Measuring Operations - Ahlborn ALMEMO 2590-2A Operating Instructions Manual

5. Introduction
Limit values and alarm
Per measuring channel two limit values can be set (1 maximum and 1 minimum).
In the event of one of these limit values being exceeded an alarm signal is output
and relay output modules actuate the associated alarm contacts; these can be
allocated individually to specific limit values. Hysteresis is set by default to 10
digits but this can be adjusted to any number between 0 and 99. The exceeding
of a limit value can also be used to automatically start or stop measured value
recording.
Sensor locking
All sensor data stored in the connector EEPROM can be protected by means of
a graduated locking function against undesired access.

5.1.2 Measuring operations

For each transducer 4 measuring channels are available; i.e. it is also possible
to evaluate double sensors, individually scaled sensors, and sensors with func-
tion channels. You can move forwards or backwards from one measuring chan-
nel to the next using the keypad. The selected measuring point is by default
assigned preferred status and is scanned at half the measuring rate; all other
active channels are also scanned but in the background (semi-continuous
mode). The data is output on the display and, if available, to an analog output.
To shorten the response time when there are many measuring points the meas-
uring rate can be set to continuous and increased accordingly.
Measured values
The measured values can be indicated on the display using a variety of menus,
some user-configurable, in 2 font sizes, or in the form of a bar chart. Measured
values are acquired automatically with auto-zero and self-calibration; however,
they can also be corrected and scaled arbitrarily as required. With most sensors
a sensor breakage is detected automatically.
Analog output and scaling
Each measuring point can be scaled by means of analog start and analog end
in such a way that the measuring range thus defined covers the full range of the
bar chart or of an analog output (2 V, 10 V, or 20 mA). At the analog output the
device can output the measured value from any measuring point or a pro-
grammed value.
Measuring functions
With some sensors, to achieve optimal measured value acquisition, certain spe-
cial measuring functions are required. Cold junction compensation is provided
for thermocouples; temperature compensation is provided for dynamic pres-
sure, pH, and conductivity probes; and atmospheric pressure compensation is
provided for humidity sensors, dynamic pressure sensors, and O sensors. On
2
infrared sensors the gain correction parameter is used as emissivity factor.
Measured value smoothing
Measured values of an unstable or strongly fluctuating nature can be smoothed
by means of a sliding average over a number of values programmable from 2 to
99.
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