Videographic Recorders
SM1000 and SM2000
2 Math Configuration
IM/SM2000ADV
Issue 7
15
2.9.6 Switch Functions – Figs. 2.9 and 2.10
The switch functions, HS (High Select), MS (Median Select) and
LS (Low Select) are used to select between the highest, median
and lowest of three analog values – see Fig. 2.9.
The switch function Mux (Multiplexer) is used to switch between
2 analog values when a third value becomes true – see
Fig. 2.10.
2.9.7 Absolute Value Function – Fig. 2.11
The Absolute Value Function converts any negative value to it's
positive equivalent – see Fig. 2.11.
Therefore, if the Absolute Value Function is used to monitor the
difference between two flows A and B, where Flow A could be
greater than or less than Flow B, the function will always return a
positive value, which represents the unsigned magnitude of the
difference between the flow rates.
2.10 Application Examples
2.10.1 Liquid Flow – Fig. 2.12
Liquid Flow is measured in two ways:
1. Using a linear flow device such as Vortex, Swirl,
Ultrasonic, Turbine and Magnetic Flowmeters
2. Using a differential pressure transmitter across an orifice
plate or wedge.
Corrections can be applied to compensate for variations in
temperature and density – see Fig. 2.12, page 16.
Square Root Extraction and Scaling
Normally, square root extraction and scaling (
) is
achieved in the DP transmitter or using an input linearizer within
the recorder.
If this is not possible, a math block can be used as follows:
Temperature Compensation
Assuming linearization and scaling has been achieved on either
the DP transmitter or linearizer input, temperature compensation
can be calculated as follows:
This is implemented in the recorder (assuming the linearized flow
is on input a1) as follows:
This requires two math blocks:
and
created as follows:
Fig. 2.9 High, Median and Low Select
Fig. 2.10 Multiplexer Operation
Fig. 2.11 Absolute Value Function
°C
80
60
40
20
x
z
y
x
y
z
Output for Hs(x, y, z)
Output for Ms(x, y, z)
Output for Ls(x, y, z)
Output for Mux(x, y, s) when s is true
°C
80
60
40
20
x
s
y
True
False
1
0
F
abs(x)
1
0
-1
t
x
Q
K h
=
Qc
Q
1
t
r
t
b
)
a
–
(
+
---------------------------------
=
Qc
a1
t
r
t
b
a
1
+
×
–
---------------------------------
=
m2
t
r
t
b
a
1
+
×
–
=
m3
a1 m2
⁄
=