Delta OHM HD3406.2, Руководство пользователя, Страница: 14 / 44

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Cells with temperature sensor
All probes are fitted with a built-in Pt100 or Pt1000 temperature sensor: the simultaneous measure-
ment of conductivity and temperature allows automatic correction of the effect of the latter on the
solution conductivity.
Choosing the cell constant
The constant is a piece of information which characterizes the cell. It depends on its geometry and
is expressed in cm
–1
. There is no cell capable of measuring the entire conductivity scale accurately
enough. Consequently, cells with different constants are used allowing exact measurements on dif-
ferent scales. The cell with constant K = 1cm
–1
allows measurements from low conductivity up to
relatively high conductivity.
The theoretical measurement cell is made of two 1cm
2
metallic plates separated one from the other
by 1cm. This type of cell has a cell constant Kcell of 1cm
–1
. In essence, the number, form, material
and dimensions of the plates are very different from model to model, from manufacturer to manu-
facturer.
The low constant K probes are preferably used for low conductivity values, the high constant ones
for high values.
The indicative measurement range is reported in the following diagram:
Automatic or manual conductivity compensation
The conductivity measurement refers to a standard temperature, called reference temperature
T_REF: that is, the instrument proposes the conductivity you would get if the temperature were
T_REF. This temperature could be 20°C or 25°C according to the setting in the T_REF menu item.
The conductivity increase per each grade of temperature variation is a characteristic of the solution
and is indicated by the term "temperature coefficient
α
T
": admissible values from 0.00 to 4.00%/°C,
default value 2.00%/°C.
When a combined probe with temperature sensor is present, the instrument automatically applies
the temperature compensation function, and proposes the measurement using the reference tempera-
ture T_REF according to the coefficient
α
T
on the display.
In absence of the temperature probe, the lower display shows the manually set compensation tem-
perature (default=25°C).
To point this condition out, the °C or °F symbol blinks intermittently near the temperature value.
On the main display an "
m " ( m anual) is turned on near the battery symbol (if on). The MT indica-
tion is printed on the print-outs. On the other hand, if the temperature probe is present, the AT sym-
bol appears.