Campbell Hausfeld 4-Channel Current/Voltage SDM-CVO4 - Manual (Page 20)

SDM-CVO4 4-Channel Current/Voltage Output Module
range of -20
°C to +50°C would be scaled so at -20C the output is 0 mV and at
+50
°C the output is 10000 mV. To do this with the SDM-CVO4 you would use
the mathematical functions of the datalogger to calculate a scaled value in a new
input location, so that the value is -5000 when the temperature is -20
°C and
+5000 at +50
°C.
The datalogger limits the output of the SDM-CVO4 so that even if the measured
value exceeds the intended range (i.e. the scaling value exceeds
±5000) the signal output is limited to the equivalent output at -5000 or +5000.
Therefore the datalogger instruction does not normally need to have extra
instructions to limit the scaling value range. However for displays or input devices
which require a current signal of 4-20 mA, the datalogger program needs to
include extra instructions to prevent the scaling value going below
- 3000 (see the examples below) and thereby setting the lowest possible output to
4 mA.
When checking the output of the SDM-CVO4 against the scaling value you
should be aware that the output changes in discrete steps, e.g. 2.5 mV in voltage
mode. When the datalogger works out which of these discrete steps to set for a
given scaling value, a combination of floating point mathematics followed by
truncation to an integer value is made. This will sometimes result in the transition
from one output step to the next not happening at the exact midpoint value of each
2.5 mV step, although it should happen within a limit of ±0.5 in terms of the
scaling value stored in the input location.
The number of repetitions, parameter 1, specifies the total number of
SDM-CVO4 output channels to be set. The address of the first SDM-CVO4 is
specified with parameter 2; multiple SDM-CVO4s must have consecutive
addresses. Parameter 3 is the starting input location containing the scaling value
for the first output channel of the first SDM-CVO4. Subsequent scaling values
must be contained in consecutive input locations immediately after the first input
location specified in parameter 3.
For example, two SDM-CVO4s can be used to output eight signals, which are
contained in input locations 15 to 22. There are eight repetitions, and so eight (8)
is entered for parameter 1. The SDM-CVO4s must have consecutive addresses
(e.g. 31 and 32), and so parameter 2 would contain 31 in this case. Fifteen (15)
would be entered for parameter 3.
Table 6-1. Description of Instruction 103
Par. Data
Number Type Description
01: 2 Reps — Number of analogue outputs
02: 2 Address of SDM-CVO4 in base 4 (00 to 33)
03: 4 Input loc. holds scaling value for the output level
Setting the Reps parameter to 0 (Zero) will cause the addressed SDM-CVO4 to
shut down, turning off all its outputs. It will turn on channels 1 and 2 at the next
execution of Instruction P103 where the reps parameter is 1 or 2. If the reps
parameter is greater than 2, then all the channels will be turned on.
Refer to the manual for the datalogger being used for full details of the execution
time of Instruction 103. All of the outputs of the SDM-CVO4 will change
simultaneously approximately 10ms after the instruction is completed by the
datalogger, or 100ms after power-up.
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