HIM
16
The Interface Solution Experts
Smart HART
Loop
Interface and Monitor
It then takes the HART master five seconds to repeat
the poll to the one device being monitored by the HIM.
the HIM
Timeout Period
must be set at a value greater
than five seconds. In this example, we will use seven
seconds. The HIM then sees its slave device speak
and waits seven seconds for it to speak again. As long
as the HIM sees a new message from its slave device
its outputs are updated based upon the measured
variables. If the slave device does not speak within the
seven second period, the HIM declares a “No HART”
situation and sends its outputs to the failed communi-
cations values.
To use this feature, proceed with the following steps:
1. Select the
Listen (Specified Slave)
button.
2. Enter your desired value into the
Timeout Period(s)
text box.
Factory default is 5 seconds. The maximum Timeout
Period is 30 seconds.
3. Set the exact slave address of the instrument you
wish to monitor. Click the
Set Slave Address
button.
This brings up the
HART Slave Device Long Format
Address Settings
screen (Figure 8). Enter the required
information into the appropriate text boxes.
The
Manufacturer’s ID
and
Device Type ID
for the
instrument that the HIM will listen to are available from
the HART Foundation website at
www.hartcomm.org
and/or the instrument manufacturer.
Values obtained from the HART website are in HEX
code. The HIM does not use HEX code; you must
convert this value to Decimal code.
Figure 9.
HART Slave Device Long Format Address Settings
Screen
To convert HEX to Decimal code, perform the
following steps:
Access the Calculator feature in Microsoft
Windows® by opening the
Start
menu. Next,
select
Programs
then
Accessories
and finally
Calculator
.
Ensure that the Calculator is in
Scientific
mode.
To do this, select the
View
dropdown menu
and choose
Scientific
.
Click the
Hex
radio button and enter the HEX
code
value.
Next, click the
Dec
button and the value will be
converted into the Decimal value.
Enter the converted value into the proper param
eter.
The
Device ID Number
is the serial number of
the exact device to which the HIM will listen.
4. Once complete, press
OK
.
Download the information to your instrument once you
are finished.
Auto Clear Status Bit
Most HART instruments indicate when a device’s
configuration has been changed. This indication
(status bit) can be reset by sending HART command
38–reset configuration changed. Checking the
Auto Clear Status Bit
box causes the HIM to issue
this command whenever the HART instrument it is
monitoring has its configuration changed. However,
the HIM can also be set to alarm on this bit (see
Programming the Alarm Parameters
). If the HIM is
both set to alarm and to auto clear, then it will do both–
going into alarm mode and resetting that indication.
Quick Read/Set
The
Quick Read
button causes the PC Configuration
Software to read the communications information
from the attached HIM; the
Quick Set
button causes
the software to configure the HIM’s communications
settings to match those of the PC Software.
HART Device Info
This box displays the identification and revision
information of the monitored HART instrument.
