halstrup-walcher P29, Оригинальное руководство пользователя

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P29 Instruction Manual
14
4.5 Readout of volume, mass flow and flow velocity
With square-root extracted output signal, the assignment of differential pressure volume, mass
flow or flow velocity can be set via the serial interface with a PC software or, for instruments
with display, via the menu using the four keys in the top cover.
The calculation of the analogue output and the display (for instruments with display) is done
according to the following formulas:
Calculation of the analogue output 0 - 20 mA or 4 - 20 mA:
𝐼
𝑜𝑢𝑡
=
20 𝑚𝐴
√Δ𝑝
𝑚𝑎𝑥
⋅ √Δ𝑝 𝐼
̇
𝑜𝑢𝑡
= 4 𝑚𝐴 +
16 𝑚𝐴
√Δ𝑝
𝑚𝑎𝑥
⋅ √Δ𝑝
Calculation of the analogue output 0 - 10 V:
𝑈
𝑜𝑢𝑡
=
10 𝑉
√Δ𝑝
𝑚𝑎𝑥
⋅ √Δ𝑝
Calculation of the display for volume flow, mass flow or flow velocity:
𝑉̇ =
𝑉̇
𝑚𝑎𝑥
√Δ𝑝
𝑚𝑎𝑥
⋅ √Δ𝑝 ̇ 𝑚̇ =
𝑚̇
𝑚𝑎𝑥
√Δ𝑝
𝑚𝑎𝑥
⋅ √Δ𝑝 ̇ 𝑣̇ =
𝑣̇
𝑚𝑎𝑥
√Δ𝑝
𝑚𝑎𝑥
⋅ √Δ𝑝
Thereby is:
Δ𝑝
the (internal) measured value for the differential pressure (in the selected unit, e.g.
Pa)
Δ𝑝
𝑚𝑎𝑥
the (adjustable) scaling end value of the differential pressure =
"Scale Top" (in the selected unit, e.g. Pa).
"Scale Bottom" must always be 0 when the output is square-rooted.
Δ𝑝
𝑚𝑎𝑥
, for example, is the differential pressure value generated by a dynamic
pressure probe at volume flow
𝑉̇
𝑚𝑎𝑥
𝐼
𝑜𝑢𝑡
Analog current output signal (0 - 20 mA or 4 - 20 mA)
𝑈
𝑜𝑢𝑡
Analog voltage output signal (0 - 10 V)
𝑉̇
𝑚𝑎𝑥
the (adjustable) volume flow value to be displayed at a differential pressure of
Δ𝑝
𝑚𝑎𝑥
= "Vol. flow. at max. scaling value" (in the selected unit, e.g. m³/h)
𝑉̇
the displayed volume flow value (in the selected unit, e.g. m³/h)
𝑚̇
𝑚𝑎𝑥
the (adjustable) mass flow value to be displayed at a differential pressure of
Δ𝑝
𝑚𝑎𝑥
=
"Mass flow” at max. scaling value" (in the selected unit, e.g. kg/s)
𝑚̇
the displayed mass flow value (in the selected unit, e.g. kg/s)
𝑣̇
𝑚𝑎𝑥
the (adjustable) flow velocity value to be displayed at a differential pressure of
Δ𝑝
𝑚𝑎𝑥
= "Flow rate” at max. scaling value" (in the selected unit, e.g. m/s)
𝑣̇
the displayed flow velocity value (in the selected unit, e.g. m/s)
In addition, a low flow suppression (LFV) can be set as a percentage of the nominal pressure
range. If the measured pressure value falls below this limit, the output is set to zero. This
avoids strongly fluctuating (square-rooted) output values at very small pressure measuring
values.