Writing The Control Program; Update Any Channel; Calculating The Digital Value - Automation Direct DL405 User Manual

Writing the Control Program

Update Any As mentioned earlier, you can update any channel per scan using regular I/O
Channel 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 selection outputs to determine which channel gets updated (more on
this later).
Output Enable
Bit
Calculating the Your program has to calculate the digital
value to send to the analog module.
Digital Value
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.
A + 10U
F4–04DAS–1 4-Channel Isolated 4–20mA Output
V40502
MSB
Bit 15 14 13 12 11 10 9 8 7 6
Y Y Y
5 5 4
7 0 7
Unused Bits
65535
10(H * L)
F4–04DAS–1
8pt 8pt 32pt 16pt
Output Output Output Output
Y0 Y10 Y20 Y60
– – – –
Y7 Y17 Y57 Y77
V40500
V40503
MSB
LSB
Bit 15 14 13 12
5 4 3 2 1 0
Y
Y
4
3
0
7
Channel
Select Bits
A + U 65535
H * L
A = analog value (0 – 65535)
U = engineering units
H = high limit of the engineering
unit range
L = low limit of the engineering
unit range
65535
A + 494
1000 * 0
17–9
16pt 16pt
Input Input
V40501
LSB
11 10 9 8 7 6 5 4 3 2 1
Y Y Y
3 2 2
0 7 0
Data word contains
16 data bits
A + 32374
0