Writing The Control Program - Automation Direct DL405 User Manual

13–10
F4–04DA–1 Analog Current Output

Writing the Control Program

Update Any
Channel
Calculating the
Digital Value
As mentioned earlier, you can update any channel each scan using regular I/O
instructions, or any number of channels per scan using immediate I/O instructions.
The following diagram shows the data locations for an example system. You use
the channel select outputs to determine which channel gets updated (more on this
later).
Unused
Your program has to calculate the digital
value to send to the analog module.
There are many ways to do this, but
almost all applications are understood
more easily if you use measurements in
engineering units. This is accomplished
by using the conversion formula shown.
You may have to make adjustments to
the formula depending on the scale you
choose for the engineering units.
Consider the following example which
controls pressure from 0.0 to 99.9 PSI.
By using the formula, you can easily
determine the digital value that should
be sent to the module. The example
shows the conversion required to yield
49.4 PSI. Notice the formula uses a
multiplier of 10. This is because the
decimal portion of 49.4 cannot be
loaded, so you adjust the formula to
compensate for it.
F4-04DA-1
8pt 8pt 16pt
Output Output Output Output
Y0 Y10 Y20 Y40
– – –
Y7 Y17 Y37 Y57
V40500
V40501
MSB
Data Bits
Output Channel
Enable Select Bits
A + U 4095
A = analog value (0 – 4095)
U = engineering units
H = high limit of the engineering
L = low limit of the engineering
A + 10U
A + 494
A + 2023
16pt 16pt 16pt
Input Input
–
V40502
LSB
H * L
unit range
unit range
4095
10(H * L)
4095
1000 * 0