The Interface Solution Experts
19
HIM
Smart HART
Loop
Interface and Monitor
Full
Primary
Variable
range
(in PSI)
Control
level
range
(50% to 100%
of total level)
Digital
Pressure
Transmitter
HART Monitor
(120 PSI)
HART
Signal
Loop Display
(reads 0-100%
of control
level)
Controller maintaining
control from 50-100% of full scale
(60-120 inH 0/2.15-4.3 PSI).
4-20mA from HART Monitor
should represent 60-120
inH 0.
4-20mA
Signal
4-20mA
Signal
2
2
Figure 15.
Scaling Tab
Figure 16.
The HIM’s Scaling feature works to get the most out of your existing process instruments
Scaling Parameters
The
Scaling tab allows you to configure the values for
scaled variables. To scale the selected variable, enter
the values into the appropriate boxes, then click on the
Transfer menu and click Download to transfer the new
scaled values to the HIM. (If any scaled variable was
selected in the
Display, Alarm or Analog Outputs tabs,
then the corresponding scaled variable section will
become active for editing).
The HIM’s versatile scaling feature has many possible
applications, as is shown in the illustration below.
Suppose you are using a digital pressure (DP)
transmitter to measure the level of a tank in either
centimeters/inches or PSI. Since the tank is only 300
centimeters (10 feet) high, the full range of the primary
variable (PV) output from the DP transmitter is 0-4.3
PSI. You want to display the full level range (in
centimeters/inches of water) on the HIM. You also
need to control the level from 50% to 100%, since the
tank must be at least 50% full at all times. Finally,
your existing loop indicator and level controller needs
4-20mA to represent 150 to 300 centimeters (60 to 120
inches) of water. How do you do this?
Scaling Illustration
1. Since you want to display the full level range in
inches of water (in H
2
O) on the HIM, and the HIM is
reading PSI as the primary variable, first go to the
Display tab and select Scaled PV as your display
source.
2. Go to the
Scaling tab and set up the PV Zero and
PV Full values, and the Scaled PV Zero and Full
values.
PV Zero would be 0 (PSI) and PV Full would
be 4.3 (PSI).
Scaled PV would correlate to zero being
0 in H
2
O and full being 120 in H
2
O. The HIM should
now (after downloading) display the full range in
in H
2
O.
3. To manipulate the HIM’s analog output, go to the
Analog Outputs tab. Select Scaled PV as the Output 1
source. Since you need to control the level from 50%
to 100%, the
Input Range should be 60 to 120 in H
2
O
and the
Output Range should be 4mA to 20mA.
