Emerson Rosemount Analytical X-STREAM Enhanced Series - Tab. 3-2: Analog Output Signals Settings and Operational Modes

Emerson Process Management GmbH & Co. OHG3-22
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 undened 0 mA
4-20 mA Track - 4…20 mA < -19 mA > 21.7 mA undened 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
Range” 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
undened: 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%
denes specic 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)