Switch Functions; Absolute Value Function; Application Examples; Liquid Flow - ABB SM2000 User Manual Supplement

Videographic Recorders
SM1000 and SM2000
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.
x
y
z
Fig. 2.9 High, Median and Low Select
The switch function Mux (Multiplexer) is used to switch between
2 analog values when a third value becomes true – see
Fig. 2.10.
x
y
s
Fig. 2.10 Multiplexer Operation
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.
Fig. 2.11 Absolute Value Function
IM/SM2000ADV Issue 7
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
y 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
z
plate or wedge.
Corrections can be applied to compensate for variations in
x
temperature and density – see Fig. 2.12, page 16.
Square Root Extraction and Scaling
Normally, square root extraction and scaling (
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:
Qc
=
This is implemented in the recorder (assuming the linearized flow
is on input a1) as follows:
Qc =
This requires two math blocks:
m2
=
Q
-------------------------------- -
( )a
1 + t – t
r b
a1
-------------------------------- -
×
t – t a + 1
r b
×
t t a 1 and m3 a1 m2
– + =
r b
2 Math Configuration
Q = K h ) is
⁄
created as follows:
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