Emerson Rosemount X-Stream Series, Instruction Manual

Page: 227 / 536

Emerson Process Management GmbH & Co. OHG
6-65
X-STREAM XE
Instruction Manual
HASXEE-IM-HS
10/2012
6
Software Menus
6.2.3 Setup Menu
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 concen
-
tration 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 ca-
ses the behaviour of the output signal is unde
-
fined: either the last value is held, or a random
value is sent. System failures thus cannot 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 failu
-
res. 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; co-
lumn
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 )
Tab. 6-2: Analog Output Failure Modes
6.2.3.4.1.1.1 Operation Modes Acc. NAMUR NE 43
Output signal, if
Column A B C D E F G
"OutRange" "FailMode"
Failure
signal 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
occured
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"
(
page 6-67)
.