Measured value correction and compensation
11.2.5 Temperature compensation
Sensors whose measured values depend heavily on the temperature of the
measuring medium usually incorporate their own temperature sensor and per-
form temperature compensation automatically; (see Section 12.3.9Measuring
range list ´with TC´). However, dynamic pressure probes and pH probes are
also available without their own temperature sensor. If the temperature of the
medium deviates from 25°C the following measuring errors must be considered
e.g. Error per 10 °C:
Compensation range
Sensor
Dynamic pressure approx. 1.6 %
-50 to 700 °C
NiCr-Ni
pH probe approx. 3.3 %
0 to 100 °C
NTC or Pt100
Compensation at constant temperature can be activated via function
Temp
comp.
e.g. in the menu
Measured value correction
:
Enter the compensation temperature in function
Temp.comp: CT 31.2 °C
Continuous temperature compensation with external temperature sensors can
be activated either via the reference channel of the sensor to be compensated
or by configuring any temperature sensor as reference sensor with a ´
*T
´ in the
designation; (see 10.3.2) :
While the temperature is being measured, point T flashes.
Temp.comp. CT 23.5 °C
Automatic temperature compensation can be switched off by pro-
gramming the reference channel for the measuring point to itself.
11.2.6 Atmospheric pressure compensation
Some measured variables depend on the ambient atmospheric pressure (see
Section 12.3.9 Measuring range list ´with PC´) with the effect that large devia-
tions from normal pressure (1013 mbar) may lead to measuring errors.
e.g. error per 100 mbar
Compensation range
Rel. humidity psychrometer approx. 2 %
500 to 1500 mbar
Mixture ratio, capacitive
approx. 10 %
Vapor pressure VP up to 8 bar
Dynamic pressure
approx. 5 %
800 to 1250 mbar (error < 2 %)
O2 saturation
approx. 10 %
500 to 1500 mbar
It is advisable therefore, especially when taking measurements at appreciable
heights above sea level to take due account of the atmospheric pressure (ap-
prox. -11 mbar / 100 m above mean sea level, MSL). This can be programmed
(see 12.5.6) or it can be measured using a suitable sensor (reference sensor
with designation ´*P´, see Manual 6.7.2).
The function
Atmospheric pressure
can be integrated into any user menu or be
set in the standard menu
Device Configuration
.
Enter atm. pressure in the function Atm. pressure
Atmosph. pressure CP 1013 mbar
ALMEMO
®
5690-2M
35
