Mitsubishi Electric R60AD8-G - 1.5 Scaling Function

24
1 FUNCTIONS
1.4 A/D Conversion Method
Primary delay filter
Depending on the set time constant, transient noise of analog input is smoothed. The smoothed digital output values are
stored in the buffer memory area.
Time constant is the time taken for the digital output value to reach 63.2% of the steady-state value.
The following shows the relational expressions of time constants and digital output values.
When n = 1
*1
Y
n
= 0
When n = 2
When n  3
*1 The corresponding bit of 'A/D conversion completed flag' (Un\G42) turns on when n  2.
Ex.
Digital output value when an analog input value is changed from 0 to 1V
The following figure shows the change of the digital output value with the input range of 0 to 10V and time constant
(Conversion cycle  Primary delay filter) of 40ms.
After 40ms from the analog input value becomes 1V, the digital output value reaches 63.2% of the digital output value of when
the sampling processing is selected.
Y
n
: Current digital output value
Y
n
-1: Last digital output value
n: Number of samplings
X
n
: Digital output value before smoothing
X
n
-1: Last digital output value before smoothing
T: Conversion time
TA: Time constant
Y
n
= X
n-1
+
Δt + TA
(X
n
- X
n-1
)
Δt
Y
n
= Y
n-1
+
Δt
Δt + TA
(X
n
- Y
n-1
)
040
0
0.2
0.4
0.6
0.8
1.0
1.2 3840
3200
640
1280
1920
2560
63.2%
Analog input value Digital output value
0
Elapsed time (ms)
Digital output value
Analog input value (V)