Writing The Control Program - Automation Direct DL405 User Manual

12–12
F4–04DA 4-Channel Analog Output

Writing the Control Program

Update Any
Channel
Calculating the
Digital Value
As mentioned earlier, you can update any channel or any channels during the same
scan. The following diagram shows the data locations for an example system. You
use the channel selection outputs to determine which channel gets updated (more
on this later).
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.
4095
A + 10U
10(H * L)
4095
A + 494
1000 * 0
A + 2023
F4-04DA
8pt 8pt 16pt 16pt
Output Output Output Output
Y0 Y10 Y20 Y40
– – – –
Y7 Y17 Y37 Y57
V40500 V40502
V40501
MSB
Channel Data Bits
Select Bits
A + U 4095
H * L
A = analog value (0 – 4095)
U = engineering units
H = high limit of the engineering
unit range
L = low limit of the engineering
unit range
16pt 16pt
Input Input
LSB