Honeywell MCT404 User Manual page 19

2. Before you begin
2.2. Transmitter/Communication characteristics
As indicated at key number (4) in Figure 2-2, the Honeywell Smart Transmitter includes a path for
digital communications between the sensor (via the microprocessor) and the 4-20 mA current loop that
connects the transmitter to external communications devices such as process control equipment
("receiver") and/or to a MC Toolkit.
Digital to-Analog Conversion and Transfer
The digital-to-analog converter (D/A) shown at key number (5) in Figure 2-1is shown as a box with a
dotted line to indicate that analog output mode is a user-selectable feature, for use in an application
whose receiving equipment requires an analog
Note that the Digital I/O (Comm) (communications) box (4) is shown in Figure 2-1with solid line to
indicate that the digital communications path is available at all times, even when analog mode is selected.
Honeywell Transmitter Output - Analog Mode
The diagram in Figure 2-2 provides an overview of a Honeywell transmitter operating in the analog
mode.
Analog (PV Signal) Output
The vertical scale at the left of Figure 2-2is an example of the available range (LRL to URL) of a
pressure transmitter sensor as built and characterized at the factory. The area of this scale that is
highlighted in white represents the configured process operating range (LRV to URV) - in this case, from
100 in H O to 225 in H
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Note that Engineering Units (EUs) shown in Figure 2-2 are included here only for reference. The
transmitter does not perform any conversion of the base units' value to Engineering Units. All
conversion to EUs is performed in the MC Toolkit and/or in other receiving devices such as operating
panels associated with control equipment. Default conversion is to inches-H
The output of a Honeywell transmitter operating in the analog mode is a scaled value (0% - 100%) of
current (4 mA to 20 mA), whose lower and upper limits correspond to the configured operating range
(LRV-URV), respectively.
At the right of Figure 2-2, "PVEULO", "PV", and "PVEUHI" are examples of parameter names that
appear on Honeywell control equipment, which are used as follows.
Parameter Name
PVEULO
PV
PVEUHI
Revision 3
input.
O.
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Parameter Description
Process Value , Engineering Units, Low
Process Value
Process Value , Engineering Units, Low
MC Toolkit (MCT404) User Manual
O @39F.)
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Display Examples
PVEULO 100 in H20
PV 175 in H20
PVEUHI 225 in H20
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