Yokogawa HIMHART - Manual (Page 16)

HIM
16 The Interface Solution Experts
Smart HART  Loop
Interface and Monitor
Analog Outputs Parameters
The HIM comes with either 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 program the Analog Outputs
parameters, change the settings 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.
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.
Figure 12. Analog Outputs Tab
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.