Emerson Process Management GmbH & Co. OHG
3-22
X-STREAM XE
Short Form Manual
HASXEE-SFM-HS
05/2017
3.8 Checking the Settings
Tab. 3-2:
Analog Output Signals Settings and Operational Modes
Operation Modes acc. NAMUR NE 43
Output signal, if
"OutRange" "FailMode"
Failure sig-
nal level acc.
NE 43
Measured
value is
valid
Measured value is
below lower limit
("Low scale")
Measured value is
above upper limit
("High scale")
An internal
failure oc-
cured
Cable is
severed
0-20 mA
Track
-
0…20 mA
< -19 mA
> 21.7 mA
undefined
0 mA
4-20 mA
Track
-
4…20 mA
< -19 mA
> 21.7 mA
undefined
0 mA
0-20 mA
LOW - 10 %
below
0…20 mA
-0.20 mA*
(-1.80…-0.01 mA)**
20.50 mA*
(20.01…21.50 mA)**
-2 mA
0 mA
4-20 mA
LOW - 10 %
below
4…20 mA
3.80 mA*
(2.20…3.99 mA)**
20.50 mA*
(20.01…21.50 mA)**
2 mA
0 mA
0-20 mA
HIGH + 10 %
above
0…20 mA
-0.20 mA*
(-1.80…-0.01 mA)**
20.50 mA*
(20.01…21.50 mA)**
> 21.7 mA
0 mA
4-20 mA
HIGH + 10 %
above
4…20 mA
3.80 mA*
(2.20…3.99 mA)**
20.50 mA*
(20.01…21.50 mA)**
> 21.7 mA
0 mA
Note!
The application of values marked * or ** depends on the setting of "Cut Mode" (for more information
Chapter 6 of the X-STREAM
Enhanced Series
instruction manual).
If "
OutRange
" is set to
0-20 mA
, a 20 mA signal
is generated, if the measured concentration
equals "
Max Scale
". A 0 mA signal is generated
if the sample gas concentration 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 failure and
accepts a gas concentration of 0.
The commonly used method of detecting a
severed cable is to apply an offset: a concentra
-
tion corresponding to the lower range value is
assigned an analog signal of 4 mA, enabling to
detect a severed or disconnected cable.
This live zero mode is activated by setting “
Out
Rang
e” to
4-20 mA
.
Operation Modes Conforming to NAMUR 43
(NE 43) Recommendations
The operation modes described above do not
generate a signal which enables detection of
a failure in the measurement system. In such
cases the behaviour of the output signal is
undefined: either the last value is held, or a
random value is sent. System failures thus can-
not be detected by an external data acquisition
system.
NE 43 gives recommendations for setting ana-
log outputs in order to avoid these situations.
They are implemented by X-STREAM analyzers
as follows:
Setting "
FailMode
" to
HIGH +10%
or
LOW -10%
defines specific analog output signals for fail
-
ures. Since these values are not output under
normal operation conditions, a data acquisition
system is enabled to distinguish between the
following situations (table 6-1):
• Valid signal (signal within valid range; col-
umn
C
)
• Signal out of range (signal rises or falls
slowly to the limits given in columns
D
or
E
and holds this value until the concentration
returns to a valid level).
• Failure (signal out of range; column
F
)
•
Severed cable (no signal; column
G
)
