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5-36
Instruction Manual
HASAxE-IM-HS
05/2006
Emerson Process Management GmbH & Co. OHG
5-4 Menu System - Analog Output Setup Menu
Enter this line to select the analog outputs
ranges. In addition this entry allows to setup
the analog outputs to follow the NAMUR NE43
recommendations.
Normally a gas concentration of "0" generates
a similiar analog output of 0 mA.
As a signal cable break results in a "0" signal,
too, an external data acquisition is not capable
of detecting such a failure and accepts a gas
concentration signal of "0".
Such an analog output operation mode is
selected by setting the "Signal range"
parameter to 0-20 mA
The commonly used methode to detect cable
breaks is driving the analog outputs in LIFE-
ZERO mode: a concentration corresponding
to the lower measuring range limit (e.g. "0") is
assigned to an analog signal of 4 mA. Thus a
failure like cable break is clearly detectable by
a signal of 0 mA.
This LIFE-ZERO mode is selected when
setting parameter "Signal range" to
4-20 mA.
Operation Modes corresponding to
NAMUR Recommendation 43 (NE 43)
Both modes described above do not provide
a signal capable to detect a failure within the
measuring system. Here the output signal
behaviour is undefined: either it keeps the last
value or is set to an arbitrary value: Measuring
system failures are not detectable by an exter-
nal data acquisition system.
5-4-3-4-1-2 Analog Output Range Setup
SignalRange: 4-20mA
NE43 gives recommendations how to setup
analog outputs to avoid above situation and the
X-STREAM series analyzers consider NE 43:
Setting "Signal range" to values other than
0-20 mA or 4-20 mA defines specific signal
levels for analog outputs in case of measuring
system failures. During normal operation these
values are not output, so an data acquisition
system is capable to distinguish between
• cable break ("0" signal),
• failure (signal outside accepted range, but
differing from "0")
• valid measuring value(signal within accepted
range)
In case there is no failure but only a measuring
range overrun or underrun the output signal will
increase / decrease until it is equal to the limit
given in table 5-1 below and then keeps this
value until the measuring signal is back within
the measuring range.
Special feature for single channel
instruments!
These special NAMUR compatible operating
modes adjust the channel 2 analog output to a
value below the accepted range but above the
failure limit. This ensures that a data acqusition
system recognizes the signal as a non valid
measuring signal and does not give an alarm
signal due to a missing measuring channel.