The Interface Solution Experts
21
HIM
Smart HART
Loop
Interface and Monitor
Analog Outputs Tab
The HIM comes with either one (MB1AO), two (2AO)
or three (3AO) analog outputs. The
Analog Outputs
tab allows you to specify which HART variable is to
be monitored as the source of the analog output, the
input range and output range, and how the output will
react when the variable input is out of range. To pro-
gram the Analog Outputs parameters, change the set-
tings in the
Output1/2/3
boxes, then press
Quick Set
.
See the descriptions below of the various sections of
the screen.
Source
Source
defines the variable that the analog output
will monitor. Notice that selecting one of the scaled
outputs will require you to make changes to the
Scaling
tab, and selecting the Custom Curve option
will require you to make changes to the
Custom Curve
tab.
Figure 14.
Analog Outputs Tab
Input/Output Range
The
Input
or
Output Range
defines the range of the
source input and the range of the analog output.
These two sets of fields can be used to scale the
HIM’s output.
For example, you have a vortex flow meter with
an imbedded RTD that measures the process
temperature, and that temperature is assigned to
the HART Secondary Variable. The full range of the
RTD sensor is from –400°F to +1760°F, but your flow
stream will always be between 0° and 400°F. To scale
the analog output, for Output 1, set the
Source
as SV.
Set the
Input Range
to 0° and 400°F, and the
Output
Range
to 4mA to 20mA. Click
Quick Set
to download
the new configuration file to the HIM.
Output Current Box
The
Output Current
Box on the
Analog Outputs
Tab
displays up-to-the-second information on the value, in
mA, of the analog output.
Fail Mode
The
Fail Mode
setting determines how the HIM will
respond when its monitored input fails. If
Fail Mode
is
set to
High
and the measured input goes out of range,
or any detected error occurs in the HART transmitter,
the analog output will output a 23.6mA signal. If Fail
Mode is set to
Low
and the measured input goes out
of range, or any detected error occurs in the HART
transmitter, the analog output will output a signal that
is 90% of the lower range value below 4mA; it will
output 0mA if the lower range is set to 0mA.
If
Fail Mode
is set to
Hold Last
, the HIM will continue to
output the last value it recorded before the input failed.
If
Fail Mode
is set to
Hold Last Then High
or
Hold Last
Then Low
, the HIM will continue to output the last
value recorded for a set amount of time (according to
Hold Last Duration box), then either fail high or fail low,
respectively.
Quick Set Button
The
Quick Set
button causes the software to configure
the instrument’s analog output settings to match those
currently entered in the PC Software.
Trim Button
The
Trim
button brings up the Trim Menu, allowing
you to set the device’s output to match the reading
of the loop. Refer to the
Programming the Trimming
Parameters
section of this manual for more
information.
