Scales; Using Chart Scales - Siemens SIREC D Handbuch

4.5.3 Scales.

Scales are used to display and
record all or part of the preselected Output Scale.
The user can effectively zoom all or part of the
available range. The user can also configure the
grids printed on the display. Two sets of 8 scales A
through H can be programmed. Only one of the two
sets is active at any given time. The active set can
be selected via remote switches or from the front
panel using the FUNCtion programming option.
A. Using Chart Scales -
A through H can be programmed. Only one of the
two sets is active at any given time.
•
Each bargraph and/or pen is driven by a point.
Any point in the system can be assigned to
one or more of the pens and/or bargraphs.
•
A scale from A through H is selected for each
point during point programming. Since more
than one point can be assigned to each scale,
programming of the scale parameters is done
separately in the Scales menu.
•
The point assignment connects bargraphs,
pens and chart grids with the corresponding
scale.
To better understand the use of input and output
scaling, and how scaling base points affects the
data, consider the following example and Figure 4-
8.
1. Assume the user wants to record the output
from a pressured transducer which gives a 0 to 5
volt DC output signal. This coincides to a pressure
of 0 to 3000 pounds per square inch (PSI). The
process being monitored typically runs at 2200
PSI ±10%, this is the area of interest. The output
Siemens AG C79000-G7374-C211-01
SIREC D Manual
Two sets of 8 scales
Figure 4-8 Scaling Flow Example
of the transducer which peaks at 5 volts is con-
nected to live input channel 1 and the 10 volt full-
scale range is selected to cover this range. Since
the maximum input voltage will be only 5 volts on
a 10 volt range, use the input scale option to set
the low end at 0.0, and the high end at 5.000
volts. To convert this directly to PSI, the output
scale is set at low point 0.0 and high point 3000.0.
The base point now becomes 0 to 3000 for an in-
put of 0 to 5 volts, scaled linearly across the
range. The engineering units can be set to PSI
and the point tag can be set to any label that iden-
tifies the process. All of this is accomplished in the
Points menu. Apply scale A to the base point, this
too is selected in the Points menu.
2. It is then necessary to define chart scale A to
suit the requirement. In order to maximize the dis-
play resolution, the user is interested in pressure
ranges from 2000 to 2500 only. Scale A is thus
set for a low end of 2000, a mid-range of 2250
and a high end of 2500. This scale point is now
assigned to the bargraph and the chart graph. The
chart will display from 2000 to 2500 as will the
bars, maximizing the display resolution for the
value of interest.
3. You can choose to record this particular value,
in other words, what you see on the chart is what
is recorded to disk, values from 2000 to 2500. Or,
if desired, you can choose to record a second
point which will show pressures from 0 to 3000.
To do this, use channel 1 as a base point for a
computational channel and program an equation
with the basepoint as the only term, which is then
recorded to disk.
Programming
4-15