AutomationDirect DL205 - Writing the Control Program; Calculating the Digital Value; The Conversion Program

DL205 Analog Manual, 7th Edition Rev. D
10-11
Chapter 10: F2-08DA-1, 8-Channel Analog Current Output
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Writing the Control Program
Calculating the Digital Value
The control program must calculate the digital
value that is sent to the analog output. Several
methods can be used to do this, but the best
method is to convert the values to engineering
units. This is accomplished by using the
formula shown.
Adjustments may have to be made to the
formula depending on the scale of the engi-
neering units.
Consider the following example which controls pressure from 0.0–99.9 PSI. Using the
formula will calculate the digital value to be sent to the analog output. The example shows
the conversion required to yield 49.4 PSI. The multiplier of 10 is used because the decimal
portion of 49.4 cannot be loaded in the program, so it is shifted right one decimal place to
make a usable value of 494.
The Conversion Program
The example program shows how to write the program to perform the engineering unit
conversion. This example assumes that a BCD value has been stored in V2300 and V2301 for
channels 1 and 2 respectively.
NOTE: The DL205 has many instructions available so that math operations can simply be performed using BCD format.
Do the math in BCD, then convert to binary before writing to the module output.
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For 0–4095 output format
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
TheLDinstruction loads the engineering unitsusedwithchannel 1 into
theaccumulator.This exampleassumesthe numbers areBCD.Since
SP1 is used, this rung automatically executes on every scan. Youcould
alsouse an X, C, etc. permissive contact.
LD
V2300
SP1
MUL
K4095
DIV
K1000
Multiply theaccumulatorby 4095 (tostart theconversion).
Divide theaccumulator by 1000 (becauseweusedamultiplierof 10,
we have to use1000 instead of 100).
OUT
V2000
Storethe BCDresult in V2000 (the actual stepsrequiredtosendthe
data areshownlater).
TheLDinstruction loads the engineering unitsusedwithchannel 2 into
theaccumulator.This exampleassumesthe numbers areBCD.Since
SP1 is used, this rung automatically executes on every scan. Youcould
alsouse an X, C, etc. permissive contact.
LD
V2301
SP1
MUL
K4095
DIV
K1000
Multiply theaccumulator by 4095 (tostart theconversion).
Divide theaccumulator by 1000 (becauseweusedamultiplierof 10,
we have to use 1000 instead of 100).
OUT
V2001
Storethe BCDresult in V2001 (the actual stepsrequiredtosendthe
data areshownlater).
A = 10U
4095
A = 494
4095
A–2023
10 (H–L) 1000–0)