Measured value correction and compensation
14.3,14.4 ). Any D6 or D7 sensor whose measurable variables are affected by
ambient temperature or atmospheric pressure is already compensated internally
and its associated values are shown in the sensor display (s. 11.2.2).
11.2.1 Setting measured values to zeron
One very useful function is to zero the mea-
sured value at certain locations or points in time
to act as a reference value from which to ob-
serve subsequent deviations. Having selected
the measured value function the softkey
<ZERO>
will appear. Pressing this key saves the dis-
played measured value as
base value
and re-
sets it to zero (s. 15.7).
Select the '
Measured value
' function (s. 9.4):
00:
23.4
°C
To zero the measured value:
<ZERO>
The measured value should then show:
00: 00.0 °C
and symbol
REL
The base value is assigned measured value:
Base value: 23.4 °C
To cancel zero-setting, after selecting this function:
<ZERO>
press and hold down
If the function is locked (s. 15.4) the base value is not saved on the
plug but only
temporarily
to RAM where it is retained until the device
is next switched off. This status is indicated in the display by the
symbol
REL
; in other cases the symbol
º
appears.
If you prefer to disable the zero-setting function completely, the chan-
nel in question must be locked at level 6.
11.2.2 Atmospheric pressure compensation
Measured variables affected by ambient atmospheric pressure may, in the
event of substantial deviation from normal pressure (1013 mbar), be subject to
certain measuring errors.
e.g. error per 100 mbar:
Compensation range
Rel. humidity psychrometer approx. 2%
500to 1500 mbar
Mixture ratio, cap.
approx. 10 %
Vapor pressure VP up to 8 bar
Dynamic pressure
approx. 5%
800 to 1250 mbar
O
2
saturation
approx. 10%
500 to 1500 mbar
It is important therefore, especially when working at significant altitudes above
sea level, to take due account of atmospheric pressure (approx. -11 mbar / 100
meters above mean sea level, MSL).
Any D6 or D7 sensor whose measurable variables are affected by atmospheric
pressure incorporates its own atmospheric pressure sensor; this performs atmo-
spheric pressure compensation automatically. This value is normally available
as a measuring channel but it is also displayed in the menu
Sensor display
as
atmospheric pressure compensation for appropriate measurable variables.
A measured atmospheric pressure compensation can be displayed in menu
CP.
ALMEMO
®
204
27
00:
23.4
°C
Temperature REL
ZERO ESC F
Summary of Contents for ALMEMO 204
Page 72: ...20 Annex 72 ALMEMO 204...
