Using Bipolar Ranges (Magnitude Plus Sign) - Automation Direct DL405 User Manual

9–16
F4–08RTD 8-Channel RTD Input
Using Bipolar
Ranges
(Magnitude Plus
Sign)
4 4 4
430 440 450
With bipolar ranges, you need some additional logic because you need to know if the
value being returned represents a positive voltage or a negative voltage. For
example, you may need to know if the temperature is positive or negative.
The following program shows how you can accomplish this. Since you always want
to know when a value is negative, these rungs should be placed before any
operations that use the data, such as math instructions, scaling operations, and so
forth. Also, if you are using stage programming instructions, these rungs should be
in a stage that is always active. Although this example shows all eight channels, you
only need the additional logic for those channels that are using bipolar input signals.
SP1
Store Channel 1
X30 X20 X21 X22
Store Channel 2
X31 X20 X21 X22
Store Channel 3
X32 X20 X21 X22
Program is continued on the next page.
Loads the complete data word into the
LD
accumulator. The V-memory location
V40400
depends on the I/O configuration. This
example assumes the module is in the
X0–X37 slot. See the CPU memory map.
This instruction masks off the channel data
ANDD
and excludes the sign bit. Without this, the
K7FFF
values used will not be correct, so do not
forget to include it.
It is usually easier to perform math
BCD
operations in BCD, so it is best to convert
the data to BCD immediately. You can leave
out this instruction if your application does
not require it. Do not use with internal PID
loops because the PV requires binary data.
This rung looks at fault bit X30 (the broken
OUTD
transmitter bit for channel 1) ANDed with
V3000
active channel bits X20–X22. When the
active channel bits are true and there is no
C100 transmitter fault, channel 1 data is stored in
V3000.
RST
X17
C100 If the sign bit X17 is on, then control relay
C100 is set. C100 can be used to indicate a
SET
negative channel 1 value or to call for a
different message on an operator interface.
This rung looks at fault bit X31 (the broken
OUTD
transmitter bit for channel 2) ANDed with
V3002
active channel bits X20–X22. When the
active channel bits are true and there is no
C101
transmitter fault, channel 2 data is stored in
RST
V3002.
X17
C101
If the sign bit X17 is on, then control relay
SET
C101 is set. C101 can be used to indicate a
negative channel 2 value or to call for a
different message on an operator interface.
This rung looks at fault bit X32 (the broken
OUTD
transmitter bit for channel 3) ANDed with
V3004
active channel bits X20–X22. When the
active channel bits are true and there is no
C102
transmitter fault, channel 3 data is stored in
RST
V3004.
X17
C102
If the sign bit X17 is on, then control relay
SET
C102 is set. C102 can be used to indicate a
negative channel 3 value or to call for a
different message on an operator interface.