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Emerson Process Management GmbH & Co. OHG 6-33
X-STREAM X2
Instruction Manual
HASX2E-IM-HS
02/2012
6
Software Menus
6.2 Menu System - Signal Range
The signal range for the analog outputs is set
via the signal "Range" parameter.
When set to 0-20 mA, a 20
mA signal is ge-
nerated when the measured concentration is
equal to the upper range value
. A 0 mA signal
is generated when the sample gas concentra-
tion is 0 (dead zero).
However, a severed cable also results in a
signal value of 0. An external data acquisition
system thus cannot detect such an error and
simply registers a gas concentration of 0.
The usual method of detecting a severed cable
is to use an offset: a concentration correspon-
ding to the lower range value is assigned an
analog signal of 4 mA, allowing the detection
of a severed or disconnected cable.
This live zero mode is activated by setting the
“SignalRange” parameter to 4-20 mA.
Operation modes conforming to NAMUR 43
(NE 43) recommendations
The operation modes described above do not
generate a signal which would allow detection
of a failure in the measurement system. In
such cases the behaviour of the output signal
is undened: either the last value is held, or
a random value is sent. System failures thus
cannot be detected by am external data acqui-
sition system.
NE 43 contains recommendations for setting
analog outputs in order to avoid these situa-
tions, and are implemented by X-STREAM
analyzers as follows:
6.2.3.4.1.1 Signal Range Menu
Setting range parameters to values other than
0-20 mA or 4-20 mA denes specic analog
output signals in the case of a failure. Since the-
se values do not occur when there is no error,
a data acquisition system is able to distinguish
between the following conditions:
• severed cable (no signal (0 mA)),
• failure (signal outside of valid range as in
table 6-1, but not 0)
• valid signal (signal within valid range as in
table 6-1)
• signal out of range (signal rises or falls slowly
to the limit given in table 6-1 and holds this
value until the concentration returns to a valid
level).
Setup..
In/Outputs..
Analog outputs..
SignalRange: