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Managing Your Network Using Fluke DAQ
49
Using Equations with Computed Channels
Each computed channel can have an expression of 250 characters but the
maximum number of characters available in all 60 channels is limited to 6,000
characters.
For example, you could use an equation to calculate the rate of flow in gallons per
second. The rate of flow could be calculated as follows. Since TS is in
milliseconds, you need to divide by 1000 to calculate gallons per second. In this
example, during the first pass, C902 will not be defined and the result will be not a
number (#Inf). However, in subsequent passes, C902 will be defined and will
provide the correct result.
C101 = some fake measurement to force the time calculation
C901 = (TOT-C902)/(TS/1000)
C902 = TOT
Note
You need one physical channel configured in the module that you’re
scanning for this to work even though you’re not using the channel in
the expression.
Computed channels and the time value are initialized to zero at the beginning of
scanning. Physical channels that haven’t been measured are still initialized to
positive infinity.
To measure the total energy used by a simple system, a calculation could be
generated using the equation, energy = R x I^2 * time, as follows:
c101 = Ohms
c102 = Current
c959 = c959+c960
c960 = c101*c102**2*ts/1000
Note
This equation assumes that the resistance and current are constant
for the duration of the time interval. It also does not calculate the
energy used in the first increment of time.