Somat eDAQlite User Manual Download

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Somat eDAQ

lite

136

I2773-4.

Using the Integrator to Measure Accumulated Pulse Counts

The use of the Integrator computed channel to yield accumulated counts varies based on the selected output data type.

•

32-Bit Unsigned: The most efficient way to use the Integrator computed channel is with this data type; the integrator
can then accumulate up to 4294967295 counts. This is the suggested approach for simply counting pulses or events.
The scaling to hertz is performed by an associated scale factor used only when needed, such as for DataMode storage.
Therefore, the output data stream is the stream of unsigned integer counts.

•

32-Bit Float: If the this output mode is used, then the scale factor field in the Integrator should be set to the reciprocal
of the pulse counter sample period to yield counts; additional scaling can be incorporated into the scale factor field for
conversion to distance, revolutions, etc. It should also be kept in mind that a 32-bit float can only accumulate about 16.7
million counts before it saturates as an integral counter. The scaling to hertz is performed on a sample-by-sample basis
as the data is acquired.

For more information on pulse counter inputs, see

“Pulse Counter” on page 111

7.2.5

Pulse Counter

The Pulse Counter computed channel is used to measure pulse frequencies primarily
in conjunction with digital inputs. Each FALSE to TRUE transition signifies the end of
a pulse period and initiates an update of the current pulse frequency, which is output
at a user-defined rate. The pulse counter frequency also updates if the time period
since the last transition exceeds the current pulse counter frequency output, resulting
in improved response as the pulse train slows or stops.

NOTE

The current pulse frequency initializes to 0 Hz and remains at this initial value until two
FALSE to TRUE transitions occur.

The accuracy of the pulse frequency measurements is dependent on the sample rate
of the digital input channel only (i.e., it is not dependent on the output sample rate
which is set indirectly by the factor parameter). For example, using an input channel
sampled at 2000 Hz provides 1% accuracy of a 20 Hz pulse signal or 0.1% accuracy
of a 2 Hz pulse signal. As a rule of thumb, the input sample rate should be 100 times
the maximum expected pulse frequency to provide 1% or better accuracy over the
entire range of pulse frequency content.

Input Channel

The input channel data type must be 8-bit unsigned (logical).

Output Data Type

The output channel data type is 32-bit float.

Output Rate Factor

Specify the desired down sample factor which sets the output sample rate based on
the sample rate of the input channel. For example, if the input channel sample rate is
2000 Hz, a factor of 100 results in an output sample rate of 20 Hz.

Cal Scale Factor

Specify the desired scale factor for converting measured pulse frequency in Hz to the
desired engineering units.

HBM: public