapters as necessary.
- If possible, set the UUT to measure in Manual Temperature mode of 25o If this cannot be done a temperature compensation calculation must be made in order to record the proper values. With the UUT set to automatic temperature compensation mode the calculated conductivity value will be shown on the display. The same calculation must be made to the calibrated buffer solution in order to make the correct comparison.
- For some industrial devices a Cell Constant and Temperature factor is written either on the sensor wiring or body and must be entered into the meter. Make sure these values match what is programmed into the UUT prior to performing the calibration or an incorrect reading will be displayed.
- Place all buffers in sterile vials or other suitable container for testing.
- Carefully place the UUT electrode or sensor into the first test buffer and allow to stabilize.
- If a temperature compensation is to be calculated measure the temperature of the buffer solution with the calibrated temperature standard and apply the true value.
- Record the reading and continue to the next test point.
- For some devices electronic simulated calibrations can be made by attaching the proper wiring to the calibration simulator or calibrated decade and sourcing the UUT with the resistance scale.
- Note and record all readings from the Calibrated Standard and UUT, and verify all readings are within the specified limits.
- If possible, adjustments are to be made for all out of tolerance readings or readings that are more than 50% of the acceptable tolerances unless these adjustments cause the instrument to fail at other points.
- Conductivity adjustments can be made in either the unit value or the cell constant. The Cell Constant is a value that determines the unit range value. A low cell constant will display a low value (micro Siemens) and a high cell constant value will display a high value (Siemens). Typical Cell Constant values can range between 0.010 to 1.000.
- If any necessary adjustments are made note and record the new cell constant value for future references. The UUT must be re-tested at the required test points to ensure accuracy.