Hach Polymetron 9526 Manual Básico Del Usuario página 9

thermometer on the whole loop at a temperature of approximately 20 °C. The temperature
measurement is therefore fully calibrated.
The product also uses an accurate temperature compensation algorithm taking account of the pure
water dissociation and of any components such as NaCl or HCl. By default, the NaCl curve is
activated into the system as it is representative of the majority of impurities present in pure water.
Finally, in order to comply with the USP standard, it is possible to easily deactivate any temperature
compensation curve during operation. Conductivity and resistivity measurements are then no longer
referenced to a given temperature (25 °C in general).
Accurate determination of the cell constant
The conductivity of pure water should be accurately identified. As there are no reliable low
conductivity calibration solutions, the measurement of pure water conductivity must be performed by
comparison with a reference system in compliance with the prevailing standards.
The conductivity sensor integrated in the Polymetron 9526 has a cell constant K that has been
accurately (± 2%) defined in our factory, with water having a conductivity < 10 μS/cm, and by
comparison with a reference conductivity sensor whose constant complies with the ASTM D
1125 standard (with NIST traceability by using a certified precision thermometer).
The 9526 is therefore a reliable standard allowing the certification of other in-line sensors, when the
sample taken is representative of the process (flow rate, composition and temperature).
Optimized design
When starting the sampling, the sample tube, which is initially empty, may have some bubbles in it.
The same applies to the fluid that expands or heats up in the measurement cell. Air bubbles on the
electrode will reduce the active surface, leading to a non-representative low conductivity value (high
resistivity).
The 9526 flow chamber contains no protrusions or dead zones and has been designed to avoid air
bubble retention. Its conductivity sensor, used only for measurements in ultra pure water, has
electro-polished electrodes that also prevent the retention of air bubbles. A minimum flow rate of
20 L/h (ideally 60 L/h) is required in order to facilitate the extraction of air bubbles but also to obtain a
temperature that is identical to that of the process sample. It is important that the sampling system
does not pollute the sample being analyzed (no contamination with ambient air or impurities).
After being carefully calibrated in our facility, the 9526 is operated for 30 minutes in ultra pure water
(grade 1 and ISO 3696/BS3978) before being protected by plugs to avoid any contamination of the
conductivity cell. Sample connections are designed to meet the requirements of pure and ultra pure
water sampling.
Calibration guidelines
As stated in the ISO 100012-1 Standard, a time period should be defined between each system
calibration. Hach Lange can perform this operation in our facility to guarantee traceability to national
certified standards.
In order to meet technical specifications as closely as possible, Hach Lange recommends calibrating the
9526 once a year in our facility to guarantee the validity of the certification for one year, if and only if, important
components of the unit have not been modified or accessed in any way. A system of seals is placed on each
component of the unit to validate this.
Installation
Multiple hazards. Only qualified personnel must conduct the tasks described in this section of the
document.
N O T I C E
C A U T I O N
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