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7.4
Logarithmic
7.4.1
The Logarithmic output is an accurate output that can cover the entire range of the 7B or be used
with a selected range. To use this output, the user must select an exponent that corresponds to
10 V and the exponent that corresponds to 0 V. The exponent chosen for this format uses the
formula below to convert the output voltage into a pressure measurement. Note that H is the
exponent of the 10 V value and L is the exponent of the 0 V value. Volt is the analog output
voltage.
𝑆𝑆𝑂𝑂𝑉𝑉𝑆𝑆
=
10
H
−
L
𝑂𝑂𝑂𝑂𝑂𝑂𝑃𝑃𝑉𝑉𝑉𝑉
= 0
− 𝐿𝐿
𝑃𝑃𝑃𝑃𝑉𝑉𝑃𝑃𝑃𝑃𝑂𝑂𝑃𝑃𝑉𝑉
(
𝑇𝑇𝑉𝑉𝑃𝑃𝑃𝑃
) = 10
� 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉
𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆−𝑉𝑉𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑉𝑉�
7.4.2
For example, with the logarithmic range set to a 0 V value of 1*10
−
7
and a 10 V value of 1*10
−
3
and a voltage reading of 3.075 Volts, the pressure corresponds to:
𝑆𝑆𝑂𝑂𝑉𝑉𝑆𝑆
=
10
−
3
−
(
−
7) = 2.5
𝑂𝑂𝑂𝑂𝑂𝑂𝑃𝑃𝑉𝑉𝑉𝑉
= 0
−
(
−
7) = 7
𝑃𝑃𝑃𝑃𝑉𝑉𝑃𝑃𝑃𝑃𝑂𝑂𝑃𝑃𝑉𝑉
(
𝑇𝑇𝑉𝑉𝑃𝑃𝑃𝑃
) = 10
3
.
075
2
.
5 −7
= 1.7
∗
10
−6
𝑇𝑇𝑉𝑉𝑃𝑃𝑃𝑃
7.4.3
To select the Logarithmic output, navigate to the Analog Output screen, press ENT, and then use
the UP or DOWN arrow to select Logarithmic option. Press ENT to save the change. Press the
DOWN arrow to navigate to the 10 V exponent selection screen. Press ENT to unlock and then
the UP or DOWN arrow to select the value. Press ENT to save the value. Press the DOWN arrow
to navigate to the 0 V exponent selection screen. Press ENT to unlock the screen and the UP or
DOWN arrow to select the 0 V value.
